JPH04114991A - Method for growing crystal - Google Patents

Abstract

PURPOSE:To grow a mixed crystal having an arbitrary composition on a seed crystal by bringing a melt consisting of three or more components into contact with a seed crystal consisting of one or more component, lowering the temperature and feeding a source material to the resultant mixed crystal. CONSTITUTION:A crucible 4 housing a melt 6 consisting of three or more components therein is arranged on a housing chamber 8 in which a source material is housed. Then the material 9 is used as either one electrode and alternating current or direct current is sent between the above-mentioned electrode and electrode 7 brought into contact with the surface of the melt 6 and the melt 6 on the circumference of the material 9 is heated and then solid-liquid interface temperature of seed crystal 1 mounted in crystal-pulling up device arranged in the center of the surface of the melt 6 and the melt 6 is lowered to grow a mixed crystal layer 2 having a composition gradient on the seed crystal 1 and then the source material 9 is fed while keeping the solid-liquid interface temperature constant to grow a mixed crystal 3 having a specific composition on the crystal 2.

Description

Detailed Description of the Invention U Overview The present invention relates to crystal growth of a mixed crystal having a composition of a mixture of two or more substances, using a mono- or binary crystal as a seed crystal and growing a mixed crystal having a desired composition. The purpose of the present invention is to provide a crystal growth method for growing crystals, in which a seed crystal of one element or more is brought into contact with a melt of three or more elements,
A step of growing a mixed crystal layer with a composition gradient on the seed crystal by lowering the temperature of the solid-liquid interface, and replenishing the insufficient source material while keeping the temperature of the solid-liquid interface constant. and growing a mixed crystal of a constant composition on the composition gradient layer.

[Industrial Field of Application] The present invention relates to crystal growth, and in particular to the crystal growth of mixed crystals having a composition of a mixture of two or more substances.

Crystals of pure elements or compounds each have unique electrical properties, optical properties, etc. From the viewpoint of designing electrical devices and optical devices, it is sometimes desirable to have properties intermediate between crystals of two or more pure substances, rather than crystals of these pure substances.

Mixed crystals of two or more substances are an attempt to meet these demands.

In optical semiconductor devices and high-speed semiconductor devices, compound semiconductor mixed crystals are often desired.

[Prior art] GaAs, InP, which is a compound of group III elements and group V elements
N-V group compound semiconductors such as N-V compound semiconductors are excellent semiconductor materials, and mixed crystals can be made with almost any composition.

However, commonly available crystal substrates are GaAs,
It is a crystal of a pure compound such as InP, and it is extremely difficult to grow a crystal with a significantly different lattice constant on top of it.

In order to expand the range of applications of mixed crystal semiconductors, it is necessary to develop substrates with freely controlled lattice constants.

To this end, a technique for growing mixed crystal bulk crystals with a uniform composition of three or more elements is desired.The lattice constant of such a mixed crystal is generally different from that of a pure compound; Compound semiconductor substrates are insufficient. Therefore, mixed bulk crystals are desired.

One technique for growing a mixed bulk crystal is to grow a mixed crystal with a slightly different lattice constant on top of a compound semiconductor crystal, which is a pure substance, and then cut a new seed crystal from the grown mixed crystal. put out. A mixed crystal with a slightly different lattice constant is grown on the cut seed crystal, and a seed crystal is cut out from the grown mixed crystal again.

By repeating this procedure, any mixed bulk crystal can be grown.

Further, if the lattice constant of the mixed crystal to be grown is close to that of the pure compound crystal, the mixed crystal of the desired composition may be grown directly on the compound crystal.

[Problem to be solved by the invention] According to the conventional technology explained above, only a mixed crystal of a limited composition can be grown on a compound crystal of a pure substance, and it is difficult to grow a mixed crystal of an arbitrary composition. Therefore, many steps had to be repeated.

An object of the present invention is to provide a crystal growth method for growing a mixed crystal having a desired composition using a crystal of a pure substance as a seed crystal.

“Means to solve problems” FIGS. 1A and 1B are explanatory diagrams of the principle of the present invention.

In FIG. 1(A), a mixed crystal 2 having a composition gradient is grown on a seed crystal 1, and then a mixed crystal 3 having a constant composition is grown. As shown in the phase diagram of FIG. 1(B), a melt having a constant composition x0 is prepared, and the temperature is lowered from T1 to T2 at which solidification begins, so that the composition X1
A composition gradient mixed crystal whose composition changes from X2 to X2 is grown. Composition X. is selected so that the composition x1 of the mixed crystal to be solidified is close to that of the terminal substance (x=1) within a predetermined range. The final temperature T2 is selected so that the composition X2 of the obtained solid phase is close to the desired composition within a predetermined range.6 Next, as shown in Figure 1 (C), a composition gradient mixed crystal was brought into contact with the melt. In this state, the temperature of the solid-liquid interface, which is the interface between the solid phase and the liquid phase, is maintained at a nearly constant temperature T2, and the crystal is grown while replenishing the missing source material, thereby growing a mixed crystal with a constant composition. let Source material has composition X2
The composition does not necessarily have to be X2 as long as it promotes the precipitation of.

[Operation] By growing the compositionally gradient mixed crystal 2 on the seed crystal 1 of a pure substance, a crystal whose lattice constant is gradually changed can be obtained. A surface of any composition can be obtained by continuing growth until the desired composition is obtained.

Note that by making the composition gradient within the composition gradient mixed crystal 2 gentle, it is possible to obtain a mixed crystal surface that can be used as a seed crystal. After obtaining a surface with a desired lattice constant, by growing a mixed crystal 3 with a constant composition, a mixed crystal 3 with an arbitrary composition can be grown on the seed crystal 1 of a pure substance. Ru.

[Example] The phase diagram of a mixed crystal system will be explained with reference to FIG.

It is assumed that a compound BC and a compound AC, which continuously form a mixed crystal (A, B, and C represent elements), have a phase diagram as shown in FIG. Compound ThBC and compound AC are pure substances, and this phase diagram can be regarded as a quasi-binary system. In the phase diagram,
The horizontal axis represents the composition x (X of AB1-XC), and the vertical axis represents the temperature.

The curve p1 shown on the upper side of 5 in the figure shows a liquidus curve, and the lower curve p2 shows a solidus curve. That is, liquidus curve +
The region above 21 is entirely liquid (liquid phase), and the region below solidus curve p2 is entirely solid phase. In the region between these two curves Ω1 and ρ2, a solid phase and a liquid phase coexist.

Assume that a melt of composition X19 is created and the temperature is gradually lowered. When the temperature reaches T1, extend T1 horizontally to the right, and the composition x1s at the point where it intersects with the solidus curve 112
Since the solid phase composition XIS at which the solid phase begins to precipitate has a higher X value than the melt composition X112, the composition of the remaining melt gradually becomes lower in X. As the composition of the melt changes, the composition of the solid phase that solidifies gradually changes to one with a lower X value. In this way, when the temperature is lowered to T2, the composition of the same phase precipitated changes from xls to X2S. At this time, the composition of the melt changes from X1ρ to X2ρ.

In other words, if you want to obtain a composition gradient crystal whose composition gradually changes by using a mixed crystal melt and lowering the temperature, for example, if you want to obtain a crystal with a composition x2s, solidify. When the crystal composition reaches X2S, the melt no longer has the ability to grow x2s crystals. That is,
If the temperature is further lowered and growth continues, the composition will change further.

If the temperature is maintained at T2, the composition is fixed at X2S, or crystal growth does not occur because the melt has no remaining power to grow crystals. However, crystal growth is possible if new source material is supplied.

After growing a compositionally gradient crystal as described above, in order to grow a mixed crystal with a constant composition at the composition reached, it is necessary to replenish the insufficient source material. To explain with reference to the phase diagram in Fig. 2, if a material having an intermediate composition between the composition x211 of the melt and the terminal substance AC of the pure substance is supplied into the melt, the temperature is maintained at a constant temperature. At the solid-liquid interface, it is possible to grow a crystal having a composition x2s. By replenishing the source material having the composition x2s, the composition of the melt can be kept constant thereafter.

Methods for replenishing such source materials include adding solid source material to the melt, keeping the solid source material in constant contact with the melt, and making some parts of the melt hotter than other parts. There are other methods, such as bringing the source material into contact with the hot part.

FIG. 3 shows one configuration for replenishing source material.

In FIG. 3, a crucible 4 contains a melt 6 therein. Further, a storage chamber 8 is formed at the bottom of the crucible, and a liquid sealing material 5 is disposed as necessary on the surface of the melt 6 in which the source material 9 is stored.

In the case shown in Figure 4, a crystal pulling device is placed at the center of the surface of the melt 6, and a composition gradient mixed crystal 2 is grown on the seed crystal 1, and a constant composition mixed crystal 3 is further grown on top of the seed crystal 1.
This is a state in which the constant composition mixed crystal 3 has been grown halfway.

The surface of this mixed crystal 3 forms a solid-liquid interface, and its temperature T
or the crystal growth temperature. Note that an electrode 7 is arranged so as to surround the crystal pulling device, and this electrode 7 is at least partially buried in the melt 6.

When the source material 9 is a conductive substance, the source material 9 is used as one electrode, and the electrode 7 in contact with the melt surface is used as the other @ electrode, and an alternating current or direct current is passed between them. When a current is applied, heat is generated due to the current flowing through the resistance associated with the source material 9, heating the melt 6 around the source material 9. As the temperature of the melt 6 increases, the solubility of the source material 9 increases, and the source material 9 is added to the melt 6.
dissolves. If the resistance of the melt cannot be ignored, heat will also be generated due to the current distribution in the melt. By stopping the current supply, the heat generation caused by the current stops, and the source material 9
Also stops dissolving.

When a direct current is passed through the melt 6 using the electrode 7 as an anode and the source material 9 as a cathode, in addition to heating by Joule heat, the dissolved source material atoms are heated to the anode by the movement of electrons from the cathode 9 to the anode 7. direction, facilitating source material transport.

That is, in the case of heating by alternating current, the transport of the source material in the melt 6 is only by diffusion, or by direct current,
In addition to diffusion, acceleration by current can also be used.6 To explain with reference to Figure 2, the temperature is lowered from T1 to T2, and the composition is within a predetermined range from pure AC.
After growing a mixed crystal with a composition gradient varying from is to x2s, the temperature of the solid-liquid interface is maintained at T2, and the crystal is grown while being supplied with, for example, compound AC using a current-carrying device as shown in Figure 3. By continuing, it is possible to grow a desired constant composition mixed crystal 3 having the same composition X2S. At this time, even if the composition of the melt changes by replenishing the source material, it only changes the amount of melt that can be crystallized; unless the temperature at the solid-liquid interface changes, the composition of the growing crystal will change. It does not change. If a temperature gradient etc. is formed in the melt,
The amount of solid phase precipitated at the solid-liquid interface can be increased.6 FIG. 4 is a diagram schematically showing a mixed crystal grown on a seed crystal in this manner. On the seed crystal 1 of compound AC, a composition gradient mixed crystal AXB1-xC varying from X or Xl to x2 is grown, and on its surface is a constant composition mixed bulk crystal 3 of AyBlyC having a constant composition y. is growing.

By cutting out the grown constant composition mixed crystal 3, a mixed crystal substrate having a desired lattice constant can be obtained.

By growing the crystal as described above, it is possible to continuously grow a mixed crystal bulk crystal without having to cut out a seed crystal many times and grow the crystal thereon as in the conventional method.

Hereinafter, more specific examples will be described by taking a -V group semiconductor mixed crystal as an example.

[Growth of 1n0.12Ga0.88^S mixed bulk crystal] Ino, 12GaO, uAs is a crystal with a bandgap wavelength of approximately 098 μm, and is an optical material suitable for a bombing light source of a laser light source used for optical communication in the 1 μm band. It is a crystal.

First, a GaAs seed crystal with (111) 8 faces is prepared, a composition gradient crystal is grown on it, and then a desired In, 12
``Grow a 0.8sAs mixed crystal.GaAs was used as the source material placed in the crucible.The composition of the melt to be prepared first is such that a mixed crystal with a lattice constant sufficiently close to that of GaAs is grown. For example, on a phase diagram with 1nAs and GaAs as terminal materials, where X08 = 0°3890 x 1n-0, 1110 The temperature above the liquidus line (rho in Figure 2) is about 1200°C. That is, - a melt with this composition is heated to 1200°C or higher to form it, and the temperature is lowered to about 1200°C.
When the temperature drops to 00°C, solidification begins.

Using a crystal growth apparatus as shown in FIG. 3, the temperature of the melt was lowered using a melt having the above-mentioned composition, and crystal growth was started from 1200°C. The seed crystal is GaAs (11,1
,) 8 pages. Incidentally, crystal growth was performed by rotating the seed crystal at 20 rpm and pulling it at a speed of 2 mm/h+-. A B2O3 melt was formed on the melt, the surface of the melt was protected, and an external pressure of 9 atm was applied to prevent the evaporation of As.The temperature at the solid-liquid interface was increased from 1200℃ to 110℃
A composition gradient crystal was grown on the seed crystal by slow cooling to 0°C. When the solid-liquid interface temperature does not reach 1100'C, the temperature drop is stopped to maintain the solid-liquid interface temperature at a constant temperature, and electricity is applied to the GaAs source material provided in the crucible to generate heat, causing the GaAs to melt around it. Because it does not dissolve in the liquid,
The source material was transported to the solid-liquid interface by diffusion, etc., and growth was performed. Approximately 10 hours after maintaining a constant temperature, 2
Mixed bulk crystal growth was performed at a pulling rate of mm/hr. When this crystal was collected and analyzed,
The composition of the composition gradient mixed crystal is InGaA
Change from s to In, -, 2Gao, 8sAs is 0.
025 0.975. In addition, the bulk of the mixed crystal with a constant composition grown on the composition gradient mixed crystal is ■no, 12GaO, 88'''
It had a uniform composition of about 20 mm and a thickness of about 20 mm. This crystal with a certain composition was a single crystal and was of high quality enough to be used as a substrate for electronic devices.

FIG. 5 shows an example of the composition change in the thickness direction of the grown composition gradient mixed crystal. Growth is In G
a As's thread and formation to woman ii Mari, In0.12G
The composition ended up being close to aO, 880,050,95 As. Note that the measurement was performed using XMA.

Note that the composition gradient mixed crystal JnxGa1-x in the above case
As grew on the GaAS crystal at x=0.025 and was changed to x=0.12 at a thickness of about 25 mm. The crystallinity of the composition gradient mixed crystal was single crystal, and almost no cracks were generated. For lattice matching with the seed crystal, the lattice mismatch is approximately 0.35%, X≦0.
It is desirable to start the growth at ,05. At this time again,
If the growth is started at x=O, a compositionally gradient mixed crystal can be grown.If the value of X is small, the thickness of the compositionally gradient mixed crystal must be increased, so it is recommended to set Preferably, the X value at the start of growth of the composition gradient mixed crystal grown on the GaAs seed crystal is 0.01≦X
It is desirable that it be in the range of ≦0.05.

Although the growth of a mixed crystal using 1nAs and GaAs as quasi-binary materials will be described, other mixed crystals can be grown using the same procedure. An example will be described below.

Using GaP as a seed crystal, the melt is made of GaAs and GaP quasi-2.
XPl-X is grown on ternary mixed crystal Ga using GaP as the source material.

The seed crystal is GaP, the melt is a quasi-binary system of GaP and InP, and ternary mixed crystals Ga, In1-, and P are grown while supplying GaP as a source material.

The seed crystal is InP, the melt is a quasi-binary system of InAs and InP, and InP is supplied as a source material to grow a ternary mixed crystal 1nAs, p 1-.

The seed crystal is GaP, GaAs, or InP, the melt is a quaternary system of InAs, GaAs, GaP, and 1nP, and the source material is L″′CGaP-* or GaAs,
or lnP, more preferably both or a mixture thereof, to form a quaternary mixed crystal 1n1- xGa xAsl-
, p , grows.

The seed crystal is GaSb, the melt is a quasi-binary system of InSb-GaSb, and GaSb is replenished as a source material.
One that grows the elemental mixed crystal In, -XGa, XSb.

Using GaAs as a seed crystal, using the melt as a quasi-binary system of GaAs-Garb, and supplying GaAs as a source material, a ternary mixed crystal, GaAS xSbl-, is grown.

The seed crystal is InAS, the melt is a quasi-binary system of InAs and 1nSb, nAs is supplied as a source material, and a ternary mixed crystal 1nAs X5b1-x''k is grown.

The seed crystal is GaAS, 1nAs, or GaSb, and the melt is InAS, InSb, GaAs, or GaS.
A quaternary mixed crystal 1n1-xGaxAsl-vSb is formed by adding GaAs, 1nAs, GaSb, or a mixture thereof as a source material
The 6 seed crystals to be grown are GaAs, and the melt is A.
A quasi-ternary system of 18S, GaAs, and InGaAs,
By supplying AlAs, GaAs, or a mixture thereof as a source material, quaternary mixed crystal AI Ga J
n Something that grows As.

x y 1-x-y The seed crystal is GaP, the melt is a quasi-ternary system of 81P, GaP, and InP, AIP, GaP, or a mixture thereof is supplied as a source material, and the quaternary mixed crystal A4 is xGa
, In1-x-those that grow.

The seed crystal is GaP, and the melt is A' l S b and GaS
A quasi-ternary system of b and TnSb is used as the source material, and AlS
b, or GaSb, or a mixture thereof;
One that grows quaternary mixed crystal AI Ga Jn Sb.

X y 1-x-y Note that the same method can be used to grow not only the above-mentioned ■-V group semiconductors but also II-Vl group semiconductors, various other semiconductors, and mixed crystals of metals and dielectric crystals. Can be used.

Note that when using a metal or dielectric source, a heater can also be used to heat the source.

Although the present invention has been described above with reference to examples, the present invention is not limited to these examples. For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

Effects of the Invention As described above, according to the present invention, a mixed crystal having an arbitrary composition can be created on a crystal of a pure substance as a seed crystal.

A desired mixed crystal can be easily obtained through a simple process.

[Brief explanation of the drawing]

FIGS. 1(A) to 1(C) are diagrams explaining the principle of the present invention,
Figure 1 (A is a schematic diagram showing the structure, Figure 1 (B) is a phase diagram to explain the growth of a composition gradient layer, and Figure 1 (C) is a diagram to explain the growth of a mixed crystal with a constant composition. FIG. 2 is an enlarged phase diagram of a mixed crystal system, FIG. 3 is a schematic sectional view of a crystal growth apparatus, and FIG. 4 is a schematic sectional view of a grown crystal. Fig. 5 is a graph showing the change in composition with respect to the thickness within the grown composition gradient mixed crystal layer. Seed crystal composition gradient mixed crystal crystal constant composition mixed crystal crucible liquid sealing material melt electrode (anode) accommodation Chamber sauce materials Figure 3 Figure 4

Claims (5)

[Claims] (1) A mixed crystal layer with a compositional gradient is grown on the seed crystal by bringing a single or more elemental seed crystal into contact with a ternary or more elemental melt and lowering the temperature at the solid-liquid interface. and growing a mixed crystal of a constant composition on the composition gradient layer by replenishing insufficient source material while keeping the temperature of the solid-liquid interface constant. (2) The crystal growth method according to claim 1, wherein the initial composition of the composition gradient crystal grown on the seed crystal is approximately equal to the composition of the seed crystal. (3) The crystal growth method according to claim 1 or 2, wherein the insufficient source material is replenished by placing the source material in contact with the melt and passing a current through the source material. Crystal growth method. (4) The crystal growth method according to claim 3, wherein the temperature of the source material is set higher than the temperature of the solid-liquid interface. (5) The crystal growth method according to claim 3 or 4, wherein an anode is disposed in contact with the melt near the solid-liquid interface, and the source material serves as the cathode.