JPH11228299A - Single crystal of compound semiconductor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a single crystal of a highly pure compound semiconductor of group II-IV compounds such as ZnSe and CdTe, having <=1×10<15> cm<-3> concentration of each of Na, Li and a carrier. SOLUTION: Crystal growth is stopped at a stage at a prescribed solidified proportion at which the each concentration of Na, K and a carrier is <=1×10<15> cm<-3> at the solid-liquid interface between a single crystal and a raw material molten liquid at which the crystal growth is carried out, and immediately the cooling of the crystal is started, in a liquid-encapsulated Czochralski method, a Bridgeman method or a temperature gradient slow cooling method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor single crystal and a method for producing the same, and particularly to a high purity ZnSe,
The present invention is applied to a compound semiconductor single crystal including a Group 12 (2B) element and a Group 16 (6B) element such as ZnTe and CdTe (hereinafter referred to as “II-VI compound semiconductor single crystal”) and its manufacture. And effective manufacturing techniques.

[0002]

2. Description of the Related Art A group II-VI compound semiconductor single crystal typified by zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium telluride (CdTe), etc. has a higher luminous efficiency than silicon (Si). Therefore, it is expected to be applied to a light emitting / receiving element, a low noise amplifying element, and the like.

In particular, CdTe has a zinc-blende structure, an energy gap of 1.4 eV, can conduct p and n-type conduction, and has a substrate for epitaxial growth of an infrared detecting element, a solar cell, visible light, It is used for infrared sensors, radiation detecting elements for γ-rays, X-rays and the like, non-destructive detecting elements, and the like.

The characteristics of these devices often depend on the purity of the compound semiconductor single crystal forming the substrate.
There is a demand to obtain a compound semiconductor single crystal with a high purity in order to improve the performance of the device. For example,
In CdTe, it was necessary to lower the single crystal carrier concentration in order to increase the transmittance.

Conventionally, these II-VI group compound semiconductor single crystals have been prepared by a Bridgman method, a gradient freezing method (GF method), and a vertical temperature gradient cooling method (Vertical Gradient Freezing Method: V).
GF method) and the like.

In the Bridgman method, the twelfth (2)
A compound semiconductor single crystal is grown by dissolving a raw material composed of a Group B) element and a Group 16 (6B) element in a crucible and moving it in a temperature gradient of 10 to 50 ° C./cm to a lower temperature side.

In the temperature gradient slow cooling method, the twelfth (2)
The compound semiconductor single crystal is grown by changing the temperature profile without moving the crucible itself in which the raw material comprising the group B) element and the group 16 (6B) element is melted.

In these crystal growth methods, the defect density in the crystal is reduced by optimizing the growth conditions such as reducing the temperature gradient in the melt and reducing the temperature fluctuation in the melt. Was reduced.

[0009]

However, in the conventional method for producing a compound semiconductor single crystal, a high-purity single crystal having a reduced impurity concentration so as to satisfy the demands cannot be obtained.

For example, when a single crystal of CdTe is grown by the conventional VGF method, the carrier concentration required for realizing a sufficient transmittance and the like is 1 × 10 ¹⁵ cm ⁻³ or less, and the Na concentration and A high-purity P-type crystal having a Li concentration of 1 × 10 ¹⁵ cm ⁻³ or less could not be obtained.

A conventional liquid-encapsulated Czochralski method (LEC)
CdTe using the vertical Bridgman method (VB method), the vertical temperature gradient slow cooling method (VGF method), the horizontal Bridgman method (HB method) or the horizontal temperature gradient slow cooling method (HGF method)
Is grown by using up all the raw materials charged in the crucible or boat (that is, the solidification rate g = 1.0).
(100%)).

However, studies by the present inventors have revealed that these conventional methods cannot sufficiently purify a single crystal.

That is, the crystal growth is continued until all the materials in the crucible are used up by the VGF method, for example, and the P-type CdT
When a single crystal of e was grown, the carrier concentration was 1 × 10 ¹⁵ cm ⁻³ or more, as shown in FIG. 5, and the carrier concentration could not be reduced.

Focusing on the residual impurities in the CdTe single crystal, as shown in FIG.
The concentration of Na and Li as mold carriers is 1 × 10 ¹⁵ cm ⁻³
This is what SIMS (Secondary Ion Mass Spect
(rometer: secondary ion mass spectrometry), the result was analyzed by CdTe single crystal.

The present invention has been devised as a result of research in view of the above circumstances, and provides a compound semiconductor single crystal having a reduced residual impurity concentration and a low carrier concentration, and a method for producing the same. It is intended for.

[0016]

In order to achieve the above object, in the compound semiconductor single crystal according to the present invention, the concentration of Na is set to 1 × 10 ¹⁵ cm ⁻³ or less. When the concentration of Na is 1
× 10 ¹⁵ cm ^-3 or less and the concentration of Li is 1 × 10 ¹⁵ c
m ⁻³ or less, the concentration of Na is 1 × 10 ¹⁵ cm ⁻³ or less, the concentration of Li is 1 × 10 ¹⁵ cm ⁻³ or less, and the carrier concentration is 1 × 10 ¹⁵ cm ⁻³ or less. did.

Incidentally, the compound semiconductor is a compound of the twelfth of the periodic table.
It is made of a (2B) group element and a 16 (6B) group element, and can include at least one of Cd, Zn, and Te.

On the other hand, according to the method of manufacturing a compound semiconductor single crystal according to the present invention, the concentration of Na in the single crystal is 1 × at the solid-liquid interface between the single crystal on which the crystal is growing and the raw material melt.
Crystal growth was interrupted at the stage of a predetermined solidification rate of 10 ¹⁵ cm ^-3 or less, and cooling of the crystal was started immediately.

At the solid-liquid interface between the single crystal on which the crystal is growing and the raw material melt, a predetermined solidification rate in which the concentration of Na and Li in the single crystal is 1 × 10 ¹⁵ cm ⁻³ or less, respectively. The crystal growth was interrupted at the stage of and the cooling of the crystal was started immediately.

At the solid-liquid interface between the single crystal on which the crystal is growing and the raw material melt, the Na, Li
The crystal growth was interrupted at the stage of the predetermined solidification rate in which the carrier concentration was 1 × 10 ¹⁵ cm ⁻³ or less, and the cooling of the crystal was started immediately.

The single crystal is grown by a liquid-sealed Czochralski method (LEC method), a vertical Bridgman method (VB method), a vertical temperature gradient slow cooling method (VGF method), or a horizontal Bridgman method (HB method). Method or the horizontal temperature gradient slow cooling method (HGF method).

The following is a brief description of the contents of studies and the progress of research by the present inventors before reaching the present invention.

The present inventors have conducted research on single crystals such as CdZnTe. As a result, when the crystal growth of the raw material charged in the crucible or the boat is continued until the solidification rate g = 1.0, the carrier concentration, Na, Li Concentration of 1 × 10 ¹⁵
It is considered that the segregation coefficient k of residual impurities such as Na and Li present in the raw material melt in the crucible or the boat is k <1 and the diffusion rate is C < ^-3.
Since it is faster than d, Zn, Te, etc., CdZn
It was presumed that Na, Li, etc. would be diffused over the entire region of a single crystal such as Te.

Then, CdZnT is formed by VGF method or the like.
A plurality of single crystals such as e were grown, analyzed by SIMS, and the relationship between the concentration of residual impurities and the carrier concentration and the crystal quality were considered. It was confirmed that it is effective to reduce the concentration of Na and Li among the impurities to 1 × 10 ¹⁵ cm ⁻³ or less.

Further, as a result of repeated studies on the relationship between the concentrations of Na and Li and the solidification rate of the crystal to be grown, the solidification rate g was set to 1.0 before all the raw materials charged in the crucible or boat were used up. (100%) The growth of the crystal is interrupted at a stage of a predetermined solidification rate of less than 100%, and the crystal is immediately cooled to suppress the diffusion of Na and Li into the crystal,
Thus, the present invention has been completed based on the finding that the concentrations of Na and Li can be suppressed to 1 × 10 ¹⁵ cm ⁻³ or less.

According to the present invention, the entire II-VI compound semiconductor single crystal can be highly purified. Therefore, if these compound semiconductor single crystals are used, the characteristics of various semiconductor devices can be improved. Can be expected.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example of an embodiment of the present invention, a case where a CdTe single crystal is grown by the VGF method to which the manufacturing method according to the present invention is applied will be described with reference to FIGS. I do.

FIG. 1 is an explanatory view showing a process of growing a CdTe single crystal by the VGF method.

First, a crucible is filled with a predetermined material for growing a CdTe crystal, and is placed at a predetermined position in a high-pressure vessel provided with a heater.

Then, the heater is driven to raise the temperature to 1100 ° C., which is the temperature at which the raw material is sufficiently melted, over 2 hours, and the temperature is maintained for 48 hours to homogenize the raw material melt.

Thereafter, required in the VGF method,
A temperature profile in which the lower portion has a low temperature is set, crystal growth is started, and the temperature is increased at a rate of 0.1 ° C./hr for 200 hours (2 hours).
00 hrs) Continue crystal growth.

After the elapse of 200 hours, the crystal growth process is interrupted, the process proceeds to a cooling process, and cooling is performed for 8 hours to complete the growth of the single crystal.

According to this embodiment, the crucible contains Na, L
Although the raw material melt containing residual impurities such as i remains, the crystal growth is interrupted when the raw material melt is not completely used up. Diffusion into the CdTe single crystal can be effectively suppressed, and the concentrations of Na and Li and the carrier concentration can be reduced to 1 × 10 ¹⁵ cm ⁻³ or less.

Incidentally, conventionally, all of the raw material melt in the crucible was used for crystal growth over 250 hours. Therefore, Na, Li, and the like as residual impurities diffused throughout the CdTe single crystal and could not be highly purified.

The relationship between the concentrations of Na and Li and the solidification rate g of the crystal in the present invention is as shown in FIG.

That is, when the solidification rate is 1.0, the concentrations of Na and Li become extremely high.
The method of interrupting the crystal growth process when the a and Li concentrations are 1 × 10 ¹⁵ cm ⁻³ or less achieves high purity by suppressing the diffusion of impurities into the single crystal.

The time at which the crystal growth process is interrupted depends on the type of compound semiconductor to be grown, the method of growing the crystal, the conditions for the growth, and the like. Therefore, it is desirable to repeat experiments and determine an appropriate crystal growth interruption time that satisfies these conditions.

Here, FIGS. 3 and 4 show the analysis results of the CdTe single crystal obtained by the above-described crystal growth process.

FIG. 3 is a graph showing the P-type carrier concentration corresponding to the crystal position of the CdTe single crystal, where ● indicates a single crystal according to the present invention, and ○ indicates a single crystal according to the prior art. As is apparent from FIG. 3, the carrier concentration of the single crystal grown according to the present invention is reduced to 1 × 10 ¹⁵ cm ⁻³ or less over the entire region of the crystal, which is lower by one order of magnitude compared to the prior art. It can be seen that the carrier concentration is increased.

FIG. 4 is a graph showing Na,
5 is a graph showing a relationship between a Li concentration value and a carrier concentration, wherein two crystals 1 and 2 grown according to the present invention as samples and two crystals 1 and 2 grown according to the prior art.
Are plotted by measuring the Na concentration and the Li concentration for each.

As is apparent from FIG. 4, the CdTe single crystal grown according to the present invention has a significantly lower concentration of Na and Li, which are the main residual impurities of P-type CdTe, than the single crystal according to the prior art. You can see that

As described above, the CdTe single crystal according to this embodiment has a Na and Li concentration of 1 × 10
^{Since the} purity can be reduced to ¹⁵ cm ^-3 or less and high purity can be expected, the characteristics of various devices manufactured using the CdTe single crystal can be improved.

In the above embodiment, the growth of CdTe single crystal has been described. However, the present invention is not limited to this, and is applicable to general II-VI compound semiconductor single crystals such as CdZnTe and CdZn. is there.

In the above embodiment, the VGF method is exemplified as the crystal growing method. However, the crystal growth method is not limited to this, and the liquid sealing Czochralski method (LEC method), the vertical Bridgman method (VB method). , Horizontal Bridgman method (HB
Method) or a horizontal temperature gradient slow cooling method (HGF method).

[0045]

According to the present invention, the Na in the single crystal is formed at the solid-liquid interface between the single crystal on which the crystal is growing and the raw material melt.
The crystal growth was interrupted at the stage of the predetermined solidification rate of 1 × 10 ¹⁵ cm ⁻³ or less and the cooling of the crystal was started immediately. Purification can be achieved, and if these compound semiconductor single crystals are used, there is an excellent effect that characteristics of various semiconductor devices can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a crystal growing process by a method for producing a compound semiconductor single crystal according to the present invention.

FIG. 2 is a graph showing a relationship between Na and Li concentrations and a solidification rate in the method for producing a compound semiconductor single crystal according to the present invention.

FIG. 3 shows a CdTe single crystal grown by the method of manufacturing a compound semiconductor single crystal according to the present invention and Cd according to the prior art.
4 is a graph showing an analysis result of a carrier concentration of a Te single crystal.

FIG. 4 shows a CdTe single crystal grown by the method of manufacturing a compound semiconductor single crystal according to the present invention and Cd according to the prior art.
4 is a graph showing analysis results of the carrier concentration of a Te single crystal and the impurity concentration analyzed by SIMS.

FIG. 5 is a graph showing an analysis result of a carrier concentration of a CdTe single crystal grown by a conventional technique.

FIG. 6 is a graph showing the results of analyzing the carrier concentration of a CdTe single crystal grown by a conventional technique and the impurity concentration analyzed by SIMS.

Claims (10)

[Claims] 1. A compound semiconductor single crystal wherein the concentration of Na is 1 × 10 ¹⁵ cm ^-3 or less. 2. A compound semiconductor single crystal wherein the concentration of Na is 1 × 10 ¹⁵ cm ^-3 or less and the concentration of Li is 1 × 10 ¹⁵ cm ^-3 or less. 3. The method according to claim 1, wherein the concentration of Na is 1 × 10 ¹⁵ cm ^-3 or less, the concentration of Li is 1 × 10 ¹⁵ cm ^-3 or less, and the carrier concentration is 1 × 10 ¹⁵ cm ^-3 or less. Characteristic compound semiconductor single crystal. 4. The method according to claim 1, wherein the compound semiconductor is a compound of the periodic table 12 (2).
The compound semiconductor single crystal according to any one of claims 1 to 3, comprising a Group B) element and a Group 16 (6B) element. 5. A twelfth aspect of the periodic table constituting the compound semiconductor.
As a group (2B) element and a group 16 (6B) element, C
The compound semiconductor single crystal according to claim 4, comprising at least one of d, Zn, and Te. 6. At the solid-liquid interface between the single crystal on which the crystal is growing and the raw material melt, the concentration of Na in the single crystal is 1 ×.
A method for producing a compound semiconductor single crystal, wherein crystal growth is interrupted at a stage of a predetermined solidification rate of 10 ¹⁵ cm ^-3 or less, and cooling of the crystal is started immediately. 7. At a solid-liquid interface between a single crystal on which crystal growth is taking place and a raw material melt, a predetermined solidification ratio in which the concentrations of Na and Li in the single crystal are each 1 × 10 ¹⁵ cm ⁻³ or less. Wherein the crystal growth is interrupted at the stage of and the cooling of the crystal is started immediately. 8. At a solid-liquid interface between a single crystal on which crystal growth is being performed and a raw material melt, a predetermined concentration of Na, Li and carrier in the single crystal is 1 × 10 ¹⁵ cm ⁻³ or less, respectively. A method for producing a compound semiconductor single crystal, characterized by interrupting crystal growth at the stage of solidification rate and immediately starting cooling of the crystal. 9. The method for growing a single crystal according to the present invention includes a liquid-sealed Czochralski method (LEC method), a vertical Bridgman method (VB method), a vertical temperature gradient cooling method (VGF method), and a horizontal Bridgman method (HB method). 7. The method according to claim 6, wherein the method is one of a horizontal temperature gradient slow cooling method (HGF method).
A method for producing a compound semiconductor single crystal according to any one of claims 1 to 8. 10. The method of growing a single crystal according to the vertical Bridgman method (VB method), the vertical temperature gradient slow cooling method (VGF method).
9. The method for producing a compound semiconductor single crystal according to claim 6, wherein the method is any one of a horizontal Bridgman method (HB method) and a horizontal temperature gradient slow cooling method (HGF method). .