JP6146104B2 - Schottky barrier diode and electronic device using the same - Google Patents

Description

  The present invention relates to a Schottky Barrier Diode (hereinafter referred to as SBD), and more particularly, to an SBD using a III-V group compound semiconductor and an electronic device using the same.

  Among compound semiconductors, so-called III-V compound semiconductors, for example, nitride semiconductors typified by gallium nitride (GaN) have a characteristic that the band gap is wider than conventional silicon (Si) and gallium arsenide (GaAs). Have.

  For this reason, it has an excellent feature of having a large dielectric breakdown electric field compared to conventional Si and GaAs, and therefore, research and development as a high-power electronic device (or apparatus) or a high-frequency electronic device (apparatus) has been actively conducted. It has been broken.

  For example, a transmission device using SBD (hereinafter referred to as GaN-SBD) using GaN as a group III-V nitride semiconductor has been proposed. (See Non-Patent Document 1)

  FIG. 3 of Non-Patent Document 1 shows a structural cross section of GaN-SBD.

In the figure, an n ⁺ -GaN layer and an n ⁻ -GaN layer are formed on a silicon carbide (SiC) substrate, and a metal (Ni / Au) electrode is formed on the n ⁻ -GaN layer in the center of the figure. Has been. Here, n ⁺ and n ⁻ indicate the concentration of the N-type impurity, and n ⁺ indicates that the concentration is relatively higher than n ⁻ .

The metal electrode serves as an anode electrode of SBD. A Schottky barrier is generated at the contact portion with the n ⁻ -GaN layer, and therefore, the junction between the metal of the anode electrode and the n ⁻ −GaN layer is a Schottky junction.

  The anode electrode is sometimes called a Schottky electrode.

On the other hand, metal (Ti / Al / Ti / Au) electrodes are formed on the n ⁺ -GaN layer on both sides of the anode electrode.

  This metal electrode becomes a cathode electrode in the SBD. The junction of the contact portion between the cathode electrode and the GaN layer is an ohmic junction. The cathode electrode may be referred to as an ohmic electrode.

IEICE Technical Report, WPT 2011-09, 2011, “Microwave power transmission using open ring resonator and GaN SBD”

  Here, since a nitride semiconductor represented by GaN has a wider band gap than an arsenide semiconductor represented by Si or GaAs, it has a characteristic that a breakdown electric field is larger.

  In addition, it has excellent material properties such as high saturation electron velocity and high frequency operation of the device.

  On the other hand, since it has characteristics closer to an insulator, the so-called rising voltage in the current-voltage characteristic when a forward voltage (hereinafter referred to as a forward bias) is applied to the diode when an SBD is produced. (Hereinafter, simply referred to as “rising voltage”) tends to be larger.

  When the rising voltage is high, when a forward voltage is applied, the current flowing at a voltage lower than the rising voltage is small, and therefore the power that can be sent to the load is small. For this reason, the magnitude of the rising voltage is a factor that affects the efficiency in converting an alternating current (AC) signal (or a high frequency (RF) signal) into a direct current (DC) signal. If it is high, there is a problem that the efficiency representing the power conversion characteristic during rectification deteriorates.

  The present invention has been made to solve the above-described problems. Even when a III-V group compound semiconductor having a large band gap is used, the rising voltage of SBD is low, and AC (or RF) to DC is used. An object of the present invention is to obtain an SBD having a high conversion efficiency and an electronic device using the SBD as a rectifying element.

The SBD according to the present invention includes a group III-V compound semiconductor layer formed on one main surface of a substrate, a group III-V compound semiconductor layer, and a first group consisting of a group III-V compound semiconductor layer. The first electrode having a Schottky junction formed at the junction and the III-V group compound semiconductor layer is formed on the second junction with the III-V group compound semiconductor layer. A non-ohmic junction having a second energy barrier lower than the Schottky junction of the Schottky junction, and a cathode electrode connected to the III-V compound semiconductor layer And the first electrode and the second electrode constitute the same anode electrode, and the first junction is formed between the second junction and the cathode electrode,
The III-V compound semiconductor layer includes a GaN-based semiconductor layer and an AlGaN-based semiconductor layer formed on the GaN-based semiconductor layer,
(1) The first electrode or the second electrode is formed on the GaN-based semiconductor layer inside the groove of the AlGaN-based semiconductor layer reaching the GaN-based semiconductor layer, or (2) the GaN-based semiconductor layer reaching the substrate Inside the groove, an AlGaN-based semiconductor layer is formed on the inner surface of the groove and on the substrate, and a first electrode is formed on the AlGaN-based semiconductor layer .

  According to the SBD of the present invention, in addition to the first electrode in which the Schottky junction is formed as the electrode constituting the anode electrode, the height of the barrier of the ohmic junction or the junction interface is the Schottky barrier of the Schottky junction. Since the second electrode in which the non-ohmic junction having the lower second barrier is formed is formed, and the first electrode and the second electrode constitute the same anode electrode, the Schottky junction is formed. A current can be flowed between the second electrode and the cathode electrode with a forward bias lower than the rising voltage.

In addition, since the first electrode and the second electrode have the same potential, the presence of the depletion layer caused by the formation of the Schottky junction causes the second electrode and the second electrode to be in reverse bias and zero bias. It is possible to make it difficult for current to flow between the cathode electrode.
Therefore, the current rises with a forward bias voltage lower than that of the conventional SBD, and thus an SBD with improved conversion efficiency can be obtained.

It is a figure which shows the cross-section of SBD in Embodiment 1 of this invention. It is a figure which shows the planar structure which looked at SBD from the upper direction of the board | substrate in Embodiment 1 of this invention. It is a figure which shows the energy ranking of the conduction band at the time of zero bias in Embodiment 1 of this invention. It is a figure which shows the energy ranking of the conduction band at the time of forward bias in Embodiment 1 of this invention. It is a figure which shows the energy ranking of the conduction band at the time of reverse bias in Embodiment 1 of this invention. It is a figure which shows the cross-sectional structure of SBD of a prior art used for the comparison with Embodiment 1 of this invention. It is a figure which shows the result of having calculated the bias voltage dependence of the current characteristic in Embodiment 1 of this invention and SBD of a prior art. It is a figure which shows the result of having calculated the current density distribution at the time of forward bias in the cross section of SBD in Embodiment 1 of this invention. It is a figure which shows the result of having calculated the current density distribution at the time of forward bias in the cross section of SBD of the prior art used for the comparison with Embodiment 1 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 2 of this invention. It is a figure which shows the energy ranking of the conduction band at the time of zero bias in Embodiment 2 of this invention. It is a figure which shows the energy ranking of the conduction band at the time of forward bias in Embodiment 2 of this invention. It is a figure which shows the energy ranking of the conduction band at the time of reverse bias in Embodiment 2 of this invention. It is a figure which shows the cross-sectional structure used for calculation of SBD in Embodiment 2 of this invention. It is a figure which shows the cross-sectional structure used for calculation of SBD of SBD of the prior art used for the comparison with Embodiment 2 of this invention. It is a figure which shows the result of having calculated the bias voltage dependence in Embodiment 2 of this invention and SBD of a prior art. It is a figure which shows the result of having calculated the current density distribution at the time of forward bias in the cross section of SBD in Embodiment 2 of this invention. It is a figure which shows the result of having calculated the current density distribution at the time of a forward bias in the cross section of SBD of the prior art used for the comparison with Embodiment 2 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 3 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 4 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 4 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 5 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 6 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 7 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 8 of this invention. It is a figure which shows the cross-section of SBD in Embodiment 9 of this invention.

  Each embodiment of the present invention will be described below.

  In the drawings of the embodiments, the same or similar components are denoted by the same or similar numerals, and the description thereof may be partially omitted in the description of the embodiments.

  In the following embodiments, a case where a GaN-based semiconductor, which is a typical nitride semiconductor, is used as an example of a III-V group semiconductor serving as an SBD material will be described.

  Further, the drawings shown in the respective embodiments are diagrams in which a detailed structure or the like is omitted for easy understanding. In addition, the dimension of each part of the structure shown to the figure may differ from an actual thing, and is not limited to the dimension and dimension ratio of a figure.

In an actual SBD, in addition to the SBD structure itself shown in the figure, an element isolation region, various wirings, and the like may be formed. However, it is directly related to the problems, objects, and effects of the present invention. Therefore, the description is omitted in the following description.
Embodiment 1 FIG.

  The first embodiment of the present invention will be described below.

  FIG. 1 is a diagram showing a cross-sectional structure of an SBD in Embodiment 1 of the present invention.

  FIG. 2 is a diagram showing an example of the planar structure of the SBD in the first embodiment of the present invention.

  The cross-sectional structure in FIG. 1 corresponds to the cross section taken along the alternate long and short dash line indicated by B-B ′ in FIG. 2.

  1 and 2, 1 is a substrate, 2 is a GaN layer, 3 is an AlGaN layer, 4 is a cathode electrode, 5 is an electrode A (first electrode), 6 is a protective film, and 7 is an electrode B (second electrode). ), 8 is an anode electrode, 9 is a parasitic resistance A of the diode, 10 is a parasitic resistance B of the diode, and 11 is an active region. Here, the parasitic resistance A is the parasitic resistance of the diode formed by the semiconductor layer between the cathode electrode 4 and the electrode A, and the parasitic resistance B is a plurality of electrodes constituting the anode electrode 8, which are electrodes in this embodiment. The parasitic resistance of the diode by the semiconductor layer between A5 and the electrode B7 is shown.

  In FIG. 1, a GaN layer 2 is formed on one main surface of a substrate 1 as a first semiconductor layer in a group III-V semiconductor layer.

  For example, sapphire, silicon carbide (SiC), or GaN is often used as the material of the substrate 1, but the substrate 1 is not limited to this embodiment as long as the GaN layer 2 can be formed on the substrate 1.

  The substrate 1 may be semi-insulating, N-type, or P-type. In general, the substrate 1 is a semi-insulating SiC substrate having good thermal conductivity and relatively good lattice matching with the GaN layer 2 and less likely to become a parasitic component even in a high frequency region, or inexpensive as a semiconductor substrate. A Si substrate is often used.

  In order to alleviate the generation of lattice mismatch and / or lattice distortion between the substrate 1 and the GaN layer 2 between the material of the substrate 1 and the material of the first semiconductor layer, a so-called buffer layer (buffer layer or relaxation layer) is formed. May also be referred to as a layer).

  The GaN layer 2 may be an intrinsic semiconductor or may be doped with impurities. However, in the present embodiment and each of the embodiments described later, it is assumed that the GaN layer 2 is N-type GaN for easy understanding. .

  The GaN layer 2 may be formed by changing the film thickness, impurity concentration, etc. according to the SBD operating frequency, operating voltage, or the like. Further, the distribution of the impurity concentration may be uniform or may be distributed. For example, the distribution can be controlled by controlling the concentration of impurities added when forming by epitaxial growth.

  On the GaN layer 2, an AlGaN layer 3 is formed as a second semiconductor layer in the III-V group semiconductor layer.

  The junction between the AlGaN layer 3 and the GaN layer 2 forms a heterojunction, and can generate electrons (so-called two-dimensional electron gas) near the junction interface in a state where the SBD is not operated and at zero bias.

  An anode electrode 8 made of a conductive material such as a metal is formed at the upper center of FIG.

  Since the anode electrode 8 is directly electrically connected to the electrode A5 (first electrode) and the electrode B7 (second electrode), the electrode A5 (first electrode) and the electrode B7 (second electrode) Constitutes the same anode electrode in a broad sense. Therefore, the electrode A5 (first electrode) and the electrode B7 (second electrode) have the same potential during the SBD operation.

  In the figure, the electrode A5 and the electrode B7 are in contact with the same semiconductor layer (AlGaN layer 3).

  The junction between the electrode A5 and the AlGaN layer 3 forms a Schottky junction.

  In order to form a Schottky junction at the junction between the electrode A5 and the AlGaN layer 3, for example, the work function of the electrode material of the electrode A5 at the junction is greater than the electron affinity of the III-V group semiconductor layer of the electrode A5. In this way, the SBD is formed by setting conditions such as material, film thickness, and impurity concentration.

  When SBD is present alone or in a zero bias state, a depletion layer (not shown) region is present under the electrode A5 as the Schottky junction is formed, and electrons are depleted there.

  In order to generate a depletion layer in the entire film thickness of the AlGaN layer 3 under the electrode A5, for example, the film thickness of the AlGaN layer 3 under the electrode A5 is formed thin. Although depending on the Al composition of the AlGaN layer 3, for example, a depletion layer can be formed by setting the film thickness to 10 nm or less.

  At this time, the depletion layer reaches the GaN layer 2 and the two-dimensional electron gas at the heterojunction interface is also depleted below the electrode A5, and a discontinuous region of the electron gas is generated.

  The electrode B7 forms an ohmic junction with the AlGaN layer 3. Further, the joint portion of the electrode A5 is formed between the electrode B7 and the cathode electrode 4.

  Note that the electrode materials of the electrode A5 and the electrode B7 may be the same or different, and a Schottky junction and an ohmic junction are generated at the junction due to the formation conditions of the AlGaN layer 3 at the junction of each electrode. That's fine.

  In order to form an ohmic junction at the junction between the electrode B7 and the AlGaN layer 3, for example, the work function of the electrode material of the electrode B7 at the junction is made smaller than the electron affinity of the III-V group semiconductor layer at the junction. In addition, the SBD is formed by setting conditions such as material, film thickness, and impurity concentration. Alternatively, for example, a high-concentration impurity region that causes a tunnel phenomenon is formed in the III-V group semiconductor layer immediately below the junction.

  On the other hand, cathode electrodes 4 made of a conductive material such as metal are formed on both sides of the anode electrode 8.

  The cathode electrode 4 forms an ohmic junction with the AlGaN layer 3.

  The material of the cathode electrode 4 may be any material that can form an ohmic junction at the contact portion with the AlGaN layer 3.

  Further, the electrode A5, the electrode B7, the anode electrode 8, and the cathode electrode 4 do not have to have a single composition or a single film structure, but may have other compositions or structures such as a multilayer film.

  In the figure, an insulating film is formed as a protective film 6 in a region on the AlGaN layer 3 other than the electrode A5, the electrode B7, and the cathode electrode 4. For the insulating film, various insulating materials such as SiN, SiO, and SiON can be used.

  Although the figure shows a case where the AlGaN layer 3 is flat, it is sufficient that the electrode A5 and the electrode B7 are in contact at different joints, and a depletion layer extends in the semiconductor layer under the electrode A5. The shape is not limited.

  Further, a plurality of the structures shown in FIG.

  FIG. 2 shows a so-called comb electrode structure or multi-finger structure in which the structure of FIG.

  In FIG. 2, anode electrodes 8 and cathode electrodes 4 are alternately arranged on the active region 11 of the SBD. In FIG. 2, the electrode A5 and the electrode B7 are not shown because they are hidden under the anode electrode 8.

  Next, the operation principle when the bias voltage applied to the SBD is changed will be described.

  3, 4, and 5 are diagrams (so-called band diagrams) showing the energy levels of the conduction band at the time of zero bias, forward bias, and reverse bias in the first embodiment of the present invention.

  For easy understanding of the principle of the present invention, detailed band structures such as a band structure such as a GaN / AlGaN heterojunction and a relationship between a conduction band and a Fermi level are omitted in the figure, and mainly an electrode and a conductive layer. It shows the relationship of the bottom level.

  In each figure, the energy at the bottom of the conductor in the path along AA ′ indicated by the alternate long and short dash line in FIG. 1, that is, the path from the cathode electrode 4 through the semiconductor layer below the electrode A5 to the electrode B7. The level is shown.

  In each figure, the thin solid line at the center is the energy level at the bottom of the conductor, 12, 15 and 18 are anode voltages (for example, 0 V in 12 of FIG. 3), and 13 is the potential of the cathode electrode 4 (that is, the Fermi of the electrode). Energy barrier A for electron movement when the semiconductor layer 2/3 is viewed from the level), and energy barrier B for electron movement when the semiconductor layer 2/3 is viewed from the potential of the anode electrode 8 (Fermi level) 14 , 16 are electrons, and 17 is an arrow indicating the flow of electrons.

  In each figure, the cathode potential is grounded and shown as a reference (= 0 V), so that anode electrode potential = anode voltage = bias voltage.

  In the case of the zero bias shown in FIG. 3, a depletion layer generated along with the formation of the Schottky junction exists below the junction of the electrode A5, so that the bottom level of the conduction band of the semiconductor layer is the cathode electrode 4. And located above the energy level of the anode electrode B7.

  Therefore, a barrier A13 is generated against the movement of electrons from the cathode electrode 4 to the semiconductor layer, and a barrier B14 is generated against the movement of electrons from the electrode B7 to the semiconductor layer. Therefore, although the cathode electrode 4 and the electrode B7 are both ohmic junction electrodes, it is difficult for electrons to move from the cathode electrode 4 to the electrode B7. Further, since there is a Schottky junction barrier from the cathode electrode 4 to the electrode A5, it is similarly difficult for electrons to move.

  Therefore, at the time of zero bias, the current of the SBD as a whole is difficult to flow.

  Next, as shown in FIG. 4, when a positive anode voltage 15 is applied to the anode electrode 8 as a forward bias, the level of the electrode B7 moves downward. Accordingly, the height of the barrier on the cathode electrode 4 side is reduced, and the electrons 16 can move from the cathode electrode 4 along the electron flow 17 to the electrode B7. Accordingly, an SBD current flows during forward bias.

  In this case, when the anode voltage (positive) 15 is equal to or lower than the rising voltage of the Schottky junction, the electrons 16 cannot move from the cathode electrode 4 to the electrode A, but can move to the electrode B7. Current flows through the SBD even if it is below the rising voltage of.

  When the anode voltage (positive) 15 is equal to or higher than the rising voltage of the Schottky junction, the electrons 16 can flow from the cathode electrode 4 to the electrode B7 and also to the electrode A5. Accordingly, since the electrons 16 flow through both the electrodes A5 and B7, it is possible to pass a larger current than the SBD having the conventional structure.

  As a result, the SBD characteristic has a lower start-up voltage than the SBD having the conventional structure.

  Next, as shown in FIG. 5, when a reverse bias, that is, a negative anode voltage 18 is applied to the anode electrode 8, the level of the electrode B7 moves upward.

  Here, the electrode B7 and the electrode A5 are at the same potential by the anode electrode 8, and the movement path of electrons in the semiconductor layer from the electrode B7 and the electrode A5 to the cathode electrode 4 merges below the electrode A5. Therefore, since the potential is the same, the size of the barrier B 14 does not depend on the anode voltage (negative) 18. For this reason, it is difficult for the electrons 16 to move from the electrode B7 to the cathode electrode 4 side over the barrier B14, so that current does not flow easily.

  In addition, since a reverse bias is applied to the Schottky junction in the electrode A5, a current hardly flows from the electrode A to the cathode electrode 4.

  Therefore, at the time of reverse bias, the current becomes very difficult to flow as a whole SBD.

  As described above, even when the electrode B7 that forms an ohmic junction exists in the anode electrode 8, the rising voltage is maintained while maintaining the voltage-current characteristic that is asymmetric with respect to the bias voltage, that is, the diode characteristic, as the whole SBD. Can be lowered.

  Furthermore, in the heterojunction formation region that is not included in the depletion layer region, the two-dimensional electron gas of the heterojunction reduces the parasitic resistance of the SBD, and therefore the current at the time of forward bias can be further increased.

  FIG. 6 is a diagram showing a cross-sectional structure of a conventional SBD used for comparison with the first embodiment of the present invention in the calculation shown in FIG. 7 described later.

  FIG. 7 is a diagram showing the result of calculating the bias voltage dependence of the current characteristics in the first embodiment of the present invention and the SBD of the prior art. In the figure, the horizontal axis indicates the SBD bias voltage, and the vertical axis indicates the SBD current.

The calculation conditions are as follows: substrate 1 is a semi-insulating SiC substrate having a thickness of 100 μm, GaN layer 2 is 1.2 μm in thickness, N-type impurity concentration is 1E15 cm ⁻³ , AlGaN layer 3 is 20 nm in thickness, and Al composition is 0.23 N The type impurity concentration is 1E15 cm ⁻³ , the length of the junction of electrode A5 is 1 μm, the length of the junction of electrode B7 is 5 μm, and the length of the junction of cathode electrode 4 is 5 μm.

  In the calculation, in order to extend the depletion layer region under the electrode A5 to the GaN layer 2, the calculation is performed for the case where a groove (recess) structure is formed in which only the AlGaN layer under the electrode A5 is 5 nm. That is, a groove having an opening is formed above the AlGaN layer 3, and a part of the electrode is formed inside the groove. Such a groove may be automatically formed depending on the etching ratio between the protective film 6 material and the AlGaN layer 3 material, for example, during an etching process for forming an opening in the protective film 6 for electrode formation, You may make it form the groove | channel of the depth.

  On the other hand, the conventional SBD has basically the same structure as that of the present invention (see FIG. 1) except that an electrode having a Schottky junction having a length of 1 μm is used as an anode electrode.

  However, although the interval between the cathode electrodes 4 in FIG. 6 is the same as that in FIG. 1, the interval between the cathode electrode 4 and the electrode A5 is the same in order to make the parasitic resistance A19 the same condition.

  As can be seen from FIG. 7, in the SBD having the conventional structure, almost no current flows up to the rising voltage of the Schottky junction (about 1 V in the figure) in the forward bias.

  On the other hand, in the SBD of the present invention, it can be seen that the current flows from the region where the forward bias voltage is low, and the rising voltage can be reduced compared to the conventional structure. Further, it can be seen that a larger current is obtained than in the conventional structure even in a region where the rising voltage is exceeded.

  In addition, at the time of reverse bias, it can be seen that almost no current flows in the SBD of the present invention as in the conventional case.

  FIG. 8 is a diagram showing the result of calculating the current density distribution at the time of forward bias (1 V) in the cross section of the SBD (FIG. 1) in the first embodiment of the present invention.

  FIG. 9 is a diagram illustrating a result of calculating a current density distribution at the time of forward bias (1 V) in a cross section (FIG. 6) of the conventional SBD used for comparison.

  8 and 9, only the vicinity of the electrode A5 in which the Schottky junction is formed is shown.

The right side of each figure shows the color coding for each current density and the magnitude of the current density, and the current density increases as the color becomes lighter. The value of current density represents an index in power of 10, for example, current density corresponding to 7.81 in the figure is 10 ^7.81 A / cm ^2.

  From FIG. 8, in the SBD of the present invention, there are many gray regions below the electrode A5, that is, regions with low current density, and white regions, ie regions with high current density, are heterojunctions between the AlGaN layer 3 and the GaN layer 2. It can be seen that it exists near the interface. This indicates that the SBD current does not flow through the electrode A5 but flows from the electrode B7 toward the cathode electrode 4 along the two-dimensional electron gas formation region of the heterojunction interface.

  On the other hand, in the SBD having the conventional structure, a white region having a large current density exists both below the electrode A (broadly defined anode electrode) 5 and in the vicinity of the heterojunction interface. This indicates that a Schottky junction current flows from the anode electrode 8 to the heterojunction interface and then to the cathode electrode 4.

  As described above, it can be seen that the SBD according to the embodiment of the present invention exhibits a characteristic that the current hardly flows at the reverse voltage as in the conventional SBD, and rises from about 0 V in the forward bias.

The effect of the present invention is not limited to the above-calculated conditions. For example, the film thickness of the GaN layer 3 is 0.01 to 10 μm, the N-type impurity concentration is about 1E19 cm ⁻³ or less, and the film thickness of the AlGaN layer 3. 1 to 50 nm, the thickness under the electrode A5 is 0 to 20 nm, the N-type impurity concentration is about 1E19 cm ⁻³ or less, the Al composition is 0.1 to 1, the length of the electrode A5 is 0.1 to 10 μm, and the electrode B7 The length of is considered to be obtained if it is about 0.1 to 10 μm. However, an optimal combination is conceivable for the value of each item.

  In the embodiment of the present invention, a region where the two-dimensional electron gas exists is formed in a region where the depletion layer does not spread, such as between the cathode electrode 4 and the electrode A5.

  When a forward bias voltage is applied to the SBD, the electrons 16 reach the bottom of the anode electrode 4 from the cathode electrode 3 through the two-dimensional electron gas region, and flow out of the SBD from the anode electrode (Schottky electrode) 4. Since the parasitic resistance of the SBD is reduced by the low two-dimensional electron gas, the current increases at the same voltage, and the rising voltage can be further reduced.

Embodiment 2. FIG.
The second embodiment of the present invention will be described below.

  FIG. 10 is a diagram showing a cross-sectional structure of the SBD in the second embodiment of the present invention.

  How to read the figure, components other than the electrode C19, film thickness, impurity concentration, etc., and a plan view seen from above the substrate 1 are the same as those in FIG. 2 of the first embodiment.

  In the figure, 19 indicates an electrode C having non-ohmic junction characteristics.

  11, 12, and 13 are diagrams showing energy levels of the conduction band at the time of zero bias, forward bias, and reverse bias in the second embodiment of the present invention.

  As in the first embodiment, details of the band structure such as a GaN / AlGaN junction and the Fermi level are not shown in the figure for easy understanding of the principle of the present invention.

  Each figure shows the energy level at the bottom of the conductor in the path along CC ′ indicated by the alternate long and short dash line in FIG. 10, that is, the path from the cathode electrode 4 through the semiconductor layer below the electrode A5 to the electrode B7. It is a figure showing the rank.

  The difference from the first embodiment is that since the electrode C19 is a non-ohmic electrode, a barrier C20 against electron movement is further present at the junction interface between the electrode C19 and the AlGaN layer 3 at zero bias. That is.

  The height of the barrier C20 is smaller than the third barrier A13 and the barrier D21 at zero bias. Therefore, the height of the barrier C20 is smaller than the Schottky barrier at the junction of the electrode A5.

  The barrier C20 is formed, for example, such that the electron affinity of the AlGaN layer 3 at the junction is lower than the work function of the electrode C19.

  In the case of the zero bias shown in FIG. 11, the depletion layer region generated with the formation of the Schottky junction is spread below the junction of the electrode A5, as in FIG. 3 of the first embodiment. The bottom of the conduction band of the semiconductor layer is located above the energy levels of the cathode electrode 4 and the anode electrode C19.

  Therefore, a barrier A13 exists for the movement of electrons from the cathode electrode 4 to the semiconductor layer, and a barrier C20 and a barrier D21 exist for the movement of electrons from the electrode B7 to the semiconductor layer.

  Therefore, it is difficult for electrons to move from the cathode electrode 4 to the electrode C19. In addition, it is difficult for electrons to move from the cathode electrode 4 to the electrode A5 because of the Schottky barrier barrier of the Schottky junction.

  Therefore, at the time of zero bias, current does not flow easily as the whole SBD.

  Next, as shown in FIG. 12, when a positive anode voltage 15 is applied to the anode electrode 8 as a forward bias, the barrier A13 is lowered, so that the electrons 16 move over this, but the electrons flow through the barrier C20. 17 is inhibited.

  However, since the height of the barrier C20 is low, a current flows with a forward bias voltage lower than the rising voltage of the conventional structure.

  Next, as shown in FIG. 13, when a negative anode voltage 18 is applied to the anode electrode 8 as a reverse bias, the conduction band of the electrode C19 moves upward.

  In this case, the electrons 16 do not flow unless they exceed the barrier C20 and further exceed the barrier D21. Since the electrons 16 need to exceed the barrier C20 as compared with the structure of the first embodiment, the reverse current is less likely to flow.

  Therefore, in the present embodiment, the leakage current at the time of reverse bias can be reduced as compared with the first embodiment.

  FIG. 14 shows the structure of the SBD used in the calculation of the embodiment of the present invention in the calculation shown in FIG. 16 to be described later, and FIG. 15 shows the cross-sectional structure of the conventional SBD used for comparison. .

  Unlike the structure used in the first embodiment, the number of the cathode electrodes 4 is one. For this reason, there is only one electrode A5. The small number of electrodes does not have a particularly deep meaning for the effect of the present invention.

  FIG. 16 is a diagram showing the result of calculating the bias voltage dependence of the current characteristics in the first embodiment of the present invention and the SBD of the prior art.

The calculation conditions are as follows: the substrate 1 is a semi-insulating SiC substrate with a thickness of 100 μm, the GaN layer 2 is 0.1 μm in thickness with an N-type impurity concentration of 1E15 cm ⁻³ , the AlGaN layer 3 is 20 nm in thickness, an Al composition is 0.23 and N The type impurity concentration is 1E15 cm ⁻³ , the length of the junction of the electrode A5 is 0.1 μm, the length of the junction of the electrode B7 is 5 μm, and the length of the cathode electrode 4 is 5 μm.

  Similar to the calculation in the first embodiment, in order to extend the depletion layer to the AlGaN layer 3 under the electrode A5, the AlGaN layer under the electrode A5 is made as thin as 5 nm to have a groove (recess) structure.

  The conventional structure used for comparison is the same as that of the present invention except that the electrode A5 having a Schottky junction having a length of 0.1 μm is used as the anode electrode.

  From FIG. 16, it can be seen that in the SBD of the present invention, compared to the case of the first embodiment (FIG. 7), the current at the forward bias is less likely to flow, but the current at the reverse bias is also reduced.

  Further, the SBD of the present invention has a reduced rising voltage and a large current at the time of forward bias compared with the SBD of the prior art, and the effects of the present invention are obtained.

  FIG. 17 is a diagram showing a result of calculating a current density distribution at the time of forward bias (1 V) in the cross section of the SBD (FIG. 14) in the second embodiment of the present invention.

  FIG. 18 is a diagram illustrating a result of calculating a current density distribution at the time of forward bias (1 V) in a cross section (FIG. 15) of the conventional SBD used for comparison.

  In FIGS. 17 and 18, only the vicinity of the electrode A5 in which the Schottky junction is formed is shown as in FIGS. 8 and 9 of the first embodiment.

  17 and 18, as in the first embodiment, in the SBD of the conventional structure, a current flows from the anode electrode 8 to the cathode electrode 4, but in the SBD of the present invention, the current does not pass through the electrode A5 but from the electrode C19 to the cathode. It can be seen that it flows to the electrode 4.

Embodiment 3 FIG.
The third embodiment of the present invention will be described below.

  FIG. 19 is a diagram showing a cross-sectional structure of the SBD in the third embodiment of the present invention.

  The difference from the first embodiment is that the electrode A5 and the electrode B7 (or the electrode C19) are formed in a plane so as to be in direct contact with each other.

  In the above embodiment, the electrode A5 and the electrode B7 (or the electrode C19) are not in direct contact, and a parasitic resistance is generated in the semiconductor layer portion in the region between them (see the parasitic resistance B in FIG. 1).

  In the case of FIG. 1, a parasitic resistance A9 and a parasitic resistance B10 exist in the current path of the cathode electrode 4 and the anode electrode 8.

  In order to ensure the breakdown voltage of the SBD at the time of reverse bias, the distance between the cathode electrode 4 and the electrode A5 is required to be about 0.1 to 100 μm, for example, and therefore the parasitic resistance A has a finite value Ra.

If the value of the parasitic resistance B10 is Rb, the rising voltage of the SBD of the present invention is Vth, and the current at the bias voltage V0 equal to or higher than the rising voltage is K times that of the SBD of the conventional structure,

  If so, a current larger than that of the conventional structure can be obtained at the operating voltage.

  In the first to third embodiments, it is necessary to select the value of the parasitic resistance B10 as determined by the range of the above equation.

  The resistance value Rb can be reduced by increasing the Al composition of the AlGaN layer 3, increasing the film thickness, and shortening the distance between the electrode A5 and the electrode B7 (or electrode C19).

  Among these, the shortening of the distance between the electrode A5 and the electrode B7 (electrode C19) can reduce the parasitic resistance B10 without changing the basic characteristics of the SBD such as the rising voltage. Therefore, as shown in FIG. By directly contacting A5 and the electrode B7 (electrode C19), the parasitic resistance B10 can be reduced, and therefore, an SBD with good characteristics at the time of forward bias can be obtained.

  Further, in the structure of the present embodiment, since the electrode B7 (electrode C19) is in direct contact, the anode electrode 8 does not need to be separately prepared, and the manufacturing cost and the energy consumption during the manufacturing can be reduced. . Further, since the step of the SBD structure can be reduced, the manufacturing yield of SBD itself or wiring is improved.

Embodiment 4 FIG.
Embodiment 4 of the present invention will be described below.

  FIG. 20 is a diagram showing a cross-sectional structure of the SBD in the fourth embodiment of the present invention.

  The difference from the above embodiment is that the electrode B7 (or electrode C19) is formed so as to run over the electrode A5.

  In the third embodiment, the side walls of the electrode A5 and the electrode B7 (or the electrode C19) are in direct contact with each other. However, in such a shape, it is difficult to control the position where the electrode is formed in the manufacturing process.

  In the case of FIG. 20, the electrode A5 is formed, and then the electrode B7 (or electrode C19) is formed so as to cover the electrode A5. Since the electrode B7 (electrode C19) is electrically directly connected as long as it covers the electrode A5, it can be manufactured without precise control of the position accuracy. Further, the step of forming the anode electrode 8 can be omitted.

  FIG. 21 is a modification of the present embodiment. In the figure, contrary to FIG. 20, the electrode B7 (electrode C19) is formed first, and the electrode A5 is formed so as to cover a part thereof.

Embodiment 5. FIG.
Embodiment 5 of the present invention will be described below.

  FIG. 22 is a diagram showing a cross-sectional structure of the SBD in the fifth embodiment of the present invention.

  The difference from the first embodiment is that the electrode B7 (or electrode C19) is also formed in the groove (recess) structure of the AlGaN layer 3, and the junction formation position of the electrode B7 (or electrode C19) is formed deeper than the electrode A5. It is a point.

  Further, the electrode A is formed in the groove (recess) of the AlGaN layer 3 as in the calculations of the first and second embodiments (see FIG. 8).

  In the SBD of FIG. 22, since the distance from the junction interface of the electrode B7 (or the electrode C19) to the heterojunction interface can be shortened, the parasitic resistance of the current path portion in the vertical direction in the figure generated in the AlGaN layer 3 can be reduced. Since the current flowing with the same forward bias voltage increases, the rising voltage can be further reduced.

  Further, since the electrode B7 (or electrode C19) reaches the GaN layer 2, no two-dimensional electron gas is generated in the region, but two-dimensional electrons are directly generated on both sides of the lowermost end of the electrode B7 (or electrode C19). Since it is in contact with the gas generation region, there is no increase in parasitic resistance due to the region where the two-dimensional electron gas is not generated.

  In FIG. 22, the electrode B7 (or electrode C19) reaches the GaN layer 2, but if the junction formation position of the electrode B7 (or electrode C19) is formed deeper than the electrode A5, the parasitic resistance is reduced. Therefore, it is not limited to the structure of the figure.

Embodiment 6 FIG.
Embodiment 6 of the present invention will be described below.

  FIG. 23 is a diagram showing a cross-sectional structure of the SBD in the fifth embodiment of the present invention.

  The difference from the first embodiment is that the AlGaN layer is a P-type AlGaN layer 3a, and an N-type region is formed below the electrode B7 (electrode C19) and below the cathode electrode 4.

  Such a structure is formed, for example, by first forming the P-type AlGaN layer 3a over the entire AlGaN layer and then introducing N-type impurities.

  The electrode A5 and the P-type AlGaN layer 3a are formed under the condition that a Schottky barrier for the electrons 16 is formed.

Although the N ⁺ -AlGaN layer 23 is formed in FIG. 23, it may not be formed as in the above embodiments.

Embodiment 7 FIG.
Hereinafter, a seventh embodiment of the present invention will be described.

  FIG. 24 shows a cross-sectional structure of the SBD in the seventh embodiment of the present invention.

  The difference from the sixth embodiment is that the electrode A5 and the AlGaN layer 3 are formed in the groove (recess) structure of the GaN layer 2, the substrate is the conductive substrate 22, and the cathode electrode. Reference numeral 4 denotes a point formed on the lower side of the substrate 22 in the figure.

  The basic operation principle of the SBD is the same as that of the first embodiment except that the current path from the electrode B7 (electrode C19) to the cathode electrode 4 is different from that of the first embodiment and is in the vertical direction of the drawing. .

  In the present embodiment, since the cathode electrode 4 can be formed on the back side of the substrate by using the conductive substrate 22 as the substrate, the planar size of the SBD can be made smaller than those in the above embodiments.

As shown in the figure, the object of the present invention can be obtained even when the AlGaN layer 3 is between the bottom of the electrode B7 (electrode C19) and the GaN layer 2. In this case, an N ⁺ -GaN layer (not shown) may be formed immediately below B7 (electrode C19).

Embodiment 8 FIG.
Hereinafter, an eighth embodiment of the present invention will be described.

  FIG. 25 shows a cross-sectional structure of the SBD in the eighth embodiment of the present invention.

  The difference from the fourth embodiment is that the electrode A5 is in contact with the GaN layer 2. In the present embodiment, the GaN layer 2 may be either N-type or P-type.

  In the case of the present embodiment, since there is no AlGaN layer 3 below the electrode A5, the barrier A13 (see FIG. 3 or FIG. 11) can be increased, and an SBD characteristic with little current (leakage current) at the time of reverse bias can be obtained. .

  In addition, although the electrode A5 is in contact with the heterojunction interface, the electron gas at the heterojunction interface is depleted due to the presence of the Schottky junction with the GaN layer and the depletion layer, so that it is lower than the rising voltage of the Schottky junction. When the forward bias voltage is applied, the current hardly flows through the electrode A5.

  An insulating film such as SiO, SiN, or AlN may be present between the electrode B7 (electrode C19) and the GaN layer 2, for example, and is not limited to the illustrated structure.

  Moreover, although the figure shows the case where the electrode A5 is formed so as to be in contact with the electrode B7 (electrode C19) in the fourth embodiment, the present invention may be applied to other embodiments.

Embodiment 9 FIG.
The ninth embodiment of the present invention will be described below.

  FIG. 26 is a diagram showing a cross-sectional structure of the SBD in the seventh embodiment of the present invention.

In the figure, 24 is a GaN layer, and 23 is an N ⁺ -GaN layer.

  The difference from the first embodiment is that there is no AlGaN layer 3 and there is an N + GaN layer 23 doped with a high concentration N-type impurity under the cathode electrode 4.

  In this structure, since it is not necessary to deplete the electron gas at the heterojunction interface, the depletion layer tends to spread below the electrode A5, and therefore the current at the time of reverse bias, that is, the leakage current can be further reduced.

  Note that regions having different N-type impurity concentrations can also be formed under the electrode B7 or the electrode C19 to improve ohmic properties and adjust the height of the barrier C20.

Embodiment 10 FIG.
Hereinafter, a tenth embodiment of the present invention will be described.

  In the present embodiment, a structure similar to that of the SBD of the first embodiment (see FIGS. 1 and 2) is used.

  However, in the present embodiment, at the time of reverse bias and zero bias, due to the presence of the depletion layer, the two-dimensional electron gas disappears in a partial region of the heterojunction interface and a discontinuous two-dimensional electron gas region is formed. The In addition, at a forward bias voltage lower than the rise voltage of the Schottky junction (in this case, a voltage as close to zero bias as possible is desirable), the depletion layer in the partial region recedes to generate two-dimensional electron gas at the junction interface. A continuous (or connected) two-dimensional electron gas region is formed. That is, the formation conditions (material, impurity concentration, film thickness, etc.) of the electrode and the semiconductor layer are set so that the region where the electron gas exists is continuous / discontinuous with positive / negative bias voltage.

  For example, at the time of reverse bias and zero bias, the depletion layer reaches the heterojunction interface, depletes electrons and increases the resistance of the current path of the SBD, and at the time of forward bias close to zero bias, the depletion layer does not reach the heterojunction interface In this way, the resistance of the SBD is reduced. Furthermore, the impurity concentration of the semiconductor layer is lowered, and the resistivity near the heterojunction interface when there is no two-dimensional electron gas is increased as compared with the case where there is a two-dimensional electron gas.

  In the SBD formed in this way, at the time of reverse bias and low zero bias, the current path from the cathode electrode to the anode electrode becomes high resistance due to the region where there is no two-dimensional electron gas, so that the current is small.

  Further, as the reverse bias voltage increases, the depletion layer region expands and the two-dimensional electron gas region decreases accordingly, so that the high resistance region expands and current does not flow easily.

  On the other hand, at the time of forward bias, since the two-dimensional electron gas region of the current path is connected and becomes low resistance, a large current flows from a voltage lower than the rising voltage of the Schottky junction as compared with the reverse bias. At a voltage higher than the rising voltage of the Schottky junction, a current flows through the electrode A5 (Schottky junction) as in the first embodiment.

  As described above, nonlinearity occurs in the bias voltage dependency of the SBD operation, and the characteristics as a diode can be obtained. In addition, an SBD with a rising voltage lower than that of the prior art can be obtained.

Embodiment 11 FIG.
In each of the above embodiments, the structure and operation of the single SBD of the present invention have been described. One or more SBDs of the present invention include, for example, an impedance matching circuit, a resistor, and a capacitor for signal input / output as elements of peripheral circuits. The rectifier circuit may be configured by combining some or all of the inductor and the microstrip line for controlling the waveform of the harmonic signal, and the efficiency in rectifying the high-frequency signal is further improved. In that case, various modifications can be made to the mounting form such that the components of the peripheral circuit are integrated on the SBD substrate 1 of the present invention to constitute an IC module.

  In addition, any one or more of the SBD, IC, and IC module related to each of the above embodiments, various electronic devices including a rectifier circuit that uses a diode as a rectifier, for example, a power supply device such as a switching regulator, a non-contact It can be used for a diode or a rectifier circuit such as a portable device with a built-in charger and the signal transmission device RF-DC converter described in Non-Patent Document 1 above.

  Thereby, the power consumption of the various electronic devices can be reduced.

  Note that the circuit configuration of the rectifier circuit and the configurations of the various electronic devices may be a conventionally known configuration such as Non-Patent Document 1 or a new configuration, and are exemplified in the above examples. It is not limited.

  In each of the above embodiments, one electrode A is formed between the cathode electrode 4 and the electrode B7 (or electrode C19), but a plurality of each may be formed together. The form is not limited.

  For example, when the arrangement of the electrodes A and B shown in FIG. 1 is expressed as ABA, a configuration such as ABB ·· BA, ABABA, ABAAABA, or the like is possible.

  When a plurality of the barriers are formed, the barrier A13 and the barrier B14 in FIG. 3 are effectively increased, and the on-resistance of the SBD is increased, but the breakdown voltage is improved. Accordingly, the required barrier height can be adjusted, and an optimum SBD can be used.

  Although the height of the barrier can be adjusted by selecting the metal of the anode electrode, there is a limit. Therefore, the number of electrodes may be adjusted to adjust the height of the barrier.

  In addition, the difference between each embodiment can be applied to other embodiments, and is not limited to the structure of the embodiment.

  For example, the difference between the electrode structures shown in the first to fourth embodiments and the difference between the semiconductor layer structures (including the substrate structure) shown in the fifth and subsequent embodiments can be combined.

  1 substrate, 2 GaN layer (III-V semiconductor layer), 3 AlGaN layer (III-V semiconductor layer), 4 cathode electrode, 5 electrode A (Schottky electrode), 6 protective film (insulating film), 7 electrode B (ohmic electrode), 8 anode electrode, 9 parasitic resistance A, 10 parasitic resistance B, 11 active region, 12 anode voltage (0V), 13 barrier A, 14 barrier B, 15 anode voltage (positive), 16 electrons, 17 Electron flow, 18 anode voltage (negative), 19 electrode C (non-ohmic), 20 barrier C, 21 barrier D, 22 conductive substrate, 23 N + GaN layer, 24 GaN layer

Claims (10)

A substrate,
A III-V group compound semiconductor layer formed on one main surface of the substrate;
A first electrode formed on the III-V compound semiconductor layer and having a Schottky junction formed at a first junction with the III-V compound semiconductor layer;
A Schottky barrier of the Schottky junction is formed on the III-V compound semiconductor layer, and the second junction with the III-V compound semiconductor layer has an ohmic junction or a barrier height at the junction interface. A second electrode formed with a non-ohmic junction having a lower second energy barrier;
A cathode electrode connected to the III-V compound semiconductor layer;
With
The first electrode and the second electrode constitute the same anode electrode,
The first joint is formed between the second joint and the cathode electrode ,
The III-V compound semiconductor layer includes a GaN-based semiconductor layer and an AlGaN-based semiconductor layer formed on the GaN-based semiconductor layer,
(1) The first electrode or the second electrode is formed on the GaN-based semiconductor layer inside the groove of the AlGaN-based semiconductor layer reaching the GaN-based semiconductor layer, or (2) the substrate The AlGaN-based semiconductor layer is formed on the inner surface of the groove and the substrate, and the first electrode is formed on the AlGaN-based semiconductor layer. A Schottky barrier diode characterized by Due to the depletion layer generated in the group III-V compound semiconductor layer with the formation of the first junction, electrons in the group III-V compound semiconductor layer move from the cathode electrode side to the anode electrode side. 2. A Schottky barrier diode according to claim 1, wherein a third energy barrier with respect to and a fourth energy barrier against movement of electrons from the anode electrode side to the cathode electrode side are generated. The III-V group in a region between the first junction and the second junction due to a depletion layer generated in the III-V compound semiconductor layer with the formation of the first junction. 2. The Schottky barrier diode according to claim 1, wherein a region in which an energy level at a bottom of a conduction band of the compound semiconductor layer is above a Fermi level of the cathode electrode and the anode electrode is generated. The III-V group between the cathode electrode and the anode electrode at the time of reverse bias and zero bias is caused by a depletion layer generated in the III-V compound semiconductor layer with the formation of the first junction. The Schottky barrier diode according to claim 1, wherein the resistance of the current path of the compound semiconductor layer is larger than that in forward bias. Both during reverse bias and at zero bias less, by the first depletion layer with the formation of the joint occurring in the Group III-V compound semiconductor layer, and the GaN-based semiconductor layer and the AlGaN based semiconductor layer 2. The Schottky barrier diode according to claim 1 , wherein generation of a two-dimensional electron gas is suppressed at a part of the heterojunction interface. The Schottky barrier diode according to claim 2 , wherein the second energy barrier has a smaller barrier height than the third and fourth energy barriers at zero bias. The Schottky barrier diode according to claim 1, wherein the first electrode and the second electrode are in direct contact. 2. The Schottky barrier diode according to claim 1, wherein a part of the second electrode rides on an upper portion of the first electrode. 2. The Schottky barrier diode according to claim 1, wherein a part of the first electrode rides on an upper part of the second electrode. Electronic device characterized by comprising a rectifying circuit using a schottky barrier diode according as the rectifying element to any one of claims 1 to 9.