JPS5946918B2 - Semi-insulating gallium arsenide single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a stable semi-insulating material that has a high specific resistance at the end of growth and can maintain a high electrical specific resistance even after being subjected to process treatments in the usage environment such as heat treatment and epitaxial growth. This invention relates to a single crystal of a V-group compound.

Semi-insulating ■-V group compound single crystals, such as semi-insulating gallium arsenide, are used in various planar devices such as field effect transistors (FETs), microwave devices such as Gunn diodes, optical semiconductor devices such as optical integrated circuits, and even Hall elements. Recently, its application as a substrate for type elements has been rapidly expanding. The various devices mentioned above are manufactured by processes such as epitaxial growth and ion implantation, but problems such as abnormal phenomena that occur at the interface between the semi-insulating gallium arsenide substrate and the active layer during the process, and changes in the resistance of the substrate to lower it. Currently, this is a major obstacle to improving device manufacturing yield. In the present invention, by controlling the doping conditions of various impurities so as to compensate for electrically active defects that occur during processing of the substrate, semi-insulating gallium arsenide monomer is made which is stable against processing. It provides crystals and greatly contributes to improving the yield of device manufacturing. Conventional, semi-insulating ■
- Group V compound single crystals include indium phosphide doped with chromium or iron, gallium phosphide doped with chromium, gallium arsenide doped with chromium, iron or oxygen, and also the "semi-insulating "Gallium arsenide crystal" (Patent application dated April 4, 1972, 1972-33)
As described in JP-A-48-102570), there is a composite semi-insulating gallium arsenide doped with at least one of chromium and iron as a deep acceptor and oxygen as a deep donor. The present invention provides a novel semi-insulating gallium arsenide single crystal that has the same basic structure as this composite semi-insulating gallium arsenide and has thermal stability particularly suitable for practical processing. be. Hereinafter, the present invention will be explained using the drawings.

1 to 4 are energy band diagrams for explaining the basic principle of the present invention.

In the figure, 1(NO) is a shallow donor impurity concentration, 2(NO) is a shallow donor impurity concentration,
NA) is shallow acceptor impurity concentration, 3 (NAA) is deep acceptor impurity concentration, 4 (NOO) is deep donor impurity concentration, 5 (Ef) is Fermi level, 6 (Nl)
indicates a relatively shallow acceptor concentration, 7 indicates a conduction band, and 8 indicates a valence band. FIGS. 1 and 2 are energy band diagrams of a single crystal of a semi-insulating -group compound containing either an acceptor or a donor as a deep impurity,
Figures 3 and 4A are energy band diagrams of a single crystal of a composite semi-insulating -group compound, and Figure 3 shows the case where the deep donor level is closer to the valence band than the deep acceptor level. , Figure 4A shows the case where the positions of the energy levels are reversed, but in both cases, the NA between the impurity concentrations
Satisfying the relational expression A>ND-NA>-NOO,
This is a necessary and sufficient condition for becoming semi-insulating. Next, consider the case where a semi-insulating single crystal is subjected to processes such as epitaxial growth and annealing. NAA>N
Taking the case of a composite semi-insulating V group single crystal called O-NA〉-NDO as an example, and explaining it using Figure 4, a shallow acceptor is generated during the process, and if its concentration is N~, then , in order to maintain semi-insulating property, NAA>ND-(
The following relational expression must be satisfied: NA+NA')>-NOO. If the single crystal satisfies NAA>NO-NA, the left side of the above relational expression is naturally satisfied. Regarding the right side, even if NO-NA>-NOO is satisfied before processing, it does not necessarily satisfy ND-NA>-NOO+NA' after processing. If this inequality cannot be satisfied, it is clear that the Fermi level approaches the valence band, transforms into P type, and cannot maintain semi-insulating properties. In order to compensate for NA′ newly generated by the process treatment and maintain the Fermi level near the center of the forbidden band,
N for the relationship NOlNAsNOO. -NA〉-NOD+N
It is a necessary and sufficient condition that impurities are included so as to satisfy A. It compensates for electrically active donors and acceptors generated during the device manufacturing process, and can maintain semi-insulating properties after the process as well as before the process. It is an object of the present invention to provide a truly stable semi-insulating gallium arsenide single crystal, with at least 50% of the surface of the gallium arsenide single crystal.
Inside 0 Å or more, the relational expression NAA-ND'〉ND-NA
〉-NDD+NA' is doped with impurities. However, NO' is the concentration of shallow donors generated during processing. Let us consider the concentration of electrically active acceptors and donors newly generated through processing, using gallium arsenide as an example. 700 for semi-insulating gallium arsenide in hydrogen gas. When heat treated at a high temperature of ~900°C, the surface has 1016 to 1018 vacancies of arsenic and gallium in order to maintain thermodynamic equilibrium. -3 is generated and diffused into the substrate. Each of these vacancies is thought to act as an electrically active shallow donor-acceptor. These shallow donor and acceptor diffusion depths were calculated using the Journal of Applied Physics.
Of Applied Physics) Volume 46.2986
Calculation using the diffusion coefficient described on page 2991 (1975) shows that, for example, heat treatment at 800°C for 2 hours
The result will be as shown in the figure. As is clear from this figure, the semi-insulating gallium arsenide has a thickness of 500 mm (0.05 μm) from the surface.
) The concentration of arsenic vacancies (A) is abnormally high in the surface layer,
It can also be seen that even if S is located inside, it is affected by relatively shallow donor acceptors of 1014CfL-3 or more up to a depth of several μm from the surface.

Regarding surface alteration, the above process is adopted, although it is thin enough to be removed by, for example, a gas etching process before the start of vapor phase epitaxial growth, a melt back process before the start of liquid phase epitaxial growth, etc. If not, or depending on the environment during high-temperature epitaxial growth, there is a good possibility that a degraded layer will be introduced, causing deterioration of device characteristics. In gallium arsenide, arsenic vacancies and gallium vacancies generated during the process are also compensated for by complexes of these vacancies and other impurities, so electrically active NA
', NO' is at most 2X1017c1n-3. The semi-insulating gallium arsenide single crystal according to claim 2 has a concentration of electrically active acceptors and donors produced by a process that is estimated to be the maximum and that is considered to be effective in practice. It describes the impurity addition and addition conditions for stable semi-insulating gallium arsenide when estimated as follows. The present invention will be explained below with reference to Examples.

Example 1 FIG. 6 is a block diagram of a three-temperature type crystal growth furnace used in the production of gallium arsenide single crystals in this example, a temperature distribution diagram in the furnace, and a diagram of a crystal growth container.

The manufacturing method is as shown in the figure, the temperature of the crystal growth furnace is approximately 1245℃.
~1270°C (T1) high temperature heating section 17 and 1080°C
The quartz boat is equipped with an intermediate temperature heating section 18 that heats the temperature to ~1,2000C (T2) and a low temperature heating section 19 that heats the arsenic to a level where the vapor pressure becomes approximately 1 atm (T3), and serves as a boat for storing gallium arsenide. 15, using a quartz boat 15
As the sealed container 9 for accommodating the boat 15, a chamber for accommodating the boat 15, a chamber for accommodating the arsenic 13, and a pore section 14 provided between these chambers for inhibiting the flow of arsenic vapor is used. The distance (L2) between the boundary line of the pore section 14 with the arsenic storage chamber and the lowest temperature position of the intermediate heating section 18 is
The length is approximately equal to or longer than the total length (L1) of the quartz boat 15, and gallium 550 is contained in the quartz boat 15.
f1 (purity 99.9999%) chromium 5g, tellurium 6~
and AS2O33O, and arsenic 6609 (purity 999999%) was housed in the low temperature part of the sealed container 9, and a gallium arsenide single crystal was grown at a crystal growth rate of about 2 to 1011/hour. In FIG. 6, 10 is a gallium arsenide melt, 11 is crystallized gallium arsenide, 12 is a gallium arsenide seed crystal, 16 is a furnace core tube, and 20 is a temperature distribution curve. The electrical resistivity of the obtained crystal was measured by the van der Pauw method, and the resistivity at 3000 K was approximately 2 x 10 8 Ω・α, and the surface leakage current was measured by the stylus method. As a result, it was less than 1 μA for an applied voltage of 1,000 volts over the entire surface of the measured wafer. Mass spectrometry analysis of this crystal revealed that silicon was approximately 1X
1015 cm-3, tellurium is approximately 1 x 1016 cm-3, chromium is approximately 1.5 x 1017 cTn-3, oxygen is approximately 8 x 1
It was found that 016crn-3 was included. After heat-treating this crystal at 800°C in hydrogen gas for about 2 hours,
Step etching was performed using a sulfuric acid/hydrogen peroxide based etching solution in 0.5 μm increments from the surface, and the leakage current was measured using the stylus method. It was found that it is semi-insulating. In addition, the impurity concentration of the crystal obtained in this example and the inequality NAA-NO'>ND-NA>-NDD-
The correspondence with NA5 is as follows. NAA (Chrome)+
1.5×1017c! n-3N0 (silicon + tellurium)
+1×1015+1×1016=1.1×1016cm
-3N+0 A N0D (oxygen)+8×1016cTn-3, so
Substituting into the above formula, 1.5×1017-NO'〉1.1Kari016〉NA'-
8×1016, but the heat treatment conditions are 80×1016 in hydrogen gas.
Since it is 0℃ for about 2 hours, it is N from Figure 5.

'≦(VAS-VGa)MaXl. 37×1017CT
Since n-3, NA' is 9×10 16 α-3, it is clear that the above formula is satisfied. Example 2 When producing a gallium arsenide single crystal by the three-temperature horizontal Bridgeman method in the same manner as in Example 1, 500% of chromium was added.
The other conditions were the same as in Example 1.

This crystal has a chromium concentration of approximately 1.5X10i6c7rL
The results were the same as in Example 1 except that the value was -3. In addition, this crystal had a leakage current of less than 1 μA when 1,000 volts was applied before heat treatment, but when 800 volts was applied in hydrogen gas,
By heat treatment at ℃ for 2 hours, about 200 layers of surface layer become n
It was found that the conductive layer of the mold had changed in quality. However, it maintained semi-insulating properties inside. In addition, in this example, the change in the surface layer of about 200 was due to NAA (chromium) +1.5 x 1016 cm-3, so NAA-
This is due to a partial collapse of the inequality NAA-ND''>ND-NA on the left side of NO'〉ND-NA〉-NDD+NA'. Verification example 1 As in Example 1, the three-temperature zone horizontal Bridgeman method was used. When producing a gallium arsenide single crystal, a gallium arsenide single crystal was grown under the same conditions as in Example 1 except that 19 chromium and 5η of AS2O3 were contained.

This crystal contains about 3 x 1016 cT of chromium, about 6 x 1015 cT'3 of silicon, and about 1.5 x 1016 cT of oxygen.
It was found that it contained n-3. Before heat treatment, this crystal has an electrical resistivity of approximately 2×10 8 Ω・? The leakage current measured by the stylus method was also less than 1 μA at 1,000 volts. However, when the same heat treatment as in Example 1 was carried out, the number of surface layers 100λ was equal to the force showing semi-insulating property\number 1
Although the resistance is relatively high from 00 λ to several 1,000 A, it has been found that it changes to P-type conductivity, and that it maintains insulating properties again at deeper depths. That is, in this verification example, the oxygen concentration was lower than in Examples 1 and 2, and the shallow acceptors generated during heat treatment could not be fully compensated for.
Inequality N on the right side of NA'. -NA〉-NOO (oxygen)+
It is thought that a region where NA is not satisfied is created. Verification example 2 When the single crystal grown in Example 2 was heat-treated in a gas containing hydrogen gas mixed with AsH3 gas at a volume ratio of approximately 1/10, the surface layer did not change to n-type. It did not occur.

From this, it was found that the surface n alteration was mainly caused by arsenic vacancies As. The present invention has been described above with reference to Examples, but the method for producing gallium arsenide single crystals is not limited to the three-temperature horizontal Blitzman method, but also the pulling method, etc.
Needless to say, it can also be obtained using a gradient freeze method or the like.

Even if a semi-insulating gallium arsenide single crystal that satisfies the constituent requirements of the present invention is used, an altered layer with low specific resistance may be formed from the surface up to about 500 mm when subjected to heat treatment or other processes at about 800°C. However, in general, high-temperature epitaxial growth involves a step of removing several micrometers of the surface layer of the substrate by vapor phase etching or meltback, so the active layer of the device is not affected. In addition, since an ion implantation layer of about 0.1 to 0.5 μm is uniformly formed in Hall elements, etc., the resistance including the surface layer of 500 A or less must be kept low, so such semi-insulating It can also be used with other substrates. As described above, the present invention
By configuring as described in the claims, a stable semi-insulating gallium arsenide single crystal that can maintain semi-insulating properties even under severe usage environments such as heat treatment and high-temperature epitaxial growth is provided. This greatly contributes to improving the yield and reliability of microphone mouth wave devices and optical semiconductor devices.

[Brief explanation of drawings]

Figures 1 to 4 are energy band diagrams for explaining the basic principle of the present invention. Figure 1 is a deep acceptor type, Figure 2 is a deep donor type, and Figures 3 and 4 are energy band diagrams. Figure 4 is an energy band diagram of a composite semi-insulating single crystal that was previously invented by the applicant. It is a band diagram.

Claims (1)

[Scope of Claims] 1. A semi-insulating gallium arsenide single crystal containing at least one kind of deep acceptor impurity and at least one kind of deep donor impurity and having an electrical resistivity of 10^6 Ωcm or more at 300°K, At least 500% from the surface of the single crystal when the crystal is processed in a suitable use environment.
Within Å or more, the relational expression N_A_A−N_D_′>N_
A semi-insulating gallium arsenide single crystal containing impurities so as to satisfy D-N_A>-N_D_D+N_A_'. However, N_A_A is the sum of deep acceptor concentrations, N_
D_D is the sum of deep donor concentrations, N_D is the sum of shallow donor concentrations, N_A is the sum of shallow acceptor concentrations, and N_D_' and N_A_' are the vacancies of arsenic atoms generated when the above single crystal is processed, respectively. It is the sum of a relatively shallow donor concentration containing pores and a relatively shallow acceptor concentration containing vacancies of gallium atoms. 2 N_D is a concentration of at least one of tellurium and silicon, and 5×
At least one type of acceptor impurity that is larger than 10^1^5 cm^-^3 and deep is chromium, and the chromium concentration is larger than the above N_D and is 1.2 x 10^1^6 cm^-
The semi-insulating gallium arsenide single crystal according to claim 1, which is smaller than ^3.