JPH0637360B2 - Method for growing ZnSe single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for growing a ZnSe single crystal, and more particularly to a method for growing a ZnSe single crystal, which is highly expected as a blue light emitting material. Is related to high quality.

(Prior Art) A ZnSe single crystal is usually manufactured by a high-pressure Bridgman method. The high-pressure Bridgman method has an advantage that a large circular single crystal can be easily grown. However, the single crystal produced by the conventional method has a drawback that high-density crystal defects, especially dislocations and twins are present. The reason for this is that the above crystal growth requires high temperature and high atmospheric gas. In the case of ZnSe, in order to prevent sublimation, a pressure of several tens to 50 atm of an inert gas must be applied, and a high temperature of 1520 ° C. is necessary. For this reason, there are many technical difficulties, and the growth apparatus becomes extremely complicated, which makes it difficult to grow a single crystal having a low crystal defect density, and has not been completed as a practical growth method.

Further, as a more fundamental reason, ZnSe has a material property that is more likely to introduce crystal defects than Si or GaAs. That is, since the critical stress for generating dislocations and the mobility of dislocations are small, dislocations are easily generated and propagated from the outer periphery of the crystal due to thermal stress generated when the grown crystal is cooled, etc., resulting in an increase in transfer density. In addition, since the stacking fault energy is small, it is possible to easily increase the twin density.

Various growth methods other than the high-pressure Bridgman method have been proposed so far, but for the above reasons, they have not been completed as a practical method.

(Problems to be Solved by the Invention) It is conventionally known that there is a method of adding impurities at a high concentration in order to suppress the generation and propagation of dislocations. However, the guiding principle for finding impurities suitable for this method has not yet been established. For example, in GaAs
Addition of (indium) is effective for suppressing the generation and propagation of dislocations, but addition of B (boron) and Al (aluminum), which are homologous to the periodic table, significantly reduces the effect. Also S (sulfur)
Has a remarkable effect, but Se (selenium) and Zn have no effect. However, Zn has a remarkable suppressing effect on InP. On the other hand, the critical concentration required to have the suppressing effect differs depending on the type of impurities. For example, Ga
In As, S has a remarkable effect at a concentration of 1 × 10 ¹⁸ atoms / cm ³ or more, but in In, the critical value is 1 × 10.
²⁰ pieces / cm ³ . Moreover, the impurity has a segregation coefficient, but its value is unknown. When the segregation coefficient has a value significantly different from 1, the impurity concentration significantly changes depending on the site of the grown single crystal due to the impurity segregation phenomenon, causing the generation of dislocations.
There is a problem that the dislocation density of the entire grown crystal cannot be reduced because there is a crystal part whose concentration is below the concentration that suppresses the propagation.

In view of such drawbacks of the conventional method, the present invention provides ZnSe.
It is an object of the present invention to provide a method capable of growing a ZnSe single crystal having a low defect density by improving the material characteristics in which crystal defects are easily introduced by appropriately adding impurities to the ZnSe single crystal.

(Means for Solving Problems) As described above, there are very few data for determining what kind of impurities should be added and how much (concentration) to reduce the crystal defect density. Therefore, it is usually determined empirically, and it has not been known which element is the most suitable impurity in the case of ZnSe.

In the present invention, since ZnSe single crystal growth having a low crystal defect density is performed, one or two kinds of S and O are added as impurities in a range of 5 × 10 ¹⁷ pieces / cm ³ to 5 × 10 ¹⁹ pieces / cm ³ . It is characterized in that it is added internally to grow a single crystal.

The principle of the present invention will be described below. FIG. 1 is a graph showing an example of the correlation between the concentration of added impurities and the defect density, which has an effect of suppressing the generation (and propagation) of crystal defects. As is clear from the figure, the concentration of added impurities is 1 × 10 ¹⁸ /
A cm ³ or more has a remarkable effect, and a low defect density single crystal can be grown. The suppression effect differs depending on the type of impurities.

Hereinafter, although specifically described based on Examples, the method of the present invention is not limited to ingot-shaped single crystal,
It can also be applied to an epitaxially grown thin film single crystal.

(Example 1) First, 99.999% of raw material ZnSe powder was placed in a vacuum for about 105
Sublimation treatment was performed at 0 ° C. for 24 hours to recrystallize. This was loaded with a small amount of purified ZnS powder into a high-purity graphite crucible having an inner diameter of about 5 mm and a height of about 70 mm. Here, the inside of the crucible is tapered, and the tip of the crucible is provided with a thin tube portion having an inner diameter of 1 mm and a length of 5 mm to facilitate single crystal formation. Next, the crucible was placed in a high temperature high pressure electric furnace at a position having a temperature gradient of 100 ° C./cm with a melting point of 1515 ° C. After exhausting the electric furnace, high-purity Ar gas was added to about 70
It was filled with kg / cm ² . Next, the maximum temperature was raised to about 1650 ° C. and kept in the molten state for about 30 minutes. Next, the crucible was lowered at a speed of 4.5 mm / hr to grow crystals from the lower part of the crucible.

The crystal having a diameter of about 5 mm and a length of 40 mm obtained as described above was a substantially transparent single crystal, and the twin density was considerably reduced as compared with the case where S was not added. Also, a sample cut into a wafer is etched in a boiling saturated NaOH solution to obtain an etch pit density (corresponding to the dislocation density).
When compared with the case where S was not added, it was decreased by two digits or more.

Impurity analysis of S concentration in the crystal revealed that it was about 5 × 10 ^18.
The number was pieces / cm ³ . When the change in the defect density with respect to the S concentration was examined, the defect density reducing effect was observed at a concentration of 1 × 10 ¹⁸ defects / cm ³ or more. On the other hand, when the S concentration was 5 × 10 ¹⁹ pieces / cm ³ or more, polycrystallization proceeded due to compositional supercooling. Therefore, the S concentration is 1 × 10 ¹⁸ pieces / cm ³ to 5
A value of × 10 ¹⁹ pieces / cm ³ was suitable.

(Example 2) A purified ZnSe powder to which a small amount of purified ZnO powder was added and mixed in various proportions was charged into a high-purity graphite crucible, and a single crystal was grown in the same manner as in Example 1.
When the obtained single crystal was evaluated in the same manner as in Example 1, the defect density reducing effect began to appear at an O concentration of 5 × 10 ¹⁷ / cm ³ or more. On the other hand, 5 × 10 ¹⁹ pieces / cm ³ or more of O
At the concentration, polycrystallization proceeded remarkably. Therefore, the optimum O concentration is 5 × 10 ¹⁷ pieces / cm ³ to 5 × 10 ¹⁹ pieces / cm ³
Was within the range of.

Example 3 Purified ZnSe powder, to which a small amount of purified ZnS powder and purified ZnO powder were added and mixed in various proportions, was charged into a high-purity graphite crucible, and a single crystal was grown in the same manner as in Example 1. did. When the obtained single crystal was evaluated in the same manner as in Example 1, 5 × 10 ¹⁷ pieces / cm ³ or more (S +
The effect of reducing the defect density was observed at the O) concentration. On the other hand, 5 × 1
At a (S + O) concentration of 0 ¹⁹ pieces / cm ³ or more, polycrystallization markedly progressed. Therefore, the optimum (S + O) concentration is 5
It was in the range of × 10 ¹⁷ pieces / cm ³ to 5 × 10 ¹⁹ pieces / cm ³ .

(Effect of the invention) By using the method of the present invention, a large-sized ZnSe single crystal having a low crystal defect density can be obtained, so that it is of great value as an epitaxial growth substrate or an epitaxial thin film growth method for producing a blue light emitting device. .

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an example of the relationship between the impurity concentration and the defect density, which has an effect of suppressing the generation (and propagation) of crystal defects.

Claims (1)

[Claims] 1. In the growth of a ZnSe (zinc selenide) single crystal, one of S (sulfur) and O (oxygen) as impurities, or simultaneously, 5 × 10 ¹⁷ pieces / cm 3.
^A method of growing a ZnSe single crystal, characterized in that it is added within a range of ³ to 5 × 10 ¹⁹ pieces / cm ³ .