JPH01164800A - Semi-insulating gallium arsenide single crystal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to semi-insulating gallium arsenide single crystals.

[Prior Art] In recent years, as the development of gallium arsenide (GaAs) ICs progresses, the demand for high-quality semi-insulating GaAS is increasing.

Conventional methods for manufacturing high resistivity GaAS include
-, 1/1.96 = In the Niuni-pulling method or boat method shown in No. 1, chromium (Cr
) has been proposed.

Prior art (1) A method for manufacturing a thermally stable Or-dominated Cr-oxygen semi-insulating QaΔS crystal has been proposed, and the relationship between the oxygen concentration in the crystal and silicon (Si) degree has been investigated. many kinds)
I'm bored.

For example, regarding the oxygen concentration in crystals,
9911 and Special Public Service No. 59-29557 have an oxygen concentration of 4×
There is a description that when the thickness is 1016 cm3 or more, the crystal becomes semi-insulating.

-・For 5ili 1 degree in GaAS crystal, in Japanese Patent Publication No. 53-4-6070, 1015 cm '-3
There is a description that it will be made into a
10"cm'<S i <2X 10""cm-3
There is a description in Japanese Patent Publication No. 59-46918 that the concentration of at least one of tellurium and 3i is 5 x 1015 cm.
'Description of making it larger than ', Special Publication No. 59-29557
There is a statement that Si<2X1015 or less,
It is considered desirable to suppress the angle of 8181 degrees to 1×10″'cm-3 or less.

Prior Art (2) When a Cr- or Fe-doped semi-insulating crystal is manufactured using a boat made of quartz material, S1 contamination occurs, so it is necessary to add a large amount of deep acrylic impurities such as Cr or E.

As a method to prevent 3i contamination, △5203 or Ga
There is a method of doping oxygen in the form of 20, etc., and its effects are explained or cited as shown below.

Literature ■ C, N, Cochran et al:
J electrochem.

Soc 109 (1962) 149゜■ J, E, Woods and N, G 81nslie: J, Appl, Phys.

34 (1963) 1469゜■ J, H, 11oodall: Transacti
ons Met, Soc, AINF.

239 (1967) 378゜■ Matsuban (1!!: Sumitomo Electric, 97 (1968) 1
27■ Suzuki et al.: Proceedings of the 12th Semiconductor Specialized Seminar■
Akai: Kyoto Faculty of Humanities and Engineering Dissertation (1975) 3i contamination into GaAs is caused by the reaction of equation (1) with SiO2, which is the moon substance of the Qa boat in GaAs Mel 1~
c/1-.

(References ■～■ above).

4Ga(L)(in GaAs)+SiO(S)<-
3i (L) (in GaAs) → 2Ga 0 (G)
↑ ・ (1) (S, solid 1° liquid G,
On the other hand, it is said that the Ga2O gas generated in equation (1) undergoes a reaction in equation (2) within the reaction vessel, and the Ga2O gas is deposited in the form of Ga2O3 in the low temperature part of the reaction vessel.

3Ga 0(G)+^3Δ(G), ITI:Ga
O(S)+4Ga85(S)-'. (2) When the temperature of the low temperature part in the reaction vessel, that is, the diffusion barrier part is low,
It is said that as the precipitation of Ga2O3 is promoted, Ga2O gas is consumed, so the reaction in equation (1) moves to the right and contamination of 3i increases. , theories have been constructed based on the measurement results.

The mainstream way of thinking until now is Wooda l l
This is the idea of reducing 3i by adding AS203 in (the above-mentioned document ■), and it is introduced from the following equations (3) to (8) (9
), when the resistance of the diffusion barrier to Ga2O gas (-1) and the crystal growth rate (V) are constant, the 81 concentration in the GaAS crystal increases as the assimilation of the crystal progresses. This is an expression that shows that However, as will be shown later, our experimental results cannot be explained using this formula.

First, we will explain the symbols and then show the calculation process.

P: Ga2O gas pressure, D: Ga at S vapor pressure 1 atm F
Diffusion coefficient of 2O gas, Po: Initial Ga2O gas pressure, P
: Gas pressure of Ga2o at 1100°C J, V:
Crystal growth rate, X: length of crystal in longitudinal direction, t: time,
A: Diffusion barrier gap area 1, O: Diffusion barrier gap length, ■: Free space volume on the high temperature side of the quartz ampoule.

The calculation formula for introducing formula (7) is shown below.

From Fick's first law, the initial partial pressure [ ]. Assuming that the gas pressure becomes t at the opening time [ ], then we integrate equation (3) to obtain equation (4).

When the time t is close to O, it is possible that P > Pl, so the following equation (5) is obtained.

On the other hand, from equation (1), C (5iilfti degree in GaAs) = K (T)
/P2... (6) (Here: equilibrium constant) Substitute equation (5) into equation (6) to obtain equation (7).

Also, K/Po' = Go.(8) (Here, C8 is the initial concentration of Si in GaAs) Substituting equation (8) into equation (7), equation (9) is obtained.

This shows that when V, V, ρ/A, and D are constant, the Si concentration increases as X increases, that is, the solidification of the crystal progresses.

In the experiment of Woods (Reference ■), a high-resistance oxygen-doped GaAS was obtained on the seed side of the crystal, and Woodal
In the experiments of I (Reference ■) and Motoben (Reference ■), results were obtained in which the carrier concentration is higher toward the rear end of the crystal. However, this is not a direct measurement of the Si content in the crystal.

In our experiment, as shown in the later examples, Si1 degree decreased as the crystal solidification progressed, so we believe that the fact of our experiment cannot be explained solely by equation (9).

Based on the above considerations, our experimental results can be said to indicate that there is a possibility that the introduction of new ideas, not just conventional ones, may be explained as J:.

Prior Art 3 There is a problem in that oxygen doping causes wetting at the rear end of the GaAs crystal. Motoben (Reference ■) states that as long as the condensation reaction of Ga2O vapor is suppressed, severe wetting is unlikely to occur, and when the boarding reaction becomes active, wetting is promoted, and the condensation reaction does not occur. We developed a three-temperature LIB method that increases the temperature of the diffusion barrier.

However, this idea has some unclear points as shown below.

That is, in the above equation (1), 4Ga(1,)+SiO(s)4Si(1-)(in
GaAs)+2Ga 0(G) ↑・・・ (1
) When the condensation reaction is suppressed, the Ga2O gas pressure is high, so the parallelism of equation (1) holds, the α-cristobalite inside the quartz boat does not decrease, and no wetting occurs between the GaAs crystal and the boat.

As the progress of the condensation reaction becomes more active, the Ga2O gas decreases, so there is a possibility that equation (1) moves to the right and S i 11 degrees increases. Therefore, it can be said that the SI concentration is likely to be higher at the rear end of the crystal where wetting occurs.

However, direct measurement of Sl has not been performed. In our experiments, we observed a phenomenon in which the Si1 degree at the rear end of the crystal was low and wetting occurred.

Conventional technology (4) If a PUN boat is used, there will be no 3i contamination-Q
, - Although it was thought to be a thing, there was actually 1]B in the quartz ampoule.
When a GaΔS single crystal was produced by placing an N boat,
3i contamination was observed, and a conductive n-type crystal was obtained.

[Problems with the Prior Art] In Japanese Patent Publication No. 53-46070, etc., it is stated that all oxygen in the crystal functions as a deep donor impurity. It is not clear whether it exists in the crystal as a single substance, a compound, or an ion, and furthermore, it is possible to measure the concentration of oxygen in the crystal.
Considering that there was no means to do this, it cannot be said with certainty that all of the oxygen was ionized. Furthermore, As
It is reported that the oxygen concentration in a chromium-doped semi-insulating GaAs single crystal produced by the boat method with addition of 2O3 was 2.0 to 7.2 x 1015 cm-3 as measured by activation analysis.
on in a horizontal Br
idgmann-grown semi-insula
tion GaAs ingot: 5 hikano
.

et at, 8pD1. DhyS,1-ett,,4
6 (1985) 391-393), oxygen alone is insufficient to function as a deep donor in a single GaAStiII product;
It is thought that there are other things that can function as deep donors. In recent years, FL has been recognized as a deep donor.
2 is discovered - (and its 1li1 degree is usually 1 ”-
2X 1016 cm-3.

Therefore, considering the fact that it is unknown whether all of the oxygen is ionized, most of what functions as a deep toner in the Cr-doped GaAS single crystal is 1=12
J is like this.

Furthermore, when considering conventional techniques (2) and (3), wetting occurs in the crystal when an Or-oxygen semi-insulating crystal is grown using a 5102 boat, but the wetting mechanism is clearly 41 Not yet. According to the conventional thinking, the degree of 5illfa increases as the crystal v1 ends.

However, in our experiments, the 3i degree at the rear end of the crystal is low and wetting occurs. In this way, conventional theories cannot explain our experimental results.

Furthermore, when considering conventional technology (4), stone =
11 - Grow a GaAs crystal in PBN bow 1 using a quartz ampoule.
It is thought that SiO gas is generated by the =J@L reaction, and that this SiO is dissolved in the GaAS in the P 13N boat, causing S1 contamination.

(It is also possible that the oxygen component of SiO2 is incorporated into the crystal). Therefore, even when a P 13 N boat is used, the semi-insulating crystal can be made 1q by simultaneously adding Or while reducing 3i by adding oxygen.

OBJECTS OF THE INVENTION One object of the present invention is to provide a semi-insulating Ga AS single crystal that is hardly affected by the oxygen concentration in the crystal and has excellent thermal stability.

The gist of the present invention is that most of the deep tonneau level formed is at L2, and the total concentration of donor impurities (including Lime) is greater than the total concentration of donor impurities including Fl-2; Semi-insulating Ga where the shallow acceptor impurity concentration is small sum J of donor impurity levels including Fl-2
The reason is that it is made of AS single crystal.

[Supplementary Explanation] Explanation of the Present Invention by Energie Bird FIGS. 1(a) and 1(b) show the electronic state of semi-insulating gallium arsenide according to the present invention.

In FIGS. 1(a) and (b), "SD is i11 degrees of the shallow donor impurity level, NSA is the concentration of the shallow acceptor impurity level, NDO is the concentration of the deep donor impurity level, and NEL2 is the concentration of the impurity level. Concentration of FL2 level without, ND
A represents the concentration of a deep acceptor impurity level, [f] represents the lumi level, 1 represents the conduction band, and 2 represents the valence band. N,
. is considered to be the level of oxygen impurity, and the level of NBp, @rim impurity.

Semi-insulating crystals need to be thermally stable.

That is, the process of shrimp growth, etc.] is heated during the second stage.

The conditions for maintaining high resistance even after heat treatment are that the Fermi level (]3f) is at the level of N, N, EL2 DD D
It is thought that it is located in the vicinity of .

FIG. 1(a) shows an electronic state in which an Or-dominated crystal maintains high resistance. The condition for high resistance is that the Fermi level ET is near NDD, and the following equation holds true.

N DA> N SD-N SA> O〈 ” NS
A ten N DA〉 NSO2N5A) ... (
10) Furthermore, FIG. 1(b) shows the electronic state in which the FL2-dominated crystal maintains high resistance.

The condition for high resistance is that the full level is near NDD, and the following equation holds true.

NDD-I-N[L2>NSA-NSD>ON [L2
- “DD”-N SA” N DD”-N E
L2 − N SD > N SA) (10) When the equations (10) and (11) are aligned, a thermally stable semi-insulating crystal is obtained.

[Examples] Example 1 A Cr-doped crystal was grown using a quartz boat using the G method (gradient freezing method).

2 using 6N (purity 99.9999%) Ga and AS
500 g of GaAS single crystal was grown.

At this time, 30 mq of AS203 was installed outside the boat. 5N (purity 99.999%) Cr is 5N (purity 99.999%)
60 ppma (to 2500 g of GaAs) was added.

The obtained GaAs single crystal has a dislocation density of approximately 6000 c
m” or less.

Analysis of Cr and 3i in this crystal was performed using a G1]-discharge mass spectrometer (GDMS). Oxygen analysis was performed by activation analysis.

Figure 2 shows the Si concentration in the crystal (GDMS measured values Cr and Sl
It is said that the ionic strength ratio is equal to the atomic temperature (ppma)) and the oxygen concentration (
Literature: Shibata et al., Proceedings of the 22nd Tokyo Symposium on Applied Spectrometry (1987) 61).

3i concentration is 0 at seed part, solidification rate Q=0.1, 4II1
1ma (1, -17x 1.016cm-3>, dill part solidification rate q = 0.8 O, (0,89x 1015c
m-3>. Cr1 degree has solidification rate: 0 at G=0.1
, 5pl) ma (2,2X 1016ctn-”),
o=-o, 2.7 ppma at 8 (1, 2X 101
7 cm'-'').

For shallow acceptor impurities, the sum of Ca etc. is 0.02
1) Dma (1,8X1015 cm-3), I'A element was 1X10 cm X [L2 was 1x10 cm.

The oxygen concentration is approximately 1.5X 1 at the seed solidification rate q-0.1
0"' cm-3 tail part a=0.8, approximately 1 x 1016
cm'.

When the specific resistance of this crystal was measured by the van der Para method, it was found to be approximately 5×10 7 Ωcm or more.

Furthermore, it was found that even when heat treatment was carried out at 800 DEG C. and 30 ml in a 1-12 air flow, the specific resistance was approximately 5.times.10@7 .OMEGA.cm or more. It was found that oxygen in this crystal increased as the crystal grew, and that it segregated according to the normal freezing equation shown in Figure 2.

C(Q)-C0Keff (1-(J)""f-10°Ci initial oxygen concentration), Keff: (effective segregation coefficient),
g: (Solidification rate), C (g) The oxygen concentration K e f f at the end of the solidification rate q was obtained as a value of about 0.35 to 0.4, so the oxygen concentration in the crystal changes due to segregation and C It turned out that there was.

There are many unknown points regarding the behavior of oxygen and Si in crystals.

Si by adding oxides such as As2O3 or Ga2O3
There is no doubt that the suppression of contamination depends on the Ga2O gas partial pressure as shown in the prior art (3). However, in this way of thinking, as shown in the prior art, as the crystal solidifies, the temperature of the diffusion barrier decreases and the GaO gas becomes Ga2.
It is thought that Si is precipitated in the form of O3, which reduces the partial pressure and increases the Si concentration.

However, in the crystal of the present invention, as the crystal solidifies, 5iif1
It can be seen that the crystallinity is lower and different from conventional crystals.

Considering Si contamination, the relationship between 81 and oxygen in the GaAs melt can basically be explained by the following equation (14): S + 02 (quartz boat>->s: (i
nQaΔ5)4-20(inGaAs>・(141
The melting point (123
The equilibrium constant near 8°C can be expressed as follows:

s+ O5i02μ3i, oxygen, 3i where a ・
, a , a O? The respective activities of a, 1o2-1°Si concentration and oxygen concentration are extremely small, so if the activity coefficient is 1, then (1
Equation 5) can be expressed as equation (16).

ni = Ns, -No ・ (16
) Taking the logarithm of equation (16) gives equation (17).10 (INo and IQ(I
When we look for the relationship between Nsi, the slope is - 1dandariG
It was found that the product of temperature and S1 temperature is constant in the aA crystal.

In other words, if appropriate Ifi oxygen is present at the initial stage of crystal growth, a crystal with good thermal stability with a lower 3i degree than that at the beginning of crystal solidification will be obtained. Judging from the low concentration, this seems to be due to IE L2.

Example 2 A Cr-doped crystal was grown using a quartz boat coated with BN by the GF method.

A 2500Q GaAs single crystal was grown using 6N Ga and As. At this time, AS203 was installed outside the 30mQ port. 5N Cr is 560 ppm in the port
a (for GaΔ525,000) was added. 1F gallium arsenide single crystal has a dislocation density of approximately 8000 cm
-3 or less.

The Si degree in this crystal is 1,5 x 1016 cm-
It was 3 or less.

The Cr concentration is 0 = = 0.1, 51) I) ma (
2, 2X 1016cm-3) g=o, 2 at 8,
It was 7 ppma (1,2X 1017 cm-3).

The total sum of shallow acceptor impurities is 1.5×15' −
310cm, EL21.2X1016cm-3.

The oxygen concentration was below I x 1016 cm-3. 1
However, when the specific resistance was measured, it was found that it was a semi-insulating crystal with a resistivity of approximately 5×10 7 Ωcm or more.

Furthermore, it was found that even if heat treatment was performed at 800° C. for 30 minutes in a H2 stream, the specific resistance was approximately 5×10 7 Ωcm.

From the above results, even if a 13N-treated quartz boat was used, oxygen in the atmosphere suppressed the generation of 3i, so that a crystal with a low 3i concentration, high resistivity, and good thermal stability was obtained. This thermal stability is thought to be due to [1-2], considering the low oxygen concentration in the crystal.

"Effect of the invention" According to the present invention, the following remarkable effects are achieved.

(1) According to the present invention, the following remarkable effects are achieved. Unlike conventional chromium, oxygen, and doped GaAs-1 crystals, it has excellent thermal stability without being affected by oxygen concentration.

(2) Conventionally, it has been said that Si contamination in GaAS crystals mainly occurs due to the reaction between quartz boats and Qa, and 3i reduction has been carried out by adding Δ5203. However, it was confirmed that Sl contamination was observed in the crystals grown using the BN-coated quartz boat, and the crystals became conductive. Using a BN coating boat, we were able to develop a semi-insulating crystal doped with Or.

(3) The Cr-doped crystal described in the previous item (2) has an advantage in terms of high quality, such as extremely low Si 1 degree, no precipitation of 3i, and high in-plane resistivity.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram (not showing the electronic state) of the semi-insulating gallium arsenide of the present invention, where NSO is the concentration of a shallow deboe impurity unit, NSA is the concentration of a shallow acceptor impurity level, and NDD is a deep 1 Li-1 impurity level. NFL2 is the concentration of the L:L2 level that is not an impurity, NDA is the concentration of the deep acceptor impurity level, E f is the F[lumi level, 1 is the conductor,
2&: indicates a single valence band. Figure 2 is an explanatory diagram showing the relationship between Si1 degree and O concentration in the crystal of the present invention, 3 is the Si concentration curve, 4 is the 1st (α) Cr bearing surface -e-+ N5D (b ) acid tree woman hairstyle-()-Ns[)

Claims (1)

[Claims] (1) Specific electrical resistance at 300°K is 10^6Ω・c
In a semi-insulating gallium arsenide single crystal with a diameter of m or more, at least chromium is included as an electrically active substance forming a deep acceptor level, EL_2 is included as an electrically active substance forming a deep donor level, and a shallow Regardless of the magnitude relationship between the sum of the concentrations of electrically active impurities and lattice defects that form the donor level and the sum of the concentrations of electrically active impurities and lattice defects that form the shallow acceptor level. First, the relational expression N_D_A>N_S_D-N_S_A>-N_E_1_
The concentration of impurities, the concentration of lattice defects, and E
A semi-insulating gallium single crystal characterized by containing a concentration of L_2. However, N_D_A is the deep acceptor concentration, N_S_D
is the shallow donor concentration, N_S_A is the shallow acceptor concentration, and N_E_L_2 is the concentration of electrically active EL_2 that forms the deep donor level.