JPH0637358B2 - Indium phosphide single crystal and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a single crystal of an indium phosphide compound semiconductor and a method for producing the same.

(Prior Art) It is well known that indium phosphide (InP), which is a III-V group compound semiconductor, serves as a substrate for various semiconductor devices, and in particular, a P-type InP substrate doped with zinc (Zn) has a high output. Used as a substrate for laser. For this type of semiconductor substrate, a single crystal having a low dislocation density, a high carrier concentration, and a high precision control is required in order to obtain an element having a desired quality.

The liquid-encapsulated Czochralski (LEC) method is generally used to produce Zn-doped InP single crystals. On the other hand, a single crystal substrate having a high carrier concentration is required for higher output as a laser device.

To obtain a high carrier concentration single crystal by the LEC method, use a material in which a carrier element is added at a high concentration in the raw material melt, increase the pressure in the pulling device as much as possible, and adjust the amount of sealant. Has been adopted.

However, depending on the conventional method, even if the carrier concentration in the raw material melt is increased to 10 ¹⁹ cm ^-3 or higher, the Zn concentration dependence of the effective segregation coefficient of Zn in InP, the vapor phase of Zn before the raw material is melted, 7 × 10 due to scattering into the inside and scattering from the solidified crystals into the gas phase
It is very difficult to obtain crystals having a high carrier concentration of ¹⁸ cm ^-3 or more. For example, Journal of Crystal Gro
wth P. As shown in 317, in the conventional method, the correlation of the carrier concentration with the Zn addition amount is described, and the maximum value of the carrier concentration is saturated at about 7 × 10 ¹⁸ cm ^-3 ,
Further addition of Zn has a drawback that the carrier concentration is lowered and the electrically inactive Zn concentration is increased. The purpose of the present invention is to set the initial Zn concentration in the melt in producing a Zn-doped indium phosphide single crystal by the LEC method,
A higher carrier concentration is obtained by controlling the cooling rate of the crystal after growth. It is to provide a method for producing a Zn-doped InP single crystal.

(Means for Solving Problems) InP single crystal of the present invention uses Zn as a dopant,
The carrier concentration was limited to 7 × 10 ¹⁸ to 2 × 10 ¹⁹ cm ^-3 .

Zn is used to obtain a P-type InP crystal with a low dislocation density. When a P-type InP crystal is used as a substrate, it has a large specific resistance and tends to make it difficult to form an ohmic contact, but the present invention facilitates the formation of a doped ohmic contact with a high Zn concentration.

As a result of increasing the doping amount of Zn, in the present invention, the carrier concentration
More than 7 × 10 ¹⁸ cm ^-1 . This is at a level not found in conventional crystals. Further, 5 × 10 ¹⁹ cm is the highest level obtained by the manufacturing method of the present invention. InP with carrier concentration in this range can be dislocation-free.

Next, in the method for producing an InP single crystal according to the present invention,
Taking advantage of the fact that the scattering of Zn from the crystal after solidification depends on its thermal history, a means for controlling the amount of Zn taken into the InP crystal, and thus the carrier concentration, is controlled by the cooling rate of the crystal. The proof that this method can be used is based on the inventor's finding that for the InP crystal obtained by the LEC method, the Zn concentration and the carrier concentration decrease before and after the heat treatment of the crystal after the pulling is completed. It is a thing. That is, the InP single crystal obtained by the LEC method was heated in a nitrogen atmosphere at 600 ° C × 5 Hr and cooled, and the ingot was measured for Zn concentration by the atomic absorption method and the
The carrier concentration was measured by measurement. as a result,
Before and after heat treatment, the Zn concentration decreased from 8 × 10 ¹⁸ cm ^-3 to 4 × 10 ¹⁸ cm ^-3 , and the carrier concentration decreased from 6 × 10 ¹⁸ cm ^-3 to 2 × 10 ¹⁸ cm ^-3.
It turned out to have fallen to. It was also clarified that the decrease in the carrier concentration becomes larger as the cooling rate of the ingot after heating becomes slower.

From this, by changing the amount of Zn added, the carrier concentration was set to 7 × 10 by setting the Zn concentration in the initial melt near the maximum value of the carrier concentration and increasing the cooling rate of the crystal after completion of crystal pulling. It is possible to increase the amount to ¹⁸ cm ⁻³ or more and reduce the amount of electrically inactive Zn.

That is, the Zn concentration in the melt shows that the carrier concentration in the pulled crystal shows the maximum value by adding Zn to the InP melt.
It is around 1 × 10 ¹⁹ cm ^-3 , and the maximum value of carrier concentration at this time is 7 × 10 ¹⁸ cm ^-3 . Therefore, it is necessary to prepare a raw material melt in which Zn is added to at least this maximum carrier concentration, and in the present invention, it is set to 8 × 10 ¹⁸ cm ⁻³ or more.

On the other hand, if Zn is added to the raw material melt more than necessary, not only the volatilization loss increases but also it becomes difficult to obtain a single crystal. Therefore, in the present invention, the upper limit of the Zn concentration in the raw material melt is 2 × 10 ²⁰ cm ^-3 .

The InP raw material melt thus prepared is pulled up according to the LEC method which is usually performed.

The feature of the present invention is that the cooling rate of the ingot after the pulling is completed is increased. In the LEC device, a thermocouple is usually inserted in the bottom of the crucible to control the crystal pulling temperature. The same thermocouple is used after pulling the crystal to control the cooling rate while adjusting the heater power. 50 to 150 ℃ / Hr for the purpose of reducing the thermal stress generated in crystals
The furnace was cooled to near room temperature at the rate of.

In the present invention, after the crystal pulling is completed, the temperature inside the furnace after the crystal is separated from the residual melt is controlled by a thermocouple at the bottom of the crucible, and the cooling rate is controlled to 150 ° C / Hr or higher. Achieving this cooling rate is achieved by further reducing the heater power than before. In the normal LEC equipment, when the furnace is cooled without supplying the heater current after pulling the crystal,
The cooling rate is about 1000 ℃ / hr. A crystal with a diameter of about 2 inches, which depends on the size of the crystal, will not be damaged even by such rapid cooling. Normally 150-900 ° C
/ Hr is suitable, and good results are obtained by cooling within this range and controlling to near room temperature.

Next, the present invention will be described with reference to examples.

Example of the Invention A quartz crucible having an inner diameter of 95 mmφ has a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ . 800g of InP polycrystal and Zn for dopant
It was filled with 156 mg and the pulling experiment was conducted twice in the single crystal pulling furnace. In addition to the above raw material weight, the amount of B ₂ O ₃ , the rate of temperature rise, and the pulling conditions were kept constant, and the cooling rate after cutting the crystal was changed.

After separating the crystals from the melt and B ₂ O ₃ , the temperature of the crucible bottom thermocouple was lowered to 80 ° C / Hr and 150 ° C / Hr, then the crystals were taken out, and the wafer cut from the same position was usually used as the Hall. Evaluation was performed by measurement. As a result, 150 ℃ /
The carrier concentration of crystals cooled with Hr was 1 × 10 ¹⁹ cm ⁻³ , whereas that of crystals cooled with 80 ° C./Hr was 6 × 10 ¹⁸ cm ⁻³ .

From this, it was possible to obtain crystals with a high carrier concentration by changing the cooling rate.

(Effects of the Invention) According to the present invention, it was difficult to obtain 5 × 10 ¹⁹ to 7 × 10 ¹⁸ cm.
-Zn-doped InP single crystal with carrier concentration of ^-3 or more
By adjusting the amount of addition of n and adjusting the cooling rate to a certain value or higher, stable results were obtained.

This method can control the carrier concentration in the crystal by changing the thermal history of the grown crystal even from the InP melt containing the same amount of Zn, and can change the carrier concentration in the crystal by ingot annealing. It suggests that.

Claims (2)

[Claims] 1. A zinc-doped indium phosphide single crystal having a carrier concentration of 7 × 10 ¹⁸ to 5 × 10 ¹⁹ cm ^-3 . 2. When producing a zinc-doped indium phosphide single crystal by the Czochralski method, the zinc concentration in the initial indium phosphide melt is set to 7 × 10 ¹⁸ × 1 × 10.
^A method for producing a high carrier concentration indium phosphide single crystal, wherein the cooling rate is set to ²⁰ cm ^-3 and the crystal is cut off after pulling the single crystal to 150 to 900 ° C / Hr.