JP2005045292A - METHOD OF FABRICATING p-TYPE GROUP III NITRIDE COMPOUND SEMICONDUCTOR, METHOD OF FABRICATING LIGHT EMITTING DIODE AND METHOD OF FABRICATING SEMICONDUCTOR LASER - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a crystal property and electrical conductivity and also uniform the composition ratio and the p-type impurity concentration in a growth surface of a crystal. <P>SOLUTION: First layers 11 of about 1 to 100 nm in thickness formed of AlGaN mixed crystal each and second layers 12 of about 1 to 100 nm in thickness formed of Mg doped p-type GaN each are stacked alternately to stack a plurality of layers. The first layers 11 and the second layers 12 that have aluminum contents and p-type impurity concentrations different from each other are formed in separate processes to enable fabricating a satisfactory p-type group III nitride compound semiconductor that has a property of p-type AlGaN mixed crystal as a whole. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to at least one group III element in the group consisting of gallium (Ga), aluminum (Al), boron (B) and indium (In), nitrogen (N), magnesium (Mg), zinc The present invention relates to a method for producing a p-type group III nitride compound semiconductor, a method for producing a light emitting diode, and a method for producing a semiconductor laser, including at least one p-type impurity selected from the group consisting of (Zn) and carbon (C).

  In recent years, group III nitride compound semiconductors such as GaN, AlGaN mixed crystals, InGaN mixed crystals, or BAlGaInN mixed crystals are promising as materials constituting them in fields such as short wavelength light source elements, environmental resistance elements, and high frequency electronic elements. ing. Recently, a light emitting diode (LED) using this group III nitride compound semiconductor has been put into practical use and attracting attention. In addition, achievement of a semiconductor laser (LD) has been reported, and applications such as optical disks are expected.

  When such a device is put to practical use, it is important to efficiently produce a high-quality group III nitride compound semiconductor that can be used as a device. In particular, in an optical device, it is desired to produce high-quality p-type and n-type group III nitride compound semiconductors in order to confine light and electrons in holes and to allow current to flow efficiently.

Incidentally, as a method for producing a group III nitride compound semiconductor, there are a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE), and the like. For example, in the MOCVD method, a source gas (organic metal gas) of a group III element such as germanium, aluminum, and indium is supplied onto a heated substrate together with a nitrogen source gas (for example, ammonia (NH ₃ ) gas), and reacted. A group III nitride compound semiconductor is epitaxially grown on the substrate. In the MBE method, a group III element and nitrogen particle beam is irradiated on the substrate, and a group III nitride compound semiconductor is epitaxially grown on the substrate.

  At this time, if an n-type semiconductor is to be manufactured, a source gas or particle beam of an n-type impurity such as silicon (Si) is supplied together with a group III element and nitrogen source gas or particle beam. As a result, an n-type group III nitride compound semiconductor having high crystallinity and electrical conductivity can be easily produced. On the other hand, if a p-type semiconductor is to be produced, a crystal is grown by supplying a source gas or particle beam of a p-type impurity such as magnesium, zinc or carbon together with a group III element and nitrogen source gas or particle beam. After that, carriers are activated by low-energy electron beam irradiation, thermal annealing, or the like as necessary.

  However, an n-type group III nitride compound semiconductor can be easily manufactured, whereas a p-type group III nitride compound semiconductor is difficult to manufacture and has low crystallinity and electrical conductivity. In the growth plane (in the plane parallel to the surface of the substrate), the composition ratio and the p-type impurity concentration become non-uniform. This is presumably because the group III element source gas or particle beam reacts with the p-type impurity source gas or particle beam before reaching the substrate.

  In particular, it is difficult to produce a p-type AlGaN mixed crystal to which magnesium is added as a p-type impurity, and the aluminum composition of the AlGaN mixed crystal as a base crystal is significantly lower than that in the case where magnesium is not added. As a result, the electrical characteristics are significantly inferior to those of GaN to which the same level of magnesium is added. That is, among group III elements, it is considered that aluminum and the p-type impurity magnesium are particularly likely to react.

As a prior art of the present invention, for example, there is a nitride semiconductor element described in Patent Document 1. This nitride semiconductor device lowers the threshold current and voltage by forming a superlattice layer with a two-layer structure having different compositions. However, the impurity concentration of a layer with a large bandcap energy is increased. It has a configuration different from that of the invention.
JP-A-10-335757

  The present invention has been made in view of such problems, and the object thereof is a p-type group III nitride having high crystallinity and electrical conductivity, and having a uniform composition ratio and p-type impurity concentration in the crystal growth plane. An object of the present invention is to provide a compound semiconductor manufacturing method, a light emitting diode manufacturing method, and a semiconductor laser manufacturing method.

  The method for producing a p-type group III nitride compound semiconductor according to the present invention includes a step of forming a first layer containing aluminum, gallium and nitrogen, and adding magnesium to the first layer at a relatively low concentration. Forming a second layer containing gallium and nitrogen, and adding a relatively high concentration of magnesium to the second layer to form a layer having a lower resistance than the first layer, A plurality of first layers and second layers are alternately formed.

  Each manufacturing method of the light emitting diode and the semiconductor laser of the present invention also includes the manufacturing process of the p-type group III nitride compound semiconductor of the present invention.

  In the method for producing a p-type group III nitride compound semiconductor according to the present invention, a plurality of first layers and a second layer having a lower resistance value are alternately formed. It has a function as a type III group nitride compound semiconductor.

  According to the method for manufacturing a p-type group III nitride compound semiconductor, light emitting diode, or semiconductor laser of the present invention, the first layer containing aluminum, gallium and nitrogen is formed, and magnesium is relative to the first layer. And adding a relatively high concentration of magnesium to the second layer and forming a second layer containing gallium and nitrogen, and forming a second layer containing gallium and nitrogen. A plurality of first layers and second layers are alternately formed, so that a plurality of p-type group III nitride compound semiconductors as a whole are formed in the plurality of layers. It is possible to provide functions, and the crystallinity of each layer can be easily increased. Thus, the overall crystallinity and electrical conductivity can be improved, and the uniformity of the composition and p-type impurity concentration in the growth plane can be improved. Therefore, if this p-type group III nitride compound semiconductor is used to construct a short wavelength light source element such as a light emitting diode and a semiconductor laser, an environment resistant element, a high frequency electronic element, etc., the quality can be improved. Play.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a p-type group III nitride compound semiconductor according to an embodiment of the present invention. This p-type group III nitride compound semiconductor is obtained by adding magnesium as a p-type impurity to a base crystal composed of aluminum and gallium and nitrogen, which are group III elements. However, this p-type group III nitride compound semiconductor does not have a uniform composition or type of group-III element and p-type impurity concentration throughout, and the first layer 11 and the second layer are different from each other. 12 are alternately provided in a plurality of layers.

  For example, as illustrated in parentheses in FIG. 1, the first layer 11 is made of AlGaN mixed crystal, and the second layer 12 is made of p-type GaN containing magnesium as a p-type impurity. That is, the p-type group III nitride compound semiconductor includes a first layer 11 that includes aluminum but does not include magnesium, and aluminum that includes magnesium, among the group III element aluminum and p-type impurity magnesium. The second layers 12 not included are alternately stacked.

  Although not illustrated in FIG. 1, the first layer 11 is composed of a magnesium-containing p-type AlGaN mixed crystal having a p-type impurity concentration lower than that of the second layer 12 and a higher group III element aluminum composition ratio. The second layer 12 may be composed of a magnesium-containing p-type AlGaN mixed crystal having a higher p-type impurity concentration and a lower aluminum composition ratio than the first layer 11. In other words, the p-type group III nitride compound semiconductor has alternating first layers 11 containing more aluminum than the second layers 12 and second layers 12 containing more magnesium than the first layers 11. Are laminated.

  The thicknesses of the first layer 11 and the second layer 12 are each about 1 to 100 nm, for example. Thus, since the thickness of the 1st layer 11 and the 2nd layer 12 is thin, respectively, the p-type group III nitride compound semiconductor which concerns on this Embodiment has the 1st layer 11 and magnesium which do not contain magnesium. Even if the second layer 12 not included is laminated, it can have the property of a p-type AlGaN mixed crystal as a whole. Further, even if the first layer 11 and the second layer 12 having different magnesium concentrations and different aluminum composition ratios are stacked, the layer as a whole has properties as one p-type AlGaN mixed crystal. it can. Incidentally, the thickness of the first layer 11 and the second layer 12 may or may not be the same.

  The p-type group III nitride compound semiconductor having such a configuration can be manufactured as follows.

  First, an appropriate substrate (for example, a sapphire substrate) is prepared, and an AlGaN mixed crystal layer to which magnesium is not added as the first layer 11 and magnesium as the second layer 12 by an MOCVD method or MBE method in an appropriate furnace. The p-type GaN layers to which is added are alternately stacked (stacking step).

For example, in the case of the MOCVD method, an appropriate source gas is selectively supplied into the furnace together with a carrier gas while appropriately heating the substrate (for example, 800 to 1000 ° C.), and each crystal layer is grown on the substrate. For example, trimethylaluminum gas ((CH ₃ ) ₃ Al) is used as the source gas for aluminum, trimethylgallium gas ((CH ₃ ) ₃ Ga) is used as the source gas for gallium, and ammonia gas and magnesium source are used as the source gas for nitrogen. As the gas, bis = methylcyclopentadienyl magnesium gas (MeCp ₂ Mg) or bis = cyclopentadienyl magnesium gas (Cp ₂ Mg) is used. As the carrier gas, hydrogen gas (H ₂ ), nitrogen gas (N ₂ ), or the like is used. When growing an AlGaN mixed crystal layer, source gases of aluminum, gallium and nitrogen are selectively supplied among source gases, and when a p-type GaN layer is grown, source gases of magnesium, gallium and nitrogen are selectively supplied. To do.

  In the case of the MBE method, each crystal beam is grown by selectively irradiating the substrate with aluminum, gallium, nitrogen and magnesium particle beams.

  After the first layer 11 and the second layer 12 are grown in this manner, heat treatment is performed as necessary. As a result, aluminum in the first layer 11 (AlGaN mixed crystal layer) and magnesium in the second layer 12 (p-type GaN layer) partially diffuse with each other. Therefore, when this heat treatment is performed, the first layer 11 becomes a p-type AlGaN mixed crystal layer with a low magnesium concentration and a high aluminum composition ratio, and the second layer 12 has a high magnesium concentration and an aluminum composition ratio. It becomes a low p-type AlGaN mixed crystal layer. As described above, the p-type group III nitride compound semiconductor according to the present embodiment is formed.

  Thus, according to the p-type group III nitride compound semiconductor according to the present embodiment, the first layer 11 made of AlGaN mixed crystal and the second layer 12 made of p-type GaN containing magnesium as a p-type impurity, The first layer 11 made of a p-type AlGaN mixed crystal slightly containing magnesium and the second layer 12 made of a p-type AlGaN mixed crystal containing slightly aluminum are provided. Since a plurality of layers are alternately provided, the crystallinity of the first layer 11 and the second layer 12 can be easily increased. Therefore, it is possible to improve the crystallinity and electrical conductivity while giving the properties as a p-type AlGaN mixed crystal as a whole, and to improve the uniformity of the composition and p-type impurity concentration in the growth plane. it can.

  In addition, according to the method of manufacturing the p-type group III nitride compound semiconductor according to the present embodiment, the AlGaN mixed crystal layer as the first layer 11 and the p-type GaN layer as the second layer 12 are alternately formed. Since the layers are stacked, it is possible to supply the aluminum raw material and the magnesium raw material, which cannot grow a good crystal if they are supplied at the same time, separated in time, and have a high crystallinity or electrical conductivity. The first layer 11 and the second layer 12 having a uniform composition or uniform p-type impurity concentration can be formed. Therefore, a good p-type group III nitride compound semiconductor having properties as a p-type AlGaN mixed crystal as a whole can be easily manufactured.

  Furthermore, the present invention will be described with specific examples.

  In this embodiment, first, as shown in FIG. 2, a buffer layer 22 made of GaN having a thickness of about 20 nm and a GaN layer 23 having a thickness of about 1 μm are formed on a substrate 21 made of sapphire, and on that, The first layer 11 made of AlGaN mixed crystal having a thickness of 10 nm and the second layer 12 made of p-type GaN added with magnesium having a thickness of 10 nm were alternately stacked in 20 layers.

  Each of these layers was formed by MOCVD as shown in FIG. That is, the substrate 21 was mounted on a mounting table 32 provided inside an appropriate reaction furnace 31, and the source gas was allowed to flow in parallel with the surface of the substrate 21 (ie, the growth surface) together with the carrier gas. The substrate 21 was heated to 1000 ° C. by a heating device (not shown) provided on the mounting table 32.

  Incidentally, trimethylaluminum gas is used for the aluminum source gas, trimethylgallium gas is used for the gallium source gas, ammonia gas is used for the nitrogen source gas, and bis = methylcyclopentadienylmagnesium gas is used for the magnesium source gas. Each was used and selectively fed into the furnace according to the layer to be grown. That is, when the first layer 11 is grown, trimethylaluminum gas, trimethylgallium gas, and ammonia gas are supplied, and when the second layer 12 is grown, bis = methylcyclopentadienylmagnesium gas and Trimethylgallium gas and ammonia gas were respectively supplied. Moreover, hydrogen gas and nitrogen gas were used for carrier gas.

  Next, heat treatment for activating the carrier was performed. Thus, a sample of this example was produced.

  After that, regarding the prepared sample, the composition ratio of aluminum averaged over the entire stacking direction of the first layer 11 and the second layer 12 was analyzed by X-ray diffraction. The analysis was performed for a plurality of positions (three points on the center, upstream side, and downstream side) in the growth surface of the sample. The analysis result is shown in FIG. 4 in comparison with the conventional example. In the conventional example, instead of the first layer 11 and the second layer 12 of this embodiment, source gases of aluminum, gallium, nitrogen and magnesium are simultaneously supplied to form a p-type AlGaN mixed crystal layer. Except for the above, it was fabricated in the same manner as in this example.

  As can be seen from FIG. 4, in the conventional example, the composition ratio of aluminum is large on the upstream side of the raw material gas, and rapidly decreases from the center to the downstream side. This is presumably because the aluminum and magnesium source gases reacted upstream and the composition ratio of aluminum in the growth plane became non-uniform. In contrast, in this example, the difference in the aluminum composition ratio depending on the position of the sample was small, and the aluminum composition ratio was high on average. That is, according to this example, it was found that the crystallinity and the uniformity of the composition in the growth plane were improved as compared with the conventional example.

Further, the carrier concentration of the produced sample was measured and found to be 1 to 3 × 10 ¹⁷ cm ⁻³ . Although the carrier concentration was tried to be measured for the conventional example as well, the resistance was high, and even if an electrode was installed, ohmic contact could not be obtained and measurement was impossible. That is, according to this example, it was found that the electrical conductivity was improved as compared with the conventional example.

  While the present invention has been described with reference to the embodiments and examples, the present invention is not limited to these embodiments and examples, and various modifications can be made within the equivalent range. For example, in the above embodiment and the above example, a p-type group III nitride compound semiconductor in which magnesium as a p-type impurity is added to a base crystal composed of group III elements aluminum and gallium and nitrogen has been described. The present invention includes at least one group III element in the group consisting of gallium, aluminum, boron and indium, nitrogen, and at least one p-type impurity in the group consisting of magnesium, zinc and carbon. The present invention can be widely applied to p-type group III nitride compound semiconductors.

  In the manufacturing process, in the stacking step, at least one of group III elements is included only in the first layer of the first layer and the second layer, and at least one of the p-type impurities. A plurality of first layers and second layers that include seeds only in the second layer of the first layer and the second layer may be alternately stacked.

  In the above embodiment, the p-type group III nitride compound semiconductor is constituted by the first layer 11 and the second layer 12. However, the present invention relates to the first layer 11 and the second layer 12. In addition to the layer 12, other layers may be provided. For example, in the above embodiment, when Al in the first layer 11 (AlGaN mixed crystal layer) and magnesium in the second layer 12 (p-type GaN layer) diffuse in a very narrow range by heat treatment, the AlGaN mixed crystal A third layer made of a p-type AlGaN mixed crystal may be provided between the first layer 11 made of p-type GaN and the second layer 12 made of p-type GaN.

  Further, in the above embodiment and the above examples, the case where the p-type group III nitride compound semiconductor of the present invention is manufactured using the MOCVD method or the MBE method has been described. However, the present invention uses other methods. The present invention can also be widely applied to the manufacturing process.

It is a block diagram of the p-type group III nitride compound semiconductor which concerns on one embodiment of this invention. It is a block diagram of the sample grown by MOCVD method in one Example of this invention. It is explanatory drawing at the time of growing the sample shown in FIG. 2 by MOCVD method. It is a characteristic view showing the relationship between the position in the growth surface of the sample produced in the Example of this invention, and the composition ratio of aluminum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... 1st layer, 12 ... 2nd layer, 21 ... Substrate, 22 ... Buffer layer, 23 ... GaN layer, 31 ... Reactor, 32 ... Mounting stand

Claims (6)

Forming a first layer comprising aluminum, gallium and nitrogen and adding magnesium to the first layer at a relatively low concentration;
Forming a second layer containing gallium and nitrogen, and adding magnesium to the second layer at a relatively high concentration to form a layer having a lower resistance than the first layer,
A method for producing a p-type group III nitride compound semiconductor, wherein a plurality of the first layers and the second layers are alternately formed.
2. The method of manufacturing a p-type group III nitride compound semiconductor according to claim 1, wherein the first layer is AlGaN and the second layer is GaN.
A method of manufacturing a light emitting diode composed of a p-type group III nitride compound semiconductor,
The manufacturing process of the p-type group III nitride compound semiconductor comprises:
Forming a first layer comprising aluminum, gallium and nitrogen and adding magnesium to the first layer at a relatively low concentration;
Forming a second layer containing gallium and nitrogen, and adding magnesium to the second layer at a relatively high concentration to form a layer having a lower resistance than the first layer,
A method of manufacturing a light-emitting diode, wherein a plurality of first layers and second layers are alternately formed.
4. The light emitting diode manufacturing method according to claim 3, wherein the first layer is AlGaN, and the second layer is GaN.
A method for producing a semiconductor laser comprising a p-type group III nitride compound semiconductor,
The manufacturing process of the p-type group III nitride compound semiconductor comprises:
Forming a first layer comprising aluminum, gallium and nitrogen and adding magnesium to the first layer at a relatively low concentration;
Forming a second layer containing gallium and nitrogen, and adding magnesium to the second layer at a relatively high concentration to form a layer having a lower resistance than the first layer,
A method of manufacturing a semiconductor laser, wherein a plurality of first layers and second layers are alternately formed.
6. The method of manufacturing a semiconductor laser according to claim 5, wherein the first layer is AlGaN, and the second layer is GaN.

Images