JPH0610085B2 - Method for purifying indium solution using indium as solvent - Google Patents

Description

TECHNICAL FIELD The present invention relates to indium phosphide (InP), indium gallium arsenide (InGaAs), indium gallium arsenide phosphide (InGaAsP) and the like suitable as materials for semiconductor optical devices. TECHNICAL FIELD The present invention relates to a technique for purifying a liquid phase growth thin film of a III-V group compound semiconductor containing indium, and particularly to a group III and a group V using indium (hereinafter referred to as In) as a solvent for the purpose of use in liquid phase growth. The present invention relates to a method for purifying an In solution containing a combination of the above elements.

(Prior art) 0.9-1.6μ due to the long wavelength of optical transmission system
Attention has been focused on thin film single crystals of III-V group compound semiconductors containing In such as InP, InGaAs, and InGaAsP having a band gap in the m band. When the above III-V compound semiconductor thin film is used as the material for this optical element, it is necessary to reduce the carrier density of the thin film layer, and for that purpose oxygen, sulfur and other residual impurity metals in the crystal are reduced to reduce the crystal. Technology for high purification is important.

However, in the current technology, there is a limit to high purification by reducing oxygen, sulfur, and other residual impurity metals from an indium solution using In as a solvent (hereinafter referred to as “In solution”),
In the liquid phase epitaxial growth method using the In solution containing such impurities remaining, there is a limit to the purification of the growing thin film.

In addition, semi-insulating InP, InGaAsP, InGaAs with extremely high resistance
In-based thin films such as are important as element isolation thin films for electrically isolating the substrate material of elements or elements. To increase the resistance of these thin films, iron (Fe) or nickel (Ni) must be used.
It is known that the deep levels formed by these transition metals are utilized by adding such substances to the thin film.

However, the current technology has a limit to high purification by reducing oxygen, sulfur and other residual impurity metals from an In solution added with a transition metal such as Fe or Ni, and a liquid phase epitaxial growth method using this solution grows. There is a limit to increase the resistance of the crystal thin film.

Up to now, when a high-purity InP, InGaAs, InGaAsP, or other In-containing III-V compound semiconductor thin film (hereinafter referred to as “In-based thin film”) is grown by a liquid phase epitaxial method using a normal carbon boat, A very long heat treatment was required.

That is, to explain the outline of a conventional liquid phase epitaxial growth method using a carbon boat, first, a raw material for a solution for growing a thin film is placed in a carbon boat, and the raw material is placed in a vacuum or a high-purity hydrogen atmosphere at 640. ℃
Heat at a high temperature of ~ 850 ° C for 10 to several tens of hours.
This evaporates the impurities contained in the solution and improves the purity of the solution. After that, the solution was cooled to room temperature, and the substrate crystal was placed on a carbon boat, heated again, and the solution was sufficiently melted and then cooled. The substrate crystal was kept at an appropriate temperature lower than the saturation temperature of the solution for a certain period of time. By contacting with a solution, high purity InP, InGaAs, In
In-based thin films such as GaAsP are grown.

Further, in order to obtain a crystal thin film of higher purity, it was necessary to repeat the above-mentioned growth process several times. That is,
After the thin film having a certain thickness is grown by the above-described method, the substrate is once pulled out from the reaction furnace, the solution is heated again for several tens of hours, and then the substrate is brought into contact with the solution again to further grow the thin film.

As described above, conventionally, in order to grow the above-mentioned thin film of high purity, in order to evaporate impurities in the raw material and increase the purity, the raw material is heated at high temperature in a vacuum or in a high-purity hydrogen atmosphere.
There is a drawback that heat treatment for a long time is required and heat treatment for an extremely long time is required.

(Object of the Present Invention) An object of the present invention is to provide a method for purifying an In solution using In used as a solvent in a liquid phase epitaxial growth method in realizing high purification of an In-based thin film grown by the liquid phase epitaxial growth method. To do.

Another object of the present invention is to provide a method for purifying an In solution that requires a short processing time.

(Outline of the Present Invention) The present invention purifies an In solution containing In, InP, etc. and Co or In, InP, etc., Co, and a transition metal by heating to melt In. In the above heating and melting, a method of heating and melting In, InP, etc. and Co at the same time, and once heating and melting In and Co or In, Co and transition metal, adding InP, etc. and heating and melting again. There is a method.

Co added when the In solution is prepared by heating and melting
React with phosphorus (P) or arsenic (As) to form a very stable cobalt phosphorus compound (CoP, Co ₂ P, Co ₃ P) or cobalt arsenic compound (CoAs, Co ₂ As, Co ₃ As). When these compounds are formed, oxygen, ions, or residual impurity metals having a large partition coefficient such as silicon and zinc are incorporated into the compounds. As a result, a high-purity In solution can be obtained.

Further, there is an advantage that the processing time required for high purification is short.

(Examples of the present invention) The present invention will be described below based on examples.

Example 1 First, an example of the present invention will be described in detail by taking as an example a case where a high-purity InP thin film is grown on a semi-insulating InP substrate by a liquid phase epitaxial method using an ordinary slide boat.

First, 3.5 g of 99.9999% pure In, about 40 mg of 99.9999% pure Co, for example, 185 mg of an additive-free InP single crystal with a carrier concentration of 5 × 10 ¹⁵ cm ⁻³ were weighed (Co bound to P, P The amount of InP is larger than that when no additive is added in consideration of the decrease in the degree of saturation.), And put it in a tank of a carbon boat in a high-purity hydrogen atmosphere (flow rate 800 ^cc / min) at 850 ° C 3
Perform heat treatment for an hour. By this heat treatment, a cobalt phosphorus compound is formed in the In solution, and various residual impurities in the In solution are incorporated into the compound when the compound is formed, so that a high-purity In solution can be obtained. Then, this high-purity In solution is cooled to obtain a raw material for InP growth. After this, semi-insulating InP
After the substrate was set in a boat, it was kept in a high-purity hydrogen atmosphere at a saturation temperature of 720 ° C. for 1 hour, then slowly cooled at 0.6 ° C./min, and the raw material obtained above was melted again to prepare an InP growth solution. At 710 ° C., the InP thin film is grown by contacting the substrate to 690 ° C.

The InP thin film thus grown had a film thickness of about 7 μm, and its surface was kept in a mirror state. The lattice constant and the peak wavelength of the photolumi spectrum are consistent with the InP thin film grown without adding impurities.

In addition, as a result of Hall measurement of the grown InP thin film, the mobility at room temperature was about 4700 cm ² / VS carrier concentration 1 × 10 ¹⁶ cm ^-8 77 °
Mobility at K 22000 cm ² / VS carrier concentration 8 × 10 ¹⁵ cm ^-3
Met.

This value is compared to the mobility (room temperature ~ 4200cm ² / VS, 77 ° K ~ 16000cm ² / VS) of the InP thin film grown under the same growth conditions as other heat treatment conditions using an In solution without addition of Co. about 5000 cm ² / VS larger at about 500cm ² /V.S77°K at room temperature. This shows that the addition of Co to the In solution increased the degree of transfer, that is, the purity was increased.

The reason why such a high-purity InP thin film is obtained is that the high-purity In solution is used and that the cobalt phosphorus compound in the high-purity In solution is not incorporated into the thin film during crystal growth.

In this example, since the long-time heat treatment that was performed in the conventional technique is unnecessary, the In solution purification and the In
Epitaxial growth of thin films is possible.

FIG. 1 shows the electrical characteristics at 77 ° K when InP thin films were grown on a semi-insulating InP substrate, using a Co-added In solution and a non-added In solution, and growing them alternately and continuously under the above-mentioned conditions. Show.

The ∘ mark shows the case where the Co-added In solution was used, and the X mark shows the case where the InP was grown using the non-added In solution.

As is apparent from FIG. 1, the mobility of the InP thin film when grown using the Co-added In solution is increased, and a higher-purity InP film is obtained. It was also confirmed that the growth of the InP thin film by using the Co-added I solution did not affect the purity (mobility) of the InP thin film grown by using the undoped In solution later.

On the other hand, FIG. 2 shows the mobility of an InP thin film grown by varying the amount of Co added to the In solution and selecting the amount of InP so as to keep the growth temperature at 710 to 690 ° C. Even with the addition of a small amount of Co of about 2 mg, an InP thin film having a mobility of about 20,000 cm ² / VS at 77 ° K was obtained.

Further, even when growing an InGaAs or InGaAsP thin film, Co forms an extremely stable compound with As at high temperature, and therefore, the same effect as in InP can be obtained.

Example 2 Next, an example aiming at a higher purification of the crystal thin film than in Example 1 will be described.

This embodiment is characterized in that the purification process is divided into two stages, instead of purifying the In, Co and InP single crystals by heating and melting them all at once. That is, first, In and Co are heated and melted to perform the first purification, and then InP is added to this to heat and melt to perform the second purification.

Specifically, first, 3.5 g of 99.9999% pure In,
About 40 mg of Co having a purity of 99.999% is weighed, put in one tank of a carbon boat, and heat-treated at 850 ° C. for 24 hours in a hydrogen atmosphere containing 0.05 ppm of oxygen. The reason for adding a trace amount of oxygen to hydrogen in this heat treatment step is that if hydrogen treatment is performed at high temperature for a long time, silicon (Si) will be mixed into the solution from the quartz tube, and crystals will grow using this solution. In this case, since the n-type impurity concentration in the crystal thin film becomes high,
This is to prevent mixing of Si into the In solution. The oxygen added may be 0.01 to 0.2 ppm. Then, it is cooled to obtain a high-purity raw material in which Co is added to In. Further, 190 mg of high-purity (for example, carrier concentration 5 × 10 ¹⁵ cm ⁻³ ) InP single crystal was weighed, put in the same tank as the high-purity In and Co raw materials described above, and placed in pure hydrogen (gas flow rate 800 cc / min). Heat-treated at 720 ℃ for 20 hours to obtain high purity I
Obtain a solution. Then, this high-purity In solution is cooled to room temperature to obtain a high-purity raw material for InP growth. After this, semi-insulating I
The nP substrate was set in a boat, kept in a high-purity hydrogen atmosphere at a saturation temperature of 720 ° C. for 1 hour, then slowly cooled at 0.6 ° C./min, and the above-mentioned high-purity raw material was again heated and melted into an InP growth solution. The substrate is contacted at 710 ° C. and an InP thin film is grown to 690 ° C.

The InP thin film thus grown had a thickness of about 7 μm, and the surface of the thin film was kept in a mirror state. As a result of Hall measurement of the grown InP thin film, n-type mobility at room temperature was 4800 cm ² / V.
S, resistivity 2.3 Ωcm, carrier concentration 5.7 × 10 ¹⁴ cm ^-3 , 77 °
The mobility at K was 72,000 cm ² / VS, the resistivity was 0.15 Ωcm, and the carrier concentration was 5.3 × 10 ¹⁴ cm ^-3 .

For comparison, the amount of InP was 85 mg without adding Co, and the growth conditions including other heat treatments were the same.
The electrical characteristics of the InP thin film are that the mobility at room temperature is 4400 to 4100 cm ² /
VS, carrier concentration 5 to 2 × 10 ¹⁵ cm ^-3 Mobility at 77 ° K 3
8,000 to 30,000 cm ² / VS carrier concentration 4.5 to 1.5 × 10 ¹⁵ cm
^{-It is} about ^-3 .

FIG. 3 shows a change in mobility of the InP thin film at 77 ° K when alternately grown with a Co-added In solution and a non-added In solution under the same conditions as described in Example 2. (The mobility at 77 ° K indicates the substantial purity of the InP thin film. ◯ indicates the case where the Co-added In solution was used, and X indicates the case where the non-added In solution was used. In the case of using the added In solution, the mobility of the grown InP thin film is 30,000 to 40,000 cm ² / VS higher than that of the case of using the non-added In solution.
It can be seen that the InP thin film grown using the added In solution has extremely high purity.

In this example, since the purification is performed in two steps, a higher purity In solution can be obtained and a higher purity InP thin film can be formed.

Further, the ultra-high purity InP thin film can be formed without repeating the steps of heat treatment and thin film formation, which have been performed in the conventional technique, so that the process can be shortened.

Table 1 shows the carrier concentration at room temperature and the mobility at 77 ° K of the InP thin film grown using the same method as in Example 2 under various growth conditions.

Other growth conditions not described in Table 2 are the same as in Example 2.

Example 3 Next, an example of growth of a high resistance InP thin film to which iron is added will be described.

In order to increase the resistance of the InP-based thin film, it is necessary to reduce residual impurities in the solution as much as possible and add high-purity Fe. The Fe-doped InP thin film was grown by using Co addition to reduce the residual impurities as much as possible.

First, In3.5g with 99.9999% purity and Co40 with 99.999% purity.
mg, purity 99.999% Fe 40 mg are weighed, put into a tank of a carbon boat, and heated and melted at 850 ° C. for 24 hours in a hydrogen atmosphere containing 0.07 ppm of oxygen. Then the solution is cooled to room temperature. Next, high purity (for example, carrier concentration 5
× a 10 ¹⁵ InP of cm ^-3) and 150mg weighed to obtain a raw material for cooling InP grown to room temperature after heating for 20 hours at 720 ° C. in a high purity hydrogen atmosphere placed in the same bath. After setting the latter half insulating InP substrate in a boat, the substrate was placed in a high-purity hydrogen atmosphere.
Heat at 0 ° C for 1 hour, then cool slowly at 0.6 ° C / min.
The substrate is brought into contact with an InP thin film growth solution obtained by heating and melting the nP growth raw material again at 710 ° C. to grow the InP thin film up to 690 ° C.

The thickness of this InP thin film was about 7 μm and the surface was smooth. Moreover, this InP thin film has a very high resistance, and it is difficult to measure the normal hole. When the sheet resistance was measured using gold germanium nickel alloy as an electrode, the resistivity was
It was about 2 × 10 ⁵ Ωcm.

On the other hand, when an InP thin film was grown under the same conditions using an In solution containing only Fe without adding Co (see Example 1
Similarly, the amount of InP source is small when Co is not added. The resistivity of the InP thin film did not increase, and the resistivity was at most about several Ωcm, which was comparable to that of a normal undoped InP thin film.

As described above in Example 1, the high purity and high resistance InP thin film can be obtained. In addition to the fact that the InP thin film itself can be highly purified by the gettering effect of impurities by Co, Co is added. When a transition metal such as Fe or Ni is further added to the In solution, the amount of the transition metal added is much larger than the amount of residual impurities, and the distribution coefficient is relatively large compared to Co or the compound of Co. This is because Fe or Ni having a deep level is added to InP by heat treatment for a short time.

In this way, Co was added to the In solution at the same time as Fe to reduce the concentration of residual impurities, so that a high-resistance InP thin film could be easily obtained. Table 2 shows the electrical characteristics of the InP thin film grown in Example 3 with some growth conditions changed.

Example 4 Even if Ni was used instead of Fe in Example 3, In with high resistance
Can grow P.

Of the growth conditions of Example 3, oxygen was 0.05 ppm by heat treatment in an oxygen-added hydrogen atmosphere, the high-purity hydrogen atmosphere heat treatment condition was 720 ° C. for 24 hours, and the InP thin film growth start temperature was 6
It was carried out from 80 ° C. to a finish temperature of 660 ° C.

At this time, the Ni-doped InP thin film had a thickness of about 6 μm and had a smooth surface. When the sheet resistance of this InP thin film was measured using gold and zinc alloy electrodes, it was about 3700 Ωcm.

On the other hand, when an InP thin film was grown under the same conditions with the use of an In solution containing no Co and containing only Ni (however, when Co was not added as in Example 1, the saturation of the solution was The amount of InP source is reduced for adjustment.) The InP thin film does not have high resistance, and at most this heat treatment time is several Ωcm.
Met. Table 3 shows the growth conditions and the specific resistance of the Ni-doped InP thin film grown by partially changing the growth conditions of Example 4.

In this way, a high resistance InP film was easily obtained by adding Ni and Co to the In solution.

Here, the growth method of the high-purity InP thin film and the high-resistance InP thin film by the liquid phase epitaxial growth method has been described. The high-purity thin film using the getter action of the compound of Co and P,
Growing high resistance thin film. On the other hand, since Co forms a stable compound with As, this method is highly pure InGaAs and InGaAs.
P, InAs, InGaP or high resistance InGaAs or InGaAsP, In
It is obvious that it can also be applied to liquid phase growth of As and InGaP.

Furthermore, if the purity of the raw material is improved and the concentration of residual impurities in the raw material is reduced, the hydrogen treatment temperature can be lowered or the hydrogen treatment time can be shortened, and the amount of added metals such as Co, Fe and Ni can be reduced. Needless to say, can be highly purified and have high resistance.

The thin film crystal obtained by the present invention can be used for the production of thin film materials such as high-purity electronic devices such as avalanche photodiodes, PIN diodes, and FETs, element isolation layers of these electronic devices, and buried layers of semiconductor lasers.

Further, in Examples 1 to 4, various In solutions are once cooled, and the InP-based thin film is grown after being heated and melted again, but the InP-based thin film is continuously grown without once cooling the In solution. It goes without saying that you can do it.

(Effects of the Present Invention) As described above, the present invention uses In as a solvent and InP and In.
In the method of purifying an In solution containing GaAsP, InGaAs, etc., by adding Co to the In solution, Co and P
Alternatively, a compound of Co and As can be precipitated in an In solution, and residual impurities can be introduced into these compounds to reduce the residual impurities in the In solution.
There is an advantage that the solution can be easily obtained.

Moreover, there is an advantage that the time required for purifying the In solution described above can be shortened.

Further, as an application of the present invention, the substrate is brought into contact with the In solution purified by the purification method of the present invention to form I on the substrate.
If n-type thin film is grown, high purity InP, InGaAs
There is an advantage that a P, InGaAs thin film can be easily obtained.

Furthermore, since the residual impurity concentration in the In solution can be reduced by the purification method of the present invention, if this is applied to the liquid phase epitaxial growth method, high resistance InP, InGaAsP, InGa doped with a transition metal such as Fe or Ni can be applied.
As thin film can be easily obtained.

[Brief description of drawings]

FIG. 1 is a measured value of the mobility at 77 ° K with respect to the number of times of growth of an InP thin film alternately grown using a Co-added and non-added In solution of the present invention, and FIG. 2 uses a Co-added In solution. Of the InP thin film grown by heating at 77 ° K with respect to the Co addition amount, Fig. 3 shows 77 ° K with respect to the number of times of growth of the InP thin film alternately grown using the Co solution and the In solution not added.
It is the measured value of the mobility in.

Claims (3)

[Claims] 1. A method of purifying an indium solution using indium as a solvent, comprising indium and indium-containing III.
A method for purifying an indium solution, which comprises heating a Group V compound semiconductor material and at least cobalt to heat and purify the indium solution. 2. The heating and melting step is performed on the indium and the indium.
The method for purifying an indium solution according to claim 1, wherein the III-V compound semiconductor material and the cobalt are heated and melted together. 3. The heating and melting step includes two steps of once heating and melting the indium and the cobalt, then adding the III-V compound semiconductor material, and again heating and melting. The method for purifying an indium solution according to claim 1.