JP3555512B2 - Method for producing p-type gallium nitride-based compound semiconductor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a p-type compound semiconductor. The present invention relates to a method for producing a p-type gallium nitride-based compound semiconductor for a light-emitting device such as an ultraviolet ray, a blue light-emitting diode and a laser diode, or for a gallium nitride-based electronic device having a p-type layer. The present invention relates to a method of forming a gallium nitride-based compound semiconductor layer formed by doping a p-type impurity by a growth method into a p-type layer having a high carrier concentration.
[0002]
[Prior art]
Research on ultraviolet and blue light-emitting elements using gallium nitride (GaN) -based compound semiconductors has been widely conducted. As a method for forming and laminating such a gallium nitride (GaN) -based semiconductor layer, there are known methods such as metal organic chemical vapor deposition (hereinafter referred to as MOCVD) and molecular beam epitaxy (hereinafter referred to as MBE). Phase growth methods are well known.
[0003]
The MOCVD method will be briefly described below as an example of such a vapor phase growth method, and the technical background will be clarified. That is, in this method, a group III organic metal compound and a group V source gas (eg, trimethylgallium (TMG), trimethylaluminum (TMA), ammonia, etc.) are heated and held on a substrate (eg, sapphire, SiC, etc.). And a gallium nitride-based compound semiconductor is grown on the substrate. Further, if necessary, by supplying another impurity gas at this time, n-type, i-type, and p-type conductivity can be provided. As such impurities, Si is well known as an n-type impurity, and Zn and Mg are often used as p-type impurities. However, a p-type impurity doping alone to grow a crystal does not make it possible to obtain a p-type gallium nitride-based compound semiconductor having a high carrier concentration and a high-resistance semi-insulating material having a resistivity of 10 ⁸ Ω · cm or more. A material, that is, an i-type material is obtained.
[0004]
Attempts have been made in the past to reduce the resistance of such a high-resistance i-type body to approach the p-type.
[0005]
In JP-A-2-257679, a high-resistance i-type gallium nitride-based compound semiconductor doped with Mg as a p-type impurity is formed in an uppermost layer, and the surface of the Mg-doped gallium nitride-based compound semiconductor in the uppermost layer is It describes a method of irradiating an electron beam with an acceleration voltage of 6 kV to 30 kV to thereby lower the resistance of a layer of about 0.5 μm from the surface. However, in such a method, only the very surface portion where the electron beam enters is reduced in resistance, and the entire wafer must be irradiated by scanning the electron beam. It was not possible to lower the resistance uniformly.
[0006]
Further, in Japanese Patent Application Laid-Open No. 5-183189, a compound semiconductor doped with a p-type impurity is similarly subjected to a heat treatment, whereby the bond between the hydrogen atom in the crystal and the p-type impurity is cut off, and the p-type impurity is uniformly dispersed in the plane. A method for activating impurities is described. However, with such a method, a compound semiconductor having a practically sufficient carrier concentration could not be obtained.
[0007]
[Problems to be solved by the invention]
As understood from the above description, the carrier concentration of the p-type gallium nitride-based compound semiconductor obtained by the conventional technique was insufficient to form an ohmic contact by bringing the same into contact with a metal.
[0008]
An object of the present invention is to produce a p-type gallium nitride-based compound semiconductor having a low resistance and a high carrier concentration by treating a gallium nitride-based compound semiconductor doped with a p-type impurity.
[0009]
[Means for Solving the Problems]
In the method for producing a p-type gallium nitride-based compound semiconductor of the present invention, a gallium nitride-based compound semiconductor doped with a p-type impurity is formed by a vapor phase growth method, and when heat-treated at a temperature of 400 ° C. or more, hydrogen is absorbed. Heat treatment is basically performed in the presence of a metal or an alloy having the ability to perform the heat treatment.
[0010]
As the metal or alloy having the ability to occlude hydrogen used in the present invention, simple metals such as Ti, Zr and Ni and alloys thereof are known, but any metal or (and) alloy may be used. Good.
[0011]
In the method of the present invention, the atmosphere for the heat treatment of the gallium nitride-based compound semiconductor doped with the p-type impurity is preferably an atmosphere containing no hydrogen gas or a vacuum. The reason why the atmosphere or the like containing no hydrogen gas is preferable is that the activation of the p-type impurity is performed by dehydrogenation, and the atmosphere containing hydrogen (H ₂ ) and a hydrogen compound (H ₂ O, ammonia, etc.) is used. It is not preferable to perform the heat treatment in the inside.
[0012]
Similarly, at the time of heat treatment, heat treatment is performed together with a gallium nitride-based compound semiconductor doped with a p-type impurity and a metal or an alloy having the ability to occlude hydrogen. Although it does not matter, it is preferable that a heat treatment is performed by bringing a gallium nitride-based compound semiconductor doped with a p-type impurity into contact with a metal or an alloy that stores hydrogen, since a p-type gallium nitride crystal with a higher carrier concentration can be obtained. . In the heat treatment, the heat treatment temperature is preferably set to 800 ° C. or lower, for the purpose of preventing sublimation and decomposition of the gallium nitride crystal.
[0013]
The metal or alloy capable of storing hydrogen in the method of the present invention promotes the activation of p-type impurities and provides a higher activation rate than a simple heat treatment.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0015]
FIG. 1 is a schematic diagram of an annealing apparatus used for heat-treating a gallium nitride-based compound semiconductor doped with a p-type impurity in the method of the present invention.
[0016]
FIG. 2 is a view showing a sample stage of an annealing apparatus for heat-treating a gallium nitride-based compound doped with a p-type impurity and a metal or an alloy having a hydrogen storage capacity side by side without contacting each other in the method of the present invention. FIG. 2 is a schematic explanatory view showing one example, in which an upper figure shows a state where the sample table is viewed from above, and a lower figure shows a schematic cross section of the sample table.
[0017]
FIG. 3 is a diagram showing a sample stage of an annealing apparatus for heat-treating a gallium nitride-based compound semiconductor doped with a p-type impurity and a metal or an alloy having a hydrogen storage ability by overlapping and contacting each other in the method of the present invention. FIG. 7 is a schematic explanatory view showing another example, in which an upper figure shows a state where the sample table is viewed from above, and a lower figure shows a schematic cross section of the sample table.
[0018]
As shown in FIG. 1, the annealing apparatus includes a quartz tube 1, a sample transfer rod inlet 2 and an exhaust port (connected to a vacuum pump) provided therein, a heater 5 for heating the quartz tube 1, and a sample transfer. A sample transport rod 3 inserted from the rod inlet 2 and a sample table 4 attached to the sample transport rod 3 are provided. The sample stage 4 is for heat-treating a gallium nitride-based compound semiconductor doped with a p-type impurity and a metal or alloy having an ability to occlude hydrogen, according to FIG. 2 or FIG. Details are shown.
[0019]
In the sample stage 4 shown in FIG. 2, the sample stage 4 has a groove 8 for a GaN-based compound semiconductor for holding a gallium nitride-based compound semiconductor, and a metal or an alloy having an ability to absorb hydrogen independently of the groove 8. A groove 9 for a hydrogen-absorbing alloy for holding the GaN-based compound semiconductor, and a GaN-based compound semiconductor 10 doped with a p-type impurity is held in the groove 8 for the GaN-based compound semiconductor during the heat treatment. The hydrogen storage alloy groove 9 holds a hydrogen storage alloy (a metal or an alloy capable of storing hydrogen) 11.
[0020]
In the sample stage 4 shown in FIG. 3, the sample stage 4 is provided for stacking a GaN-based compound semiconductor 10 and a metal or alloy (hydrogen storage alloy) 11 having an ability to occlude hydrogen and for holding them in contact with each other. A groove 12 for a sample is provided, and the groove 12 for the sample is provided with a GaN-based compound semiconductor 10 doped with a p-type impurity and a metal or an alloy capable of absorbing hydrogen (hydrogen storage alloy) during heat treatment. 11 are held in contact with each other.
[0021]
Regarding the metal or alloy having the ability to occlude hydrogen used in the method of the present invention, the case of Zr is shown in the following examples, and Ti and Ni are exemplified above as examples other than Zr. examples, Mg, La, U, Pd , elemental metals of V, _{etc., LaNi 5, FeTi, Mg 2} Ni, Mg 2 Cu, TiCo, ZrMn 2, LaCo 5, CaNi 5, MnNi 5, Ti 2 such as Mn Alloys.
[0022]
【Example】
(Formation of gallium nitride film doped with p-type impurity)
First, trimethylgallium (TMG) is used as a Ga source, biscyclopentagenenyl magnesium (Cp ₂ Mg) is used as a Mg source, and ammonia (NH ₃ ) is used as an N source, and these are respectively formed on a sapphire substrate by MOCVD. A gallium nitride (GaN, hereinafter referred to as GaN) film was supplied and doped with a p-type impurity.
[0023]
In the following Examples and Comparative Examples, the GaN doped with the p-type impurity obtained above was placed on a sample stage in a quartz tube (see FIG. 1) which was made to be heated by a prepared heater. (FIG. 3) heat treatment by contacting zirconium (Zr) as a metal having the ability to occlude GaN and zirconium doped with p-type impurities on a sample stage without contact A method of producing a p-type GaN-based semiconductor by a method (comparative example) in which only GaN doped with p-type impurities is similarly placed on a sample stage (see FIG. 2) and a heat treatment will be described.
[0024]
(Comparative example)
Using the apparatus described above, a sample cut from a wafer of GaN doped with the p-type impurity obtained above (the sample used in Examples 1-3 below was also doped with the same p-type impurity. GaN wafer cut from the GaN wafer) was heat-treated at a heat treatment temperature of 700 ° C. and a degree of vacuum of 100 Pa without using a metal or an alloy capable of absorbing hydrogen. As a result, p-type GaN having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ was obtained.
[0025]
(1 of Example 1)
Using a device similar to that of the comparative example, a sample cut out of a GaN wafer doped with the same p-type impurity as described above, and zirconium (Zr, hereinafter referred to as Zr) as a metal capable of absorbing hydrogen. As shown in FIG. 2, a heat treatment was performed under the same conditions as in the comparative example in a state where the GaN sample and Zr were arranged side by side without contact with each other on the sample table. As a result, p-type GaN having a carrier concentration of 8 × 10 ¹⁷ cm ⁻³ was obtained.
[0026]
(Example 1-2)
FIG. 3 shows a sample cut from a GaN wafer doped with the same p-type impurity as described above and Zr as a metal capable of absorbing hydrogen, using the same apparatus as the comparative example. As described above, the GaN sample was placed on the sample table, and the Zr was placed thereon and heat-treated under the same conditions as in the comparative example, with the Zr being in contact with each other. As a result, p-type GaN having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ was obtained.
[0027]
However, when GaN and Zr are contacted and heat-treated as described above, surface treatment of GaN is required after heat treatment because Zr is attached to the GaN surface. As such a surface treatment method, aqua regia cleaning was used. Thereby, Zr is removed from the surface.
[0028]
From the results of Example 1 and Comparative Example, during the heat treatment of GaN, by contacting GaN and a metal such as Zr capable of absorbing hydrogen, the activation of p-type impurities present in the GaN crystal was promoted, It has also been found that a higher carrier concentration can be realized.
[0029]
(Example 2)
Using the same apparatus as in the comparative example, the GaN sample and Zr as described above were heat-treated in a vacuum of 100 Pa so that Zr was placed on the GaN sample on the sample stage and brought into contact with each other as shown in FIG. Then, the heat treatment temperature dependence of the p-type carrier concentration in a vacuum of 100 Pa was examined. The result is shown in FIG.
[0030]
As shown in FIG. 4, it is clear that the heat treatment at 400 ° C. or more activates the p-type impurities. Further, it is clear that the higher the heat treatment temperature, the higher the p-type carrier concentration.
[0031]
However, measurement was not possible when the heat treatment temperature was lower than 400 ° C. or 700 ° C. or higher. It is considered that the reason is that at temperatures lower than 400 ° C., p-type carriers are not generated, and at temperatures higher than 700 ° C., GaN is decomposed and sublimated to deteriorate the crystal surface state, This is probably because the ohmic electrode could not be formed. Such a reason is presumed from the fact that a metallic luster considered to be metallic Ga was observed on the GaN surface after the heat treatment.
[0032]
(Example 3)
Using the same apparatus as the comparative example, as shown the such GaN samples and Zr in the Figure 3, in the as to brought into contact with each other and put the Zr on the GaN sample on the sample stage, the N ₂ is used as the atmospheric gas The pressure dependence of the p-type carrier concentration was examined at a heat treatment temperature of 700 ° C. and a pressure of 10 Pa to 100 Pa. The result is shown in FIG.
[0033]
As shown in FIG. 5, it can be seen that the lower the pressure, the higher the carrier concentration. This is considered to be because the higher the pressure, the more the Zr occludes the atmospheric gas, and the lower the ability to occlude hydrogen. However, when heat treatment was performed at 10 Pa, measurement was not possible. This is because an ohmic electrode could not be formed due to deterioration of the surface state of GaN.
[0034]
As described above, the heat treatment conditions in which the heat treatment temperature is 700 ° C. and the degree of vacuum is 100 Pa as in Example 1 are consistent with the preferable heat treatment conditions derived from Examples 2 and 3.
[0035]
Also, from the results of Example 2, when the heat treatment temperature exceeded 700 ° C., sublimation and decomposition of GaN were observed. This is a result of performing the heat treatment in a vacuum, When heat treatment was performed under atmospheric pressure, sublimation and decomposition of GaN were not observed up to a heat treatment temperature of 800 ° C.
[0036]
In Examples 1 to 3, the heat treatment was performed in a vacuum. However, as described above, the heat treatment in a vacuum is more likely to cause decomposition and sublimation of GaN than the heat treatment under a pressure. In order to avoid the danger in this respect, it is considered that heat treatment under pressure is suitable, but it is necessary to consider the balance because the effect of the metal that occludes hydrogen may be impaired. .
[0037]
【The invention's effect】
In short, according to the present invention, a p-type gallium nitride-based compound semiconductor having a high carrier concentration can be formed from a gallium nitride-based compound semiconductor doped with a p-type impurity. This facilitates formation of a p-type gallium nitride-based ohmic contact, and enables a wide range of applications to devices including a p-type gallium nitride-based compound semiconductor.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of an annealing apparatus.
FIG. 2 is an explanatory diagram of an example of a sample stage.
FIG. 3 is an explanatory diagram of another example of the sample stage.
FIG. 4 is a diagram showing a relationship between a carrier concentration and a heat treatment temperature.
FIG. 5 is a diagram showing the dependence of carrier concentration on atmospheric pressure during heat treatment.
[Explanation of symbols]
1 Quartz tube 2 Sample transport rod inlet 3 Sample transport rod 4 Sample table 5 Sample heating heater 6 Exhaust port (to vacuum pump)
7 Sample stand (graphite etc.)
Reference Signs List 8 Groove for GaN-based compound semiconductor 9 Groove for hydrogen storage alloy 10 GaN-based compound semiconductor 11 Hydrogen storage alloy 12 Groove for sample

Claims (6)

Forming a gallium nitride-based compound semiconductor doped with a p-type impurity by a vapor phase growth method, and subjecting the obtained p-type impurity-doped gallium nitride-based compound semiconductor to a heat treatment together with a metal or an alloy capable of absorbing hydrogen; In the method for producing a p-type gallium nitride-based compound semiconductor, characterized in that, when the gallium nitride-based compound semiconductor doped with a p-type impurity is heat-treated together with a metal or an alloy capable of absorbing hydrogen, the p-type impurity is doped. A method for producing a p-type gallium nitride-based compound semiconductor, comprising arranging a gallium nitride-based compound semiconductor and a metal or an alloy having the ability to occlude hydrogen on the same sample stage and performing heat treatment. Forming a gallium nitride-based compound semiconductor doped with a p-type impurity by a vapor phase growth method, and subjecting the obtained p-type impurity-doped gallium nitride-based compound semiconductor to a heat treatment together with a metal or an alloy capable of absorbing hydrogen; In the method for producing a p-type gallium nitride-based compound semiconductor, characterized in that, when the gallium nitride-based compound semiconductor doped with a p-type impurity is heat-treated together with a metal or an alloy capable of absorbing hydrogen, the p-type impurity is doped. A method for producing a p-type gallium nitride-based compound semiconductor, comprising: bringing a surface of a gallium nitride-based compound semiconductor into contact with the metal or alloy having the ability to absorb hydrogen and performing heat treatment. 3. The method according to claim 1, wherein the metal or alloy having the ability to absorb hydrogen is zirconium or titanium. 4. 3. The method according to claim 1, wherein the heat treatment is performed in an atmosphere containing no hydrogen gas when the gallium nitride-based compound semiconductor doped with a p-type impurity is heat-treated together with a metal or an alloy capable of absorbing hydrogen. A method for producing a p-type gallium nitride-based compound semiconductor. 3. The method according to claim 1, wherein the heat treatment is performed in a vacuum when the gallium nitride-based compound semiconductor doped with the p-type impurity is heat-treated together with a metal or an alloy capable of absorbing hydrogen. A method for producing a p-type gallium nitride-based compound semiconductor. The method according to claim 1 or 2, when a heat treatment with the metal or alloy has the ability to absorb hydrogen-doped gallium nitride based compound semiconductor with p-type impurities, to carry out the heat treatment at 400 ° C. to 800 ° C. A method for producing a p-type impurity compound semiconductor, which is characterized in that:

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