JP5050184B2 - Si-doped GaAs single crystal - Google Patents

Description

The present invention relates to a Si-doped GaAs single crystal used as a material for a light emitting / receiving element or the like.

  An n-type conductive GaAs (gallium arsenide) single crystal used as a material for a light emitting / receiving element, a high-speed arithmetic element, a microwave element or the like generally uses Si (silicon) as a dopant to reduce the dislocation density in the crystal. It is manufactured using the horizontal boat method and the vertical boat method. In particular, the vertical boat method has the advantage that not only crystal growth of (100) orientation can be grown, but also a circular and large-diameter crystal can be obtained. The vertical temperature gradient method (VGF method) and the vertical bridge Crystal growth is performed by the Mann method (VB method).

By the way, as the V group element As, which is one of the raw materials of the GaAs single crystal, is a volatile component, B ₂ O ₃ ( oxidation) is used as a liquid sealant for the purpose of preventing dissociation and decomposition from the crystal. Boron) is used. However, when B ₂ O ₃ is used as the liquid sealant, Si as a dopant reacts with B ₂ O ₃ to form silicon oxide (SiO ₂ or SiO), making it difficult to control the Si concentration in the crystal. . For this reason, it is difficult to always stably produce a Si-doped GaAs single crystal having a desired preferable carrier concentration distribution. In order to eliminate this defect, the present inventors proposed a method of growing a Si-doped GaAs single crystal having a desired carrier concentration distribution with good reproducibility using B ₂ O ₃ previously doped with Si oxide ( Patent Document 1).

However, even in the invention according to the above proposal, it is difficult to manufacture a crystal having a predetermined carrier concentration distribution in a predetermined range with a high yield. The present inventors, using two or more kinds of B ₂ O ₃ of B ₂ O ₃ not doped with B ₂ O ₃ and Si oxides doped with previously Si oxide to improve the yield, these A method of controlling the carrier concentration distribution by stirring at an appropriate time has been proposed (see Patent Document 2). FIG. 6 shows the logarithmic value of (1-g) on the horizontal axis and the logarithmic value of the carrier concentration in the single crystal on the vertical axis, where g is the solidification rate of the Si-doped GaAs single crystal manufactured by the conventional manufacturing method according to this proposal. It is the figure which was taken. As shown in FIG. 6, the curve indicating the relationship between the carrier concentration and the solidification rate changes with a minimum value or a maximum value, and the carrier concentration distribution changes with a minimum value or a maximum value in the crystal growth direction. is doing. Such a distribution is extremely undesirable as a crystal.

Japanese Patent Publication No. 3-57079 Japanese Patent Application No. 9-96799

The present invention has been made under the above-mentioned background, and an object thereof is to provide a Si-doped GaAs single crystal having a good carrier concentration distribution.

As means for solving the above-mentioned problem, the first invention is a Si-doped GaAs single crystal produced by a vertical boat method using a liquid sealant , wherein the position in the single crystal is a crystal growth process. The horizontal axis represents the value of (1-g) on the horizontal axis, and the value of the carrier concentration in the single crystal at the position specified by each solidification rate g on the vertical axis. The vertical axis has the same scale, the horizontal axis has a range of (1-g) of 0.1 to 1.0, and the vertical axis has a carrier concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ . On the logarithmic graph taking a range, take the value of each carrier concentration at a position where the solidification rate g in the single crystal is specified in the range of 0.1 to 0.8, and then slope the line connecting the values When assuming that two straight lines with different
The two straight lines have a negative gradient with respect to the segregation coefficient of Si in GaAs when the solidification rate g is in the range of 0.1 to 0.8, and the straight line on the smaller solidification rate side. An Si-doped GaAs single crystal characterized in that the absolute value of the slope of is greater than 0.6, and the absolute value of the slope of the straight line on the higher solidification rate side is 0.6 or less. However, the gradient here is the value of a when the straight line is expressed as y = ax + b when the horizontal axis in the logarithmic graph is replaced with an orthogonal coordinate graph in which the horizontal axis is the x axis and the vertical axis is the y axis. .

A Si-doped GaAs single crystal according to the present invention is a Si-doped GaAs single crystal produced by a vertical boat method using a Si-doped GaAs single crystal liquid sealant, and the position in the single crystal is a crystal growth process. The logarithmic value of (1-g) is represented on the horizontal axis, and the logarithm of the carrier concentration in the single crystal at the position specified by each solidification rate is represented on the vertical axis. The curve is regarded as one or more straight lines or straight lines having a negative slope and an absolute value of the slope greater than 0.6 in the range of the solidification rate g of 0.1 to 0.8. And a curve that can be regarded as one or two or more straight lines or straight lines having an absolute value of the slope of 0.6 or less. Further, in the method for producing a Si-doped GaAs single crystal according to the present invention, in the crystal growth process, a reaction involving the movement of Si is performed between the liquid sealant layer and the GaAs raw material melt layer. In a state where the concentration of Si contained in the liquid sealant layer is high in the lower part near the interface between the liquid sealant layer and the GaAs raw material melt layer, and rapidly decreases as the distance from the interface increases to the upper part. Controlling the amount of Si taken into the liquid sealant by performing an operation of forcibly changing the Si concentration distribution of the liquid sealant layer in the crystal growth process, utilizing the phenomenon of having an equilibrium property. Thus, a Si-doped GaAs single crystal having a good carrier concentration distribution is obtained by controlling the Si concentration in the GaAs raw material melt layer. As a result, a Si-doped GaAs single crystal having a good carrier concentration distribution is obtained .

(Embodiment 1)
FIG. 1 is a log-log graph showing the carrier concentration distribution of a Si-doped GaAs single crystal according to the first embodiment of the present invention. FIGS. 2 to 4 are single logarithmic graphs used in the method for producing a Si-doped GaAs single crystal according to the present invention. It is explanatory drawing of a crystal manufacturing apparatus. Hereinafter, a Si-doped GaAs single crystal and a manufacturing method thereof according to Embodiment 1 of the present invention will be described with reference to these drawings.

The Si-doped GaAs single crystal according to this embodiment is manufactured by the vertical temperature gradient method in the vertical boat method. FIG. 2 is a cross-sectional view showing a schematic configuration of a single crystal manufacturing apparatus that performs the vertical temperature gradient method. In FIG. 2, reference numeral 4 denotes a crucible, and the raw material is accommodated in the crucible 4 and crystal growth is performed. The crucible 4 is substantially cylindrical and has an upper side opened and a lower side formed with a tapered cross section so that the diameter gradually decreases. The seed crystal 5 is accommodated in a small diameter portion at the lowermost end. It is like that.

  The crucible 4 is accommodated in a cylindrical crucible storage container 3 having a bottom, and the crucible storage container 3 is supported by the lower rod 1. The lower rod 1 can be moved up and down and rotated by a drive mechanism (not shown) so that the crucible storage container 3 and the crucible 4 stored in the crucible storage container 3 can be driven up and down and rotated. .

  The crucible storage container 3 is installed in a cylindrical heater 17. The heater 17 is composed of a plurality of heaters that can set the temperature independently, and can form a desired temperature gradient and temperature distribution in the crucible storage container 3. A cylindrical heat insulating material 16 is disposed outside the heater 17, and these are housed in an airtight container 11.

  A through hole that allows the lower rod 1 to pass therethrough is formed in the lower portion of the hermetic container 11, and a seal ring 11 a is fitted into the through hole, and the lower rod 1 can move up and down and rotate while maintaining the hermetic container 11 hermetic. It can be done. Further, a through hole is formed through the upper rod 12 in the upper portion, and a seal ring 11b is fitted into the through hole so that the upper rod 12 can move up and down and rotate while maintaining the hermetic container 11 airtight. It has become.

  The upper rod 12 can be moved up and down and rotated by a drive mechanism (not shown), and a stirring plate 10 is attached to the tip of the upper rod 12. The stirring plate 10 is a substantially rectangular plate body attached to a mounting portion at the tip of the upper rod 12 substantially vertically. The plate body of the stirring plate 10 has a horizontal width that is 1/2 or more of the inner diameter of the crucible 4 and a vertical width that is 1/2 or more of the thickness of the liquid sealant layer described later. Two or more plates may be provided. Furthermore, the stirring plate 10 may be of any shape in principle as long as it can stir the melt. Of course, the crucible 4 and the stirring plate 10 are made of a material having necessary heat resistance and hardly reacting with the raw material melt, such as carbon (C) or pBN.

The Si-doped GaAs single crystal is manufactured by the above-described single crystal manufacturing apparatus as follows. First, as shown in FIG. 4, the crucible 4 is filled with a seed crystal 5, a GaAs raw material 13, a Si raw material 14 as a dopant, and a B ₂ O ₃ raw material as a liquid sealant raw material.

Here, the amount of the raw material filled in the crucible 4 is as follows.
* GaAs raw material 13 ... 4000g
* Si raw material 14 as dopant: 0.02 to 0.03% by weight based on GaAs raw material
* As a liquid sealant material B ₂ O ₃ raw material (B ₂ O ₃ was added Si oxide to be 3% by weight Si equivalent concentration) ... 240 g

Next, the crucible 4 filled with these raw materials is set in the apparatus, and the raw materials are dissolved in accordance with the vertical temperature gradient method, and solidification is started. Solidification is performed from a portion in contact with the seed crystal 5 at the lower part of the crucible 4 where the temperature of the heater 17 is lowered, and gradually progresses upward. This solidification is also a process in which crystals grow from the seed crystal 5. The ratio of the weight of the solidified part to the weight of the entire GaAs raw material is called solidification rate g. The solidification rate g increases from 0 to 1 as the solidification progresses and the crystal grows. Therefore, the solidification rate g being a specific value means that the interface between the solidified portion and the melt portion is in a specific position corresponding to the value of g on a one-to-one basis. . The position specified by this is naturally the same even after the whole is solidified and the crystal is completed. Therefore, the position of the completed single crystal in the crystal growth direction can be specified by the solidification rate g.

In FIG. 2, the portion indicated by reference numeral 6 in the crucible 4 is a portion where GaAs is solidified, and the portion indicated by reference numeral 7 is a melt portion. The position of the interface between the solidified part 6 and the melt part 7 is a position represented by the solidification rate g at this time. A melted B ₂ O ₃ layer 8 as a liquid sealant is formed on the upper surface of the melt 7. In this embodiment, in the process of crystal growth, when the solidification rate g is 0.4, the upper rod 12 is moved downward as shown in FIG. _It is immersed in the ₂ O ₃ layer 8, the upper rod 12 is driven to rotate and the stirring plate 8 is rotated to stir the B ₂ O ₃ layer 8. This stirring is performed for 20 hours with the rotation speed of the stirring plate 8 set to 1 rpm.

When the carrier concentration distribution at each position of the Si-doped GaAs single crystal thus obtained was measured by the Vander Pauw method, the results shown in the log-log graph of FIG. 1 were obtained. In the graph of FIG. 1, the horizontal axis represents the position of the single crystal in terms of the solidification rate g of the crystal during the crystal growth process, and the logarithmic value of (1-g) is taken, and the vertical axis is specified by each solidification rate. This is a logarithmic value of the carrier concentration in the single crystal at the position to be measured. As shown in the graph of FIG. 1, the curve indicating the carrier concentration distribution is such that two straight lines having a negative gradient are connected at a solidification rate g of 0.4, and a smooth increasing tendency is obtained. Is shown. Moreover, the slope of the straight line when the solidification rate g is 0.1 to 0.4 is about -0.85, and the slope of the straight line when the solidification rate g is 0.4 to 0.8 is about -0.3. there were. This result can be said to have a sufficiently good carrier concentration distribution that has not been obtained in the past. Here, the gradient is the value of a when the straight line is expressed as y = ax + b in the orthogonal coordinates in which the horizontal axis in the graph is the x-axis and the vertical axis is the y-axis. This gradient has a certain correspondence with the segregation coefficient of Si in GaAs.

Obtaining such a good carrier concentration distribution is based on the discovery of a new fact that the present invention has not previously recognized. Hereinafter, this point will be described. In general, the carrier concentration distribution corresponds to the Si concentration distribution as a dopant. Further, for GaAs, the Si concentration, which is also an impurity, increases as the solidification rate g increases and does not become uniform. Accordingly, various attempts have been made to control the Si concentration distribution by utilizing the fact that the liquid sealant takes in Si. That is, the following reaction is performed between the B ₂ O ₃ melt layer, which is a liquid sealant in contact with the raw material melt, and the GaAs melt layer containing Si until the next reaction is in an equilibrium state.
3Si (in GaAs Melt) + 2B ₂ O ₃ = 3SiO ₂ (to B ₂ O ₃ ) + 4B (to GaAs Melt)

Therefore, by the B ₂ O ₃ layer into two layers, the lower layer of SiO ₂ in advance appropriate amounts in addition to the B ₂ O ₃ layer (GaAs layer side), left without added SiO ₂ in the upper layer. While the solidification rate g is small (the Si concentration is also small), Si taken in from the GaAs layer is decreased so that the lower layer in this state is in the equilibrium state. When the solidification rate g reaches a predetermined value (the Si concentration of the GaAs layer also increases), the upper layer and the lower layer are mixed to reduce the lower SiO ₂ concentration, and the Si incorporated into the B ₂ O ₃ layer from the GaAs layer To increase. This is intended to make the Si concentration distribution uniform (see Japanese Patent Application No. 9-96799 for details).

However, although it has been found that the Si concentration distribution can be made uniform to some extent by the above method, even if the amount of SiO ₂ added to the two layers of B ₂ O ₃ is variously changed, the theoretically assumed uniformity can be obtained. I couldn't. In particular, when an amount that should improve the uniformity is added based on trial and error results, the Si concentration distribution may show a discontinuous distribution as shown in FIG. I understood it.

The present invention is based on new facts discovered in the process of investigating this cause. That is, conventionally, it has been premised on common sense knowledge that the Si concentration in the melt is substantially uniform. In order to investigate the cause, the present inventors examined the Si concentration in the B ₂ O ₃ layer, which is a liquid sealant, and found that the B ₂ O ₃ layer had a lower portion near the interface with the GaAs melt layer. It was found that the Si concentration was high, and the Si concentration decreased rapidly as it moved away from the interface and moved upward.

  As a result of this fact, the reason why the conventional method of forming a liquid sealant in two layers does not necessarily achieve the effect as theoretically assumed, and at the same time, the present invention can be made. It is a thing.

(Embodiment 2)
Since this embodiment is the same as Example 1 except that the timing of stirring is performed from the time point when the solidification rate g is about 0.55, detailed description thereof is omitted.

FIG. 5 is a log-log graph showing the carrier concentration distribution at each position of the obtained Si-doped GaAs single crystal. The horizontal axis and vertical axis of the graph in FIG. 5 are the same as those in the first embodiment. As shown in the graph of FIG. 5, the curve indicating the carrier concentration distribution includes a first straight line having a solidification rate g of 0.1 to 0.55 and a solidification rate g of 0.55 to 0.8. Two straight lines having a negative gradient together with the second straight line in the range are connected to each other, indicating a smooth increasing tendency. Moreover, the slope of the straight line when the solidification rate g is 0.1 to 0.55 is about -0.85, and the slope of the straight line when the solidification rate g is 0.55 to 0.8 is about -0.3. there were. This result can be said to have a sufficiently good carrier concentration distribution that has not been obtained in the past.

(Comparative example)
In this comparative example, a B ₂ O ₃ layer (50 g) to which no Si oxide is added is arranged on the B ₂ O ₃ layer 8 in the first embodiment, so that two liquid sealant layers are provided. Other than that, the crystal growth was performed under the same conditions as in the first embodiment, including the stirring conditions. The carrier concentration distribution at each position of the obtained Si-doped GaAs single crystal was as shown in the log-log graph shown in FIG. As shown in FIG. 6, the curve indicating the relationship between the carrier concentration and the solidification rate is discontinuous, and the carrier concentration distribution changes discontinuously in the crystal growth direction. Such a distribution is extremely undesirable as a crystal.

  In each of the embodiments described above, the case where the timing and conditions of stirring are specific is shown. However, the present invention is not limited to this, and in the crystal growth process, the liquid sealant layer and the GaAs raw material melt A reaction involving the movement of Si is carried out between the layer and the reaction, and the concentration of Si contained in the liquid sealant layer is lower in the vicinity of the interface between the liquid sealant layer and the GaAs raw material melt layer. In the crystal growth process, the Si concentration distribution in the liquid sealant layer is forcibly changed by utilizing the phenomenon of having an equilibrium property in a state of being high and low and abruptly lowering as it goes away from this interface and moves upward. The amount of Si taken into the liquid sealant is controlled by performing an operation, thereby controlling the Si concentration in the GaAs raw material melt layer to obtain a Si-doped GaAs single crystal having a good carrier concentration distribution. Including the case of .

  That is, for example, the timing of stirring may be other than the timing shown in the above embodiment as long as the carrier concentration distribution of GaAs is within a predetermined range. The stirring conditions may be other than the conditions shown in the above embodiment as long as the carrier concentration distribution of GaAs is within a predetermined range. Therefore, in some cases, as long as the stirring conditions satisfying the above conditions can be selected, stirring may be continuously performed to constantly change the Si concentration distribution of the liquid sealant.

Further, the stirring may be performed by immersing and stirring the stirring plate 10 in the liquid sealant and rotating the lower rod 1. Of course, both the stirring plate 10 and the lower rod 1 may be rotated. Further, the Si concentration distribution of the liquid sealing agent layer may be forcibly changed by stirring the GaAs by immersing the stirring plate 10 in the GaAs melt without stirring the liquid sealing agent. .

  The present invention also relates to a Si-doped GaAs single crystal produced by a vertical boat method using a liquid sealant, wherein the position in the single crystal is represented by the crystal solidification rate g in the crystal growth process ( A curve represented by a graph in which the logarithmic value of 1-g) is taken on the horizontal axis and the logarithmic value of the carrier concentration in the single crystal at the position specified by each solidification rate is taken on the vertical axis is a solidification rate g of 0. In the range of 1 to 0.8, the gradient has a negative value, and the absolute value of the gradient is 0 or more, and the absolute value of the gradient is 0. It includes all Si-doped GaAs single crystals characterized in that one or two or more straight lines or straight lines of .6 or less are connected to an assumed curve.

  Moreover, although the case where the vertical temperature gradient method is used is shown in the embodiment, this may be a vertical Bridgman method.

It is a log-log graph which shows the carrier concentration distribution of the Si dope GaAs single crystal concerning Embodiment 1 of this invention. It is sectional drawing which shows schematic structure of the single-crystal manufacturing apparatus which enforces the vertical boat method used for the manufacturing method of the Si dope GaAs single crystal concerning this invention. It is explanatory drawing of the single crystal manufacturing apparatus used for the manufacturing method of the Si dope GaAs single crystal concerning this invention. It is explanatory drawing of the single crystal manufacturing apparatus used for the manufacturing method of the Si dope GaAs single crystal concerning this invention. It is a log-log graph which shows the carrier concentration distribution of the Si dope GaAs single crystal concerning Embodiment 2 of this invention. It is a log-log graph which shows carrier concentration distribution of the Si dope GaAs single crystal concerning a prior art example.

Explanation of symbols

1 ... lower rod 3 ... crucible container, 4 ... crucible, 5 ... seed crystal, 6 ... solidified portion, 7 ... molten portion, 8 ... liquid sealant serving B ₂ O ₃ layer, 10 ... stir plate, 11 DESCRIPTION OF SYMBOLS ... Airtight container, 12 ... Upper rod, 11a, 11b ... Seal ring, 16 ... Heat insulating material, 17 ... Heater.

Claims (1)

A Si-doped GaAs single crystal produced by a vertical boat method using a liquid sealant,
The position in the single crystal is represented by the solidification rate g of the crystal in the crystal growth process, the value of (1-g) is taken on the horizontal axis, and the value of the carrier concentration in the single crystal at the position specified by each solidification rate g The horizontal axis and the vertical axis have the same scale, the horizontal axis is in the range of (1-g) 0.1 to 1.0, and the vertical axis is 5 × 10 5 of the carrier concentration. ^{On the} log-log graph taking the range of ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , the value of each carrier concentration at the position where the solidification rate g in the single crystal is specified in the range of 0.1 to 0.8 is shown. When the line connecting the values is considered as two straight lines with different slopes connected ,
The two straight lines have a negative gradient with respect to the segregation coefficient of Si in GaAs when the solidification rate g is in the range of 0.1 to 0.8, and the straight line on the smaller solidification rate side. An Si-doped GaAs single crystal characterized in that the absolute value of the slope of is greater than 0.6, and the absolute value of the slope of the straight line on the higher solidification rate side is 0.6 or less .
However, the gradient here is the value of a when the straight line is expressed as y = ax + b when the horizontal axis in the logarithmic graph is replaced with an orthogonal coordinate graph in which the horizontal axis is the x axis and the vertical axis is the y axis. .

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