JPH0751471B2 - Method for producing compound semiconductor single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for producing a compound semiconductor single crystal. More specifically, by improving the vertical Bridgman method and controlling the vapor pressure closely, the stoichiometry is excellent, and there is little deviation from perfection, and a uniform and uniform low defect compound semiconductor single The present invention relates to a method for producing a crystal, particularly a compound semiconductor single crystal containing a low melting point element component, and an apparatus therefor.

2. Description of the Related Art II-VI group compound semiconductors are direct transition type
It is known that high-efficiency luminescence is generated by excitation with an electron beam, and in the field of optoelectronics II
Extensive research has been conducted as a material that can realize a wide liquid length range and a light-receiving element, which is not possible with IV compound semiconductors.

However, since these II-VI group compound semiconductors have a large band gap and have a self-compensating effect, they cannot form a PN junction according to a usual method except for CdTe, which is a big problem in application. . Among them, CdTe which can realize a PN junction by a normal method, mainly used in the field of optoelectronics as a γ-ray or X-ray detector or as a mixed crystal with HgTe, is used as an infrared detector, a CCD or the like. It is used for fabrication, and also used for fabrication such as CdS / CdTe solar cells combined with CdS, and these are promising application fields utilizing the characteristics of CdTe.

By the way, in order to manufacture the above-mentioned various devices of the compound semiconductor CdTe, it is necessary to manufacture a CdTe single crystal having a low dislocation density and a low defect. Since this one has various characteristics different from a single element semiconductor such as Si like a general compound semiconductor, a single crystal manufacturing technique different from these is required. For example, the Czochralski method (CZ method) and the floating zone method (FZ method) are generally used for Si, but strict control of the composition is required for CdTe and the critical shear stress at high temperatures is small. However, it has various subtle technical problems such as dislocations easily entering due to thermal strain.

That is, even if the atomic weight ratios of the constituent elements are accurately weighed and reacted in order to grow a high-purity single crystal, the obtained single crystal product does not necessarily have the composition of the intended stoichiometric ratio.
Therefore, it is necessary to devise a single crystal growth operation in consideration of not only the problem of stoichiometry in terms of chemical analysis but also the deviation from the crystal perfection. Therefore,
Various crystal growth methods are known in order to make the generated CdTe single crystal as high as possible in perfection. Among them, as a single crystal growth method for II-VI group compound semiconductors such as CdTe, vapor pressure control is easy. Therefore, the Bridgeman method (vertical and horizontal Bridgman method) is widely used.

When the CdTe single crystal is grown by the Bridgman method, particularly the vertical Bridgman method, conventionally, for example, an apparatus as shown in FIGS. 2 (a) and 2 (b) is used. For example, when a single crystal of CbTe is produced by using the vertical Bridgman method, it is necessary to grow while controlling the partial pressure of one of the components (the partial pressure of Cd or Te). For example, an n-type or p-type crystal having a constant resistance value is extremely important from the viewpoint of forming during the growth process.

First, in the apparatus shown in FIG. 2 (a), a raw material 2 for single crystal growth (eg, Te and Cd having a purity of 6 nines in an experimental scale of about 0.1 mol each is provided in the lower portion of a cylindrical reaction tube 1 having a closed lower end. On the other hand, the upper space is filled with excess Cd or Te3 in advance (generally about 10 μg to several mg), and the reaction tube 1 is sealed in this state, and a heater provided outside the reaction tube (see FIG. The single crystal 4 is grown by moving the inside of the furnace maintained at a predetermined temperature distribution (one example is shown on the left side of the figure) by a not-shown) at a predetermined speed. The melt 5 is at a high temperature of 1150 ° C, and the grown single crystal 4 is 950
The growth of the single crystal occurs at the solid-liquid interface 6 near the melting point (1092 ° C.) in the transient region between the high temperature portion and the low temperature portion.

This method vaporizes a very small amount of Cd or Te for controlling vapor pressure, which is co-encapsulated together with the raw material, in the space above the growth tube (reaction tube), and adds Te or the volume of the cavity (V) and excess Te or
By controlling the molar amount (n) of Cd, it is intended to control each partial pressure according to the equation of state of gas: PV = nRT (where R is the molar gas constant and T is the temperature of the growth chamber). is there.

In this method, as described above, the space above the reaction tube 1 (volume V)
Stoichiometry is maintained by dissolving excess Cd or Te enclosed in the crystal melt in the crystal melt according to the solid solubility of each component element in the CdTe during crystal growth. However, as a result, the number of moles of trace Cd or Te in the headspace decreases, and the gas equation of state PV = nR correspondingly decreases.
As the pressure P in the space decreases with T, it becomes difficult to control the physical properties. This tendency becomes more remarkable as the excess amount of Cd or Te that should be simultaneously encapsulated with the raw material decreases, especially when Cd or Te
Alternatively, when a precipitate of Te is produced, a crystal having uncontrolled physical properties with poor reproducibility may be obtained.

On the other hand, in the apparatus shown in the attached FIG. 2 (b), the upper part of the reaction tube 1 is composed of a capillary 7, and an excess amount of Cd or Te is present as a condensed phase 8 in the apparatus shown in FIG. 2 (a). As in the case, a single crystal is grown. In this example, a single crystal is grown by setting the temperature distribution as shown on the right side of the figure in a furnace equipped with heaters A and B and lowering the reaction tube 1 downward at a predetermined speed.

This method can be expected to be better than the method of FIG. 2 (a) in that the condensed phase 9 is used, but it still has the following problems. That is, since the condensed phase 9 is above the growth chamber and the Cd and Te vapors are heavy, the Cd or Te gas from the growth chamber trying to form the condensed phase does not flow into the upper condensed phase due to gravity. Could not be reached, resulting in the formation of a new condensed phase below the condensed phase 9 and near the growth chamber. This leads to expansion of the region where strict temperature control should be performed, and makes it difficult to detect the correct condensed phase temperature. This makes even tighter vapor pressure control significantly more difficult.

Problems to be Solved by the Invention As described in detail above, the compound semiconductor CdTe is the only compound semiconductor that can form a PN junction in the II-VI group compound semiconductors by a normal method, and the III-V group compound semiconductor It has attracted attention because it is useful as a semiconductor material for producing light emitting and light receiving elements in a wavelength range that cannot be realized by semiconductors. However, except that a thin film can be easily formed, there are various problems that must be solved in order to obtain a CdTe single crystal as a high-quality product. In particular, it is relatively difficult to form a low-defect bulk single crystal with excellent stoichiometry, and in particular, Cd and Te have a low melting point compared to the single crystal growth temperature or more accurately the vapor pressure control temperature. Therefore, it is difficult to control the vapor pressure during single crystal growth.

For this reason, conventionally, as described above, excess Cd or Te is enclosed as a gas phase in the empty tube of the reaction tube, or the upper part of the reaction tube is configured with a capillary or the like, and inside the capillary during single crystal growth. Attempts have been made to have Cd or Te present as a condensed phase. However, none of these prior art methods is sufficient, and further improved methods are desired to be developed.

Therefore, the object of the present invention is to improve the conventional Bridgman method, excellent in stoichiometry, small deviation from the completeness of crystal, uniform and uniform compound semiconductor,
In particular, CdTe containing a component having a melting point below the vapor pressure control temperature
Another object of the present invention is to provide a method for manufacturing a bulk single crystal of the above.

Means for Solving the Problems In view of the conventional situation of the CdTe single crystal growth method and apparatus as described above, the present inventor has improved the various drawbacks thereof to obtain a desired high-quality single crystal such as CdTe. As a result of various investigations and studies, the storage part for Cd or Te for vapor pressure control should be placed below the growth chamber, while the raw material for single crystal growth should be placed in another storage container and placed above. Has been found to be extremely effective for achieving the above object, and completed the present invention.

That is, the method for producing a CdTe single crystal of the present invention includes a container for storing a single crystal growth raw material in the upper crystal growth chamber and a lower vapor pressure control component element storage chamber which are communicated by a communication hole, and a vapor pressure control It is intended for a method of encapsulating an element for use and moving it in a furnace in which a predetermined temperature distribution is set to perform single crystal growth while controlling the vapor pressure.

The compound semiconductor single crystal that can be produced by the method of the present invention contains, as a component, a low melting point element that becomes a liquid state particularly under its synthesis temperature (growth temperature) or vapor pressure control temperature, such as Cd or Te. They may be related single crystals, mixed crystals, or those containing a dopant. Therefore, in the present specification, the term "single crystal" includes the above-mentioned mixed crystals and those containing a dopant.

In the method of the present invention, the vapor pressure control (partial pressure control) component is
When Cd (bp = 764.3 ℃), the partial pressure control temperature and control partial pressure are 758K to 124.2K, respectively, depending on the physical properties of the final single crystal.
And 1.3 × 10 ^-2 atm (about 10 Torr) ~ 6 atm (about 4560 Torr)
Is advantageous. On the other hand, when the vapor pressure control (partial pressure control) component is Te (bp = 989.8 ° C), the partial pressure control temperature and control partial pressure are 904K to 1266K and 1.3 × 10 ^-2 atm (about 10 Torr) to 1 atm, respectively. The range of (about 760 Torr) is the main feature of the present invention.

The above method according to the present invention can be implemented by the following device. That is, the apparatus is provided with a vapor pressure control component storage chamber disposed below, a growth chamber communicating with the storage chamber by a communication means, and a single crystal growth raw material storage container disposed in the growth chamber. The present invention relates to an improvement of the vertical Bridgman apparatus, which comprises a reaction tube and a furnace provided with a heater arranged so as to surround the reaction tube on the outer side thereof.

The feature of this apparatus is that a component element storage portion for controlling vapor pressure (partial pressure) is provided in the reaction tube below the crystal growth chamber. Therefore, the growth chamber and the storage chamber need to be spatially communicated with each other, and for that purpose, a communication means such as a capillary or at least one pinhole is provided between them.

The growth chamber may be integrated with the raw material storage container to have a concentric cylindrical double tube structure, and may be connected to the partial pressure control element storage chamber via the space and the communication means. . In any case, the storage chamber is provided below the growth chamber,
It suffices that the components are connected by the communication means, and various modes other than the above are possible.

Here, when the growth chamber and the raw material container are separately formed,
When the container is housed in the growth chamber, it is necessary to provide a space so that the partial pressure control element gas supplied to the growth chamber through the communication means can freely flow in and out of the entire growth chamber or the space above the raw material container. is there. For this purpose, various other means such as providing at least three legs on the bottom of the raw material container, or arranging a cylindrical member having a large number of holes on the side as a support at the bottom of the container is used. You can

In this apparatus, the material container can be made of carbon-coated quartz, pyrolytic boronized boron (PBN), or any other known material that does not react with the material under growth conditions.

When growing a CdTe single crystal with this device, the vapor pressure control component elements and the single crystal growth raw material are put into each storage chamber (or storage container) of the reaction tube, and if necessary, exhaust gas or inert gas Fill and seal the reaction tube. On the other hand, the heater of the furnace is operated to fix the above-mentioned reaction tube at a predetermined position in the furnace in which a predetermined temperature distribution is set, and this state is maintained until the temperature in the reaction tube is sufficiently balanced, and then the predetermined temperature is maintained. The reaction tube or furnace is moved at a speed to grow a single crystal.

According to this method, the temperature control of the partial pressure controlling component element is
For example, it can be realized by obtaining accurate temperature information by a temperature detector (such as a thermocouple) attached to the lower end of the storage chamber and controlling the heater for heating the vapor pressure control unit based on this information. It is also possible to connect the heater to a computer and automatically control the heater in response to a signal from the former.

Action Strict vapor pressure control is required when manufacturing compound semiconductor single crystals, especially when it contains a low melting point element that melts at the growth temperature or vapor pressure control temperature, or when high dissociation occurs at these temperatures. When a component element having an equilibrium vapor pressure is contained, the conventional method cannot be used as it is, and various improvements are required.

Among the above examples, especially when low melting point component elements are involved,
Since it melts during the growth operation, its flow or once vaporized, or the vaporized element from the raw material melt is condensed to broaden the region to be temperature controlled, and highly precise strict temperature control, As a result, it becomes extremely difficult to accurately control the vapor partial pressure in the growth chamber and to control the stoichiometry of the grown crystal and the crystal perfection.

However, the problems encountered in performing the single crystal growth by the conventional vertical Bridgman method as described above are caused by carrying out the single crystal growth by the method according to the present invention, or by utilizing the apparatus of the present invention. This has almost solved the problem and made it possible to obtain satisfactory results.

In the present invention, in the vertical Bridgman method, the chamber for containing the vapor pressure control component element is arranged below the growth chamber. As a result, it is possible to completely prevent the vapor pressure control region from expanding under the influence of the weight and gravity of the vaporized element component, and limit the existing position of the melted component element to a certain place. Therefore, the temperature detection area and the temperature control area are always limited to a certain narrow area, and strict temperature control can be performed.
This is an important factor in realizing strict partial pressure control. Thus, the temperature control of the partial pressure control region (condensed phase) becomes strict through the single crystal growth, for example,
The saturated vapor pressure of each element, which is determined by the temperature of the condensed phase of Cd or Te, can be maintained in the growth chamber, and as a result, the physical properties of the grown single crystal can be accurately and strictly controlled.

Further, the partial pressure control component element storage chamber and the growth chamber arranged below are preferably communicated with each other by a small hole such as a capillary, a pinhole or the like through which the gas of the element can pass, and the partial pressure is maintained. The vaporized element from the control chamber is sufficiently supplied to the growth chamber, and the backflow of the gas component element from the raw material melt to the low temperature portion (that is, the partial pressure control region) is effectively prevented. This is not only a tight control of vapor pressure,
It is possible to improve the quality and yield of the obtained single crystal.

Depending on the type of element, it may be in a boiling state under the vapor pressure control temperature, but in this case as well, since the storage part was provided at the bottom of the growth chamber, the region where the melt was present did not expand, and the vapor pressure It is possible to obtain the advantage that one point is sufficient for the control.

Further, according to the apparatus of this configuration, volatile and heavy impurities move toward the vapor pressure control element storage chamber provided below in the crystal growth process, so that a crystal refining effect can be expected. You can also

Thus, according to the method of the present invention, since it is possible to strictly control the vapor pressure, by properly selecting the vapor pressure during growth, the conductivity type, the physical properties such as the resistance value is sufficiently controlled single crystal Can be obtained with good reproducibility, which can be advantageously used as a material for manufacturing various semiconductor devices. For example, for CdTe, materials for infrared detectors (Cb _x
It is useful as a material for Hg _1-x Te in vapor phase or liquid phase epitaxial growth), γ-ray detector, and solar cell material, and can further improve the reliability and performance of these devices. .

Examples Hereinafter, the method of the present invention and an apparatus for carrying out the method will be described in more detail and concretely by examples. However, the scope of the present invention is not limited by the following examples.

Example 1 A preferred embodiment of an apparatus for carrying out the method of the present invention is shown in the attached FIG. 1 together with a temperature distribution curve in a furnace by a schematic sectional view. As is apparent from the figure, this embodiment is a reaction composed of a growth chamber 10 arranged above, a vapor pressure control component element storage chamber 11 arranged below it, and a small hole 12 communicating these. Tube 13 (quartz tube) and housed in the growth chamber,
It comprises a raw material container 14 (carbon-coated quartz) for containing a growth raw material, and a furnace provided with heaters 15 and 16 provided outside the reaction tube 13 so as to surround the same. The heater 15 operates to form a single crystal growth temperature distribution in the furnace, while the heater 16 determines the vapor pressure control temperature. The heater 16 has a thermocouple attached to the lower end of the storage chamber 11.
Temperature information from 17 is input via a computer, and the set temperature can be automatically maintained with high accuracy.

Here, the crystal growth temperature gradient is determined by T ₁ and T _2, and is adjusted so that a gentle temperature gradient is obtained between T ₂ and T ₃ . That is, in between T _2, T ₃ is controlled so as not to become T ₃ or lower. Note that this is not the case below the vapor pressure control unit.

Using the apparatus shown in FIG. 1, the raw material of CdTe were charged into storage vessel (boat) 14, whereas the storage room 11 is charged with Cd purity 6 Nine was replaced by a high-purity Ar, 10 ^{- After} evacuation to ³ Torr or less, the reaction tube 13 was sealed. This is then T ₁ ,
CdTe single crystals were obtained by lowering T ₂ and T ₃ in a furnace adjusted to 1140 ℃, 1050 ℃ and 680 to 910 ℃, respectively, at a speed of 0.3 cm / hour.

The control partial pressure of Cd, the loss amount (transport amount) and the resistance value of CdTe during the growth operation of this CdTe single crystal were measured. The obtained results are shown in FIGS. 3 and 4 as the relationship between the controlled partial pressure of Cd and the loss amount of the synthetic single crystal CdTe and the relationship between the controlled partial pressure of Cd and the resistance of the synthetic single crystal, respectively.

As is clear from FIG. 3, it is understood that the amount of loss decreases with an increase in the partial pressure in proportion to the −3 power of the Cd partial pressure (P _cd ). On the other hand, from FIG. 4, the n-type at the high P _cd is
Further, it can be seen that the p-type is obtained at a low place and the resistance value (ρ: resistivity) of the synthetic single crystal continuously changes with the control of P _cd .

Thus, as is clear from the results shown in FIGS. 3 and 4, according to the method of the present invention, the partial pressure control by the vapor pressure control element storage chamber provided below the growth chamber acts advantageously,
It can be seen that good reproducibility can be secured and maintained in the physical properties and yield of the obtained single crystal.

EFFECTS OF THE INVENTION As described in detail above, according to the method of the present invention, the storage chamber for the vapor pressure control (partial pressure control) component element is provided below the growth chamber, and the storage chamber is communicated by the communication means having the small holes. As a result, the problems found in the conventional method and apparatus could be almost completely solved.

That is, first, even if the vapor pressure control element is melted or boiled at that temperature, the existing region of the condensed phase (or the melted phase) does not spread, and therefore the temperature of only a narrow region is detected and the temperature control is performed with high accuracy, that is, Since the vapor pressure can be controlled, a low defect single crystal having good stoichiometry can be produced.

In addition, since it is possible to control vapor pressure with high accuracy, maintaining this at a predetermined partial pressure allows free formation of single crystals of a specific conductivity type and resistance value, and a large amount of synthetic single crystal loss. It is possible to greatly improve the production yield of a single crystal by reducing the width.

Furthermore, such a structure can reduce volatile and heavy impurities to some extent during the crystal growth, and it has become possible to manufacture a high-purity single crystal.

Thus, the high-purity, high-quality single crystal produced can improve the characteristics of various devices produced by using the single crystal and greatly improve the reliability thereof.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a preferred embodiment of the apparatus of the present invention, and also shows a temperature distribution curve in the furnace, and FIGS. 2 (a) and 2 (b) are conventional. FIG. 3 is a view similar to FIG. 1 for explaining the apparatus of FIG. 3, and FIGS. 3 and 4 show the control partial pressure (P _cd ) and the synthetic single crystal when the single crystal was produced by the method of the present invention. 3 is a graph plotting the relationship with the loss amount (FIG. 3) and the relationship between P _cd and the resistivity ρ (ohm · cm) of the obtained single crystal (FIG. 4). (Main reference numbers) 1,13 …… Reaction tube, 2 …… Raw material, 3 …… Cd or Te, 4 …… Single crystal, 5 …… Raw material melt, 6 …… Solid-liquid interface, 7 …… Capillary, 8 ... Condensed phase (molten phase), 10 ... Growth chamber, 11 ... Storage room, 12 ... Small hole, 14 ... Raw material storage (boat), 15, 16 ... Heater, 17 ... thermocouple

Claims (1)

[Claims] 1. A container for storing a single crystal growth raw material and a vapor pressure control element are enclosed in an upper crystal growth chamber and a lower vapor pressure control component element storage chamber, which are communicated with each other through a communication hole. In a method for producing a compound semiconductor single crystal in which a single crystal is grown while controlling the vapor pressure by moving the vapor in a furnace in which a predetermined temperature distribution is set, the vapor pressure controlling element is Te, and A method for producing a compound semiconductor single crystal, wherein the temperature in the pressure control region is within the range of 904K to 1266K.