CN105261643B - A kind of high-breakdown-voltage GaN base transistor with high electronic transfer rate - Google Patents

Abstract

The invention relates to a gallium nitride based high electron mobility transistor with high breakdown voltage, which mainly consists of substrate, AlN nucleation layer, GaN buffer layer, GaN channel layer, AlGaN barrier layer and The composition of the source, the drain and the gate formed on the barrier layer is characterized in that it also includes an Al _x Ga _1-x N pole with a graded Al composition between the gate and the drain on the AlGaN barrier layer chemically doped layer. The Al composition in the Al _x Ga _1‑x N polarized doped layer increases linearly from top to bottom, and the three-dimensional hole gas generated by the gradual change of the Al composition compensates with the two-dimensional electron gas of the channel to form a self-charged The balanced superjunction structure solves the problem of charge imbalance and improves the breakdown voltage and stability of the device.

Description

A GaN-based High Electron Mobility Transistor with High Breakdown Voltage

technical field

The invention relates to the field of semiconductor devices, in particular to a gallium nitride-based high electron mobility transistor with high breakdown voltage.

Background technique

Gallium nitride (GaN)-based high electron mobility transistor (HEMT) not only has excellent characteristics such as large band gap, high critical breakdown electric field, high electron saturation velocity, good thermal conductivity, radiation resistance and good chemical stability, but also nitrogen Gallium nitride (GaN) materials can also form two-dimensional electron gas (2DEG) heterojunction channels with high concentration and high mobility with materials such as aluminum gallium nitride (AlGaN). Therefore, gallium nitride (GaN)-based high electron mobility transistors are especially suitable for high-voltage, high-power and high-temperature applications, and are one of the most potential transistors for power electronics applications.

However, there is still a large gap between the actual breakdown voltage of GaN devices and the theoretical withstand voltage limit. The main reason is that the problem of gate electric field concentration effect existing in GaN-based high electron mobility transistors is difficult to fundamentally and effectively solve. When the GaN HEMT is under high drain voltage, the channel electric force lines point to the edge of the gate, forming a peak electric field at the edge of the gate. The uneven distribution of the channel electric field causes avalanche breakdown of the device at a lower drain voltage, which cannot Give full play to the high withstand voltage advantages of GaN materials.

In 2011, Nakajima et al. (GaN-based super heterojunction field effect transistors using the polarization junction concept.IEEE Electron Device Letters, 2011,32(4):542-544) proposed a super heterojunction AlGaN/GaN HEMT device to solve Grid electric field concentration effect. The structure of the HEMT device is shown in Figure 1. From bottom to top, there are substrate, GaN buffer layer, GaN channel layer, AlGaN barrier layer, and gate, drain and source formed on the AlGaN barrier layer. A GaN layer and a p-type GaN layer are grown on the AlGaN barrier layer between the gate and the drain. Due to the imbalance of polarization charges at the GaN/AlGaN interface, two-dimensional hole gas (2DHG) will be formed at the GaN/AlGaN interface. The 2DHG mainly comes from the impurity ionization in the p-type GaN layer. When the device withstands the withstand voltage, the 2DHG and the 2DEG in the channel deplete each other, expand the channel electric field area, and smooth the channel electric field distribution, thereby increasing the breakdown voltage of the device.

For GaN materials, magnesium (Mg) doping is usually used to realize p-type GaN materials. Among the p-type impurities of GaN materials, Mg impurities have the lowest activation energy (about 200meV), but it is still much higher than the thermoelectricity at room temperature. Potential (26meV). Excessively high impurity activation energy leads to a very low activation rate of p-type impurities at room temperature (only about 1%), and it will decrease sharply as the temperature decreases, that is, a "freeze-out effect". Therefore, using p-GaN to prepare super-junction GaN HEMT devices not only makes it difficult to ensure device charge balance, but also affects device thermal stability, which limits the withstand voltage capability and application range of GaN devices.

Since 2DEG comes from trap discharges on the surface of the AlGaN barrier layer, 2DEG and 2DHG have different sources, and because of the "freeze-out effect" in P-type GaN materials, it is difficult to achieve charge balance between 2DEG and 2DHG, and the charges in the superjunction are not The balance problem will cause the breakdown voltage to become saturated with the increase of the gate-drain distance, and the high withstand voltage characteristics of GaN materials cannot be fully utilized. In addition, the "freeze-out effect" in the P-type GaN material will also affect the thermal stability of the device. The interfacial traps between the GaN layer and the AlGaN barrier layer due to the stress will lead to the current collapse effect and reduce the reliability of the device.

Contents of the invention

The technical problem to be solved by the present invention is to provide a high breakdown voltage GaN-based high electron mobility solution that can avoid the problems of charge imbalance and poor thermal stability, and can improve its own breakdown voltage. transistor.

The technical solution adopted by the present invention to solve the above technical problems is: a high breakdown voltage GaN-based high electron mobility transistor, which mainly consists of a substrate, an AlN nucleation layer, a GaN buffer layer, and a GaN channel from bottom to top. layer, an AlGaN barrier layer, and a source electrode, a drain electrode, and a gate formed on the AlGaN barrier layer, and is characterized in that it also includes an Al component located on the AlGaN barrier layer, between the gate electrode and the drain electrode Graded AlxGa1 _{- xN} polarized doped layer.

Further, the thickness of the AlxGa1 _{- xN} polarized doped layer is between 50nm and 500nm.

Further, the Al composition on the upper surface of the AlxGa1 _{- xN} polarized doped layer is 0, the Al composition on the lower surface of the AlxGa1 _{- xN} polarized doped layer and the AlGaN barrier layer group The points are the same, increasing linearly from top to bottom.

In order to avoid direct conduction between the drain and the gate through the AlxGa1 _{- xN} polarized doped layer, the AlxGa1 _{- xN} polarized doped layer is connected to the drain, and the AlxGa1 _{- xN} The polarized doped layer and the gate are isolated from each other by an insulating medium; or the Al _x Ga _1-x N polarized doped layer is connected to the gate, and the Al _x Ga _1-x N polarized doped layer is connected to the drain The poles are isolated from each other by an insulating medium; or the Al _x Ga _1-x N polarized doped layer is respectively isolated from the gate and the drain by an insulating medium.

Further, the insulating medium is a high-k medium, the relative permittivity of the high-k medium is greater than 15, and the width of the insulating medium is between 50 nm and 3 μm.

In order to avoid potential floating in the AlxGa1 _{- xN} polarized doped layer and better control device characteristics, a metal electrode is prepared on the AlxGa1 _{- xN} polarized doped layer. Wherein, a Schottky contact or an ohmic contact is formed between the metal electrode and the AlxGa1 _{- xN} polarized doped layer.

Further, the bias voltage of the metal electrode is between the gate bias voltage and the drain bias voltage.

Compared with the prior art, the present invention has the advantage that: in the Al _x Ga _1-x N polarized doped layer, the Al composition increases gradually from top to bottom, so the Al _x Ga _1- x N polarized doped layer The polarization charge density generated by spontaneous polarization and piezoelectric polarization in the dopant layer also changes along the vertical direction. Due to the imbalance of polarization charges, a high concentration of three-dimensional hole gas (3DHG) will be formed in the Al _x Ga _1-x N polarization doped layer. Since the Al composition of the lower surface of the Al _x Ga _1-x N polarized doped layer is the same as that of the AlGaN barrier layer, no interface traps will be formed at the interface, and the device channel 2DEG does not come from the surface traps of the AlGaN barrier layer. At the same time, the 3DHG in the Al _x Ga 1- _x N polarized doped layer will shield the influence of the surface traps of the Al _x Ga _1-x N polarized doped layer on the channel 2DEG, and the channel 2DEG is not derived from Al _x Ga _{1 -x} N polarized doped layer surface trap discharge, but from the 3DHG in the Al _x Ga _1-x N polarized doped layer. According to the principle of electrical neutrality, the 3DHG in the Al _x Ga _1-x N polarized doped layer is equal to the charge of the channel 2DEG, forming a self-balanced superjunction structure of charges, which can effectively solve the problems caused by the lack of charge in the existing superjunction GaN HEMT. The breakdown voltage is too low due to balance; at the same time, there is no "freeze-out effect" in the 3DHG in the Al _x Ga _1-x N polarized doped layer, and the device has better thermal stability. In addition, since the Al composition at the interface between the Al _x Ga _1-x N polarized doped layer and the AlGaN barrier layer is the same, there is no lattice stress at the interface, and no interface traps will be formed; at the same time, 3DHG effectively shields the Al _x Ga _1- The impact of charge and discharge on the surface traps of the _x N polarized doped layer on the channel 2DEG can effectively suppress the current collapse effect and make the device have higher reliability.

Description of drawings

FIG. 1 is a schematic diagram of the structure of a super-junction GaN HEMT in the prior art;

Fig. 2 is a schematic diagram of the GaN HEMT structure in the embodiment of the present invention;

Fig. 3 is a schematic diagram of the energy band structure comparison of the GaN HEMT shown in Fig. 1 with or without surface traps;

Fig. 4 is a schematic diagram of the energy band structure comparison of GaN HEMT with or without surface traps in the embodiment of the present invention;

FIG. 5 is a schematic diagram of a GaN HEMT structure corresponding to improvement measure 1 in the embodiment of the present invention;

FIG. 6 is a schematic diagram of the GaN HEMT structure corresponding to the second improvement measure in the embodiment of the present invention;

FIG. 7 is a schematic diagram of a GaN HEMT structure corresponding to improvement measure 3 in the embodiment of the present invention;

FIG. 8 is a schematic diagram showing the variation of the breakdown voltage with the gate-to-drain distance in the super-junction GaN HEMT shown in FIG. 1 and the GaN HEMT in the present invention.

Among them, the names of parts corresponding to the reference signs in the figure are:

101-substrate, 102-AlN nucleation layer, 103-GaN buffer layer, 104-GaN channel layer, 105-AlGaN barrier layer, 106-source, 107-drain, 108-gate, 109-Al _x Ga _1-x N polarized doped layer, 110—insulation medium between gate and Al _x Ga _1-x N polarized doped layer, 111—drain and Al _x Ga ₁ -x N polarized doped layer Insulation medium between heterogeneous layers, 112—metal electrode.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in FIG. 2 , the GaN-based high electron mobility transistor with high breakdown voltage in this embodiment mainly consists of a substrate 101, an AlN nucleation layer 102, a GaN buffer layer 103, and a GaN channel layer from bottom to top. 104, an AlGaN barrier layer 105, and a source 106, a drain 107, and a gate 108 formed on the AlGaN barrier layer 105. As an improvement, the GaN-based high electron mobility transistor also includes an AlGaN On the barrier layer 105 and between the gate 108 and the drain 107 is formed an Al _x Ga _1-x N polarization doped layer 109 with a graded Al composition.

In this embodiment, the thickness of the AlxGa1 _{- xN} polarized doped layer 109 is between 50nm and 500nm, the Al composition on the upper surface of the AlxGa1 _{- xN} polarized doped layer 109 is 0, and the lower surface The surface Al composition is the same as that of the AlGaN barrier layer 105 and increases linearly from top to bottom.

It can be seen from FIG. 3 that for conventional GaN HEMTs, when the AlGaN barrier layer 105 has no surface traps, the bottom of the conduction band at the interface between the AlGaN barrier layer 105 and the GaN channel layer 104 is higher than the Fermi level, and 2DEG cannot be formed. This shows that the channel 2DEG of the conventional GaN HEMT originates from the surface trap discharge of the AlGaN barrier layer 105 .

It can be seen from Figure 4 that regardless of whether there are surface traps on the surface of the AlxGa1 _{- xN} polarized doped layer 109, the interface between the AlGaN barrier layer 105 and the GaN channel layer 104 can form a 2DEG, which shows that the 2DEG of the HEMT device It does not come from the surface trap discharge, but from the 3DHG generated in the Al _x Ga _1-x N polarized doped layer 109 due to the imbalance of polarized charges. According to the principle of electrical neutrality, 3DHG and 2DEG have the same charge surface density, and the two form a self-balanced superjunction structure. When the device is subjected to withstand voltage, 3DHG and 2DEG are completely depleted each other, which expands the channel depletion region of the device and improves the withstand voltage of the device.

Since the Al composition of the lower surface of the Al _x Ga _1-x N polarized doped layer 109 is the same as the Al composition of the AlGaN barrier layer 105, the Al _x Ga _1-x N polarized doped layer 109, the AlGaN barrier No interface traps are formed at the interface of layer 105 . In addition, the high concentration of 3DHG in the AlxGa1 _{- xN} polarized doped layer 109 can effectively shield the influence of the charge and discharge of surface traps on the AlxGa1 _{- xN} polarized doped layer 109 on the channel 2DEG, thereby inhibiting the device The current collapse effect improves device reliability.

In order to avoid direct conduction between the drain 107 and the gate 108 through the AlxGa1 _{- xN} polarized doped layer 109, as an improvement, the following three measures can be taken: (Improvement 1) AlxGa1 _{- xN} pole The polarized doped layer 109 is connected to the drain 107, and the Al _x Ga _1-x N polarized doped layer 109 is isolated from the gate 108 by an insulating medium 110, as shown in FIG. 5; (improvement measure 2) Al _x The Ga _1-x N polarized doped layer 10 is connected to the gate 108, and the Alx Ga _{1-x N} polarized doped layer 10 is isolated from the drain 107 by an insulating medium 111, as shown in FIG. 6 ; (Improvement Measure 3) Al _x Ga _1-x N polarized doped layer 109 is isolated from gate 108 and drain 107 by insulating medium 110 and insulating medium 111 respectively, as shown in FIG. 7 . Wherein, the insulating medium 110 and the insulating medium 111 in this embodiment are high-k dielectrics, the relative permittivity is greater than 15, and the width is between 50 nm and 3 μm.

On the basis of the improvement measure 3, in order to avoid the potential floating in the AlxGa1 _{- xN} polarized doped layer 109 and better control the device characteristics, the AlxGa1 _{- xN} polarized doped layer 109 A metal electrode 112 is prepared on it. See Figure 7. The metal electrode 112 and the AlxGa1 _{- xN} polarized doped layer 109 may be a Schottky contact or an ohmic contact. Wherein, the bias voltage of the metal electrode 112 is between the bias voltage of the gate 108 and the bias voltage of the drain 107 .

It can be seen from the comparison between the breakdown voltage of the super-junction GaN HEMT and the GaN HEMT in this embodiment with the change of the gate-drain spacing in Fig. The increase of pitch shows a saturation trend, which limits the withstand voltage capability and application range of GaN devices; and the GaNHEMT provided in this embodiment, due to the 3DHG in the AlxGa1 _{- xN} polarization doped layer 109 and the channel 2DEG A charge self-balanced superjunction structure is formed, and the breakdown voltage increases continuously with the increase of the gate-drain distance, which gives full play to the high withstand voltage advantage of GaN material and improves the high withstand voltage capability of the device.

To sum up, in the AlxGa1 _{- xN} polarized doped layer 109, the Al composition gradually increases from top to bottom, so the spontaneous polarization in the AlxGa1 _{- xN} polarized doped layer 109 And the polarization charge density generated by piezoelectric polarization also varies along the vertical direction. Due to the imbalance of polarization charges, a high concentration of three-dimensional hole gas (3DHG) will be formed in the Al _x Ga _1-x N polarization doped layer 109, and the 3DHG will shield the Al _x Ga _1-x N polarization doped layer 109 The effect of surface traps on the channel 2DEG, where the channel 2DEG is not derived from the surface trap discharge of the Al _x Ga 1- _x N polarized doped layer 109, but from the Al _x Ga _1-x N polarized doped layer 109 3DHG inside. According to the principle of electrical neutrality, the 3DHG in the Al _x Ga _1-x N polarized doped layer 109 is equal to the charge of the channel 2DEG, forming a charge self-balancing superjunction structure, which can effectively solve the breakdown caused by the charge imbalance. The voltage is too low; at the same time, the 3DHG in the Al _x Ga _1-x N polarized doped layer 109 does not have the "freeze-out effect", and the device has better thermal stability. In addition, the 3DHG in the AlxGa1 _{- xN} polarized doped layer 109 effectively shields the influence of the charge and discharge of traps on the surface of the AlxGa1 _{- xN} polarized doped layer 109 on the channel 2DEG concentration, thereby suppressing the current Collapse effect, improve device reliability.

Claims (7)

1. a kind of high-breakdown-voltage GaN base transistor with high electronic transfer rate, from bottom to up successively mainly by substrate (101), AlN nucleating layers (102), GaN cushions (103), GaN channel layers (104), AlGaN potential barrier (105) and in AlGaN potential barriers Source electrode (106), drain electrode (107) and grid (108) composition formed on layer (105), it is characterised in that further include positioned at AlGaN The Al of Al content gradually variationals on barrier layer (105), between grid (108) and drain electrode (107)_xGa_1-xN polarization doped layers (109)；The Al_xGa_1-xThe upper surface Al components of N polarization doped layers (109) are 0, Al_xGa_1-xUnder N polarization doped layers (109) Surface A l components are identical with AlGaN potential barrier (105) component, from top to bottom linear increase.

2. high-breakdown-voltage GaN base transistor with high electronic transfer rate according to claim 1, it is characterised in that described Al_xGa_1-xThe thickness of N polarization doped layers (109) is between 50nm~500nm.

3. high-breakdown-voltage GaN base transistor with high electronic transfer rate according to claim 1, it is characterised in that described Al_xGa_1-xN polarization doped layers (109) are connected with drain electrode (107), Al_xGa_1-xBetween N polarization doped layers (109) and grid (108) It is mutually isolated by dielectric.

4. high-breakdown-voltage GaN base transistor with high electronic transfer rate according to claim 1, it is characterised in that described Al_xGa_1-xN polarization doped layers (109) are connected with grid (108), Al_xGa_1-xBetween N polarization doped layers (109) and drain electrode (107) It is mutually isolated by dielectric.

5. high-breakdown-voltage GaN base transistor with high electronic transfer rate according to claim 1, it is characterised in that described Al_xGa_1-xN polarization doped layers (109) are mutually isolated by dielectric with grid (108), drain electrode (107) respectively；It is described Al_xGa_1-xBeing prepared on N polarization doped layers (109) has metal electrode (112)；The bias voltage of the metal electrode (112) between Between grid (108) bias voltage, drain electrode (107) bias voltage.

6. high-breakdown-voltage GaN base transistor with high electronic transfer rate according to claim 5, it is characterised in that described Dielectric is high K medium, and the relative dielectric constant of high K medium is more than 15, the dielectric width be in 50nm~3 μm it Between.

7. high-breakdown-voltage GaN base transistor with high electronic transfer rate according to claim 6, it is characterised in that described Metal electrode (112) and Al_xGa_1-xSchottky contacts or Ohmic contact are formed between N polarization doped layers (109).