JPH0193497A - Production of znse single crystal - Google Patents

Abstract

PURPOSE:To obtain ZnSe single crystal with desired crystal orientation by preparing ZnSe polycrystal within which the ZnSe seed crystal is contained followed by zone annealing of said polycrystal in an inert atmosphere. CONSTITUTION:(1) A ZnSe polycrystal within which the ZnSe seed crystal is contained is prepared by the CVD or sintering process, and a rodlike ZnSe polycrystal 1 is processed so that the ZnSe seed crystal 4 is carried at one end and the desired crystal orientation of the objective single crystal in the longer direction and that of the seed crystal coincide; (2) the polycrystal 1 is moved with the seed crystal 4 in the lead in an inert gas or nitrogen gas atmosphere of 0.1-100Torr through the temperature zone consisting of (i) low- temperature portion AB of room temperature -100 deg.C, (ii) temperature-rising portion BC with the temperature gradient of 50-200 deg.C/cm, (iii) high-temperature portion CD of temperature T2 of 700-900 deg.C, (iv) temperature-falling portion DE with the temperature gradient of -200--50 deg.C/cm, and (v) low-temperature portion EF of room temperature -100 deg.C at a rate of 0.05-5mm/day. The ZnSe polycrystal is thus converted, while retraining solid phase, into the objective ZnSe single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical Field The present invention relates to a method for producing a bulk single crystal of ZnSe having a desired orientation.

ZnSe is a II-Vl group compound semiconductor. The bandgap is wide at 2.7 eV. Therefore, it is highly expected to be used as a material for blue LEDs.

Red, orange, yellow, green ty) L E D (Light E
Mitting Diode: Light emitting diode)
A practical manufacturing method has already been established. Used in large quantities.

However, blue LEDs have not yet reached a practical stage.

Since it emits blue light, the band gap is 2.5e.
A semiconductor with a voltage higher than V must be used.

Such materials include GaN, SiC, ZnSe,
ZnS.

GaAIN, ZnSSe, etc. are known.

Whichever material is used, a high quality single crystal must be obtained. Each of these materials has its own drawbacks, and a practical blue LED has not yet been produced.

ZnSe has a drawback in that high-quality single crystals with few impurities cannot be obtained.

Furthermore, although n-type ZnSe single crystals can be produced, p-type ZnSe single crystals have not been produced. If it is not possible to create a pn junction, an LED cannot be produced.

However, recently there has been a report that p-type ZnSe has been created by doping with Li.

J, NiN15hiza et al, J, Ap
pl, Phys, 576 p, 2210 Therefore,
ZnSe is expected to be a material for blue LEDs.

The reason why it is difficult to control the conductivity is that it is difficult to obtain a large bulk single crystal of ZnSeQ with high purity.

Since high-quality large bulk single crystals cannot be obtained, GaAs,
A Znse thin film single crystal is heteroepitaxially grown on a substrate such as Go.

Molecular beam epitaxy (
MBE), metal organic pyrolysis (MOCVD or OMV)
PE) etc. can be used.

In this way, a thin film single crystal of ZnSe can be produced.

However, since it is heteroepitaxy, there are the following two drawbacks. One is that dislocations are likely to occur due to lattice mismatch. Another problem is that when the substrate is heated, elements contained in the substrate diffuse into the thin ZnSe layer. There are problems with dislocation and impurity diffusion,
ZnSe thin films made by heteroepitaxy are not of good quality and cannot be made p-type.

In order to solve such problems, large bulk ZnS
e It is preferable to make a single-crystal wood board and homoepitaxially coat the ZnSe thin film on it.

However, it is extremely difficult to produce large, highly pure ZnSe bulk single crystals.

(a) Conventional technology n-vi group compound semiconductors ZnS, ZnSe, ZnT
e cy) What makes it difficult to make single crystals is that they do not melt unless high pressure is applied. It is a substance that sublimates easily. Even if it is heated without applying pressure, it will simply sublimate. It does not melt even when heated.

There was a time when it was thought that these materials could not melt.

To melt ZnSe, an inert gas pressure of 50-'80 atm must be applied and heating to a high temperature of 1520° C. or higher is required.

In the case of m-v group compound semiconductors, L E C (Liqu
idEncapsulated Czochralsk
i) The law is valid. The single crystal is pulled up while covering the melt with a thick layer of B2O3 and applying inert gas pressure.

However, in the case of ■-■ group compound semiconductors, the LEG method cannot be used. This is because the raw material reacts with B2O3.

For these reasons, ZnSe single crystals cannot be produced using normal crystal growth methods.

High-pressure melting method (high-pressure Bridgman method, high-pressure Tamman method),
Attempts have been made to grow Zn5a single crystals using iodine transport method, sublimation method, etc.

However, products made using the first two methods may generate twins or be contaminated by impurities.

Large single crystals cannot be obtained using the sublimation method.

Several other single crystal growth methods have also been attempted.

In either method, the electrical properties, crystallinity, purity, crystal shape, size, etc. of the resulting crystals were not satisfactory.

(1) Zone annealing method Applicants made polycrystals of ZnSe and heated them with Ar
We have developed a method for single crystallization by annealing through a narrow hot zone and a sharp temperature gradient in an atmosphere such as gas (Japanese Patent Application No. 62-65389, S62.
3.18 application).

ZnSe single crystals are not directly made from powdered materials. Polycrystals of ZnSe are made by a CVD method or a sintering method. This is processed into a rod shape and subjected to zone annealing to form a single crystal.

Zone annealing techniques are well known. However, this was used to improve the crystallinity of single crystals.

The above-mentioned invention revealed for the first time that polycrystalline ZnSe can be made into a single crystal by zone annealing.

This method does not involve once sublimating a sintered body to form a single crystal, as in the sublimation method. While maintaining the solid phase, annealing is performed by locally heating (hot zone) and gradually moving the heated area.

The pressure is low (0.1-100 Torr) and the temperature is low (700-9000C).

ZnSe polycrystals can be made into single crystals at low temperatures and low pressures.

In the high-pressure Bridgman method, which uses high temperature and high pressure, C, S
It is easy for impurities such as i to enter, and dislocations are also likely to occur due to thermal strain.

However, the zone annealing method described above has THM (T
ravelling Heater Method)
By using this method and annealing at low temperature and low pressure, products with few impurities and few dislocations can be obtained.

2) Problems to be solved by the invention What kind of crystal orientation can a single crystal be produced using the zone annealing method described above? It is impossible to know this in advance.

In the hot zone, a heated crystal grain acts as a nucleus and acts on adjacent crystal grains, changing their crystal orientation to become the same as itself. The area where the crystals and orientations are the same gradually increases.

In this case, the crystal orientation of the nucleus that forms the basis of single crystallization is determined by chance. In other words, single crystallization occurs in various crystal orientation directions.

This is an inconvenience.

The required wafer orientation is, for example, the (100) plane or the (1
11) It is fixed, such as the surface.

It would be advantageous if a single crystal ingot with an orientation suitable for cutting out a wafer with such an orientation could be obtained.

00 Purpose It is an object of the present invention to provide a method for producing a ZnSe single crystal having a desired crystal orientation from a ZnSe polycrystal by a zone annealing method.

(9) Method of the present invention In the method of the present invention, the polycrystal for zone annealing partially contains a seed crystal having a desired crystal orientation, and zone annealing is performed from the vicinity of the seed crystal.

Polycrystals are manufactured by CVD or sintering.

The CVD method and the sintering method are well-known methods. In the present invention, polycrystalline ZnSe containing a single crystal inside is produced by these methods.

The CVD method is performed as follows. A single crystal with a desired orientation is placed in a CVD furnace. In this state, raw material gas is sent to grow ZnSe polycrystals on the heated substrate.

In this way, a polycrystal containing a single crystal inside is formed.

After the polycrystal growth is completed, ZnSe is cut into a suitable rod shape. At this time, the first single crystal placed is cut out so that it is located at the end of the bar in the desired direction.

This single crystal determines the direction of single crystallization during zone annealing. Therefore, this single crystal will be called a seed crystal.

A method for producing ZnSe polycrystals using the CVD method will be explained with reference to FIG.

In the CVD method, Zn vapor is reacted with H, Se gas,
By the following reaction, H2SeCl1) + Zn(v) w ZnSe(s)
+H2(1)ZnSe is obtained and deposited onto the substrate.

Although there are various CVD methods, here, a method in which a zinc evaporation furnace and a reactor are housed in one container is shown.

A heater 12 is provided around the outer periphery of the zinc evaporation furnace 11, and the zinc contained in the zinc container 13 is converted into molten zinc 14. The molten zinc 14 is further heated to produce zinc vapor.

Ar gas is introduced here. Zn vapor is transported toward the reactor 15 by Ar gas.

Furthermore, H2Se is fed toward the reactor as a raw material gas.

In the reactor 15, a substrate 17 is provided in a reaction vessel 19. The substrate 17 is a horizontally long cylindrical body.

For example, it has a square cylindrical shape. A heater 16 is provided outside the reaction container 19 so as to surround the substrate 17.

The heater 16 heats the substrate 17 to a temperature higher than the crystallization temperature. The chemical reaction described above takes place in the region above the crystallization temperature.

The reaction product, ZnSe, is deposited on the substrate.

Unreacted gas, hydrogen gas, and Ar gas are exhausted.

In order to carry out the method of the present invention, a seed crystal 4 is placed on the substrate 17 in advance.

The seed crystal 4 may be small. One or more may be placed on the substrate 17. If you use a large board,
Since large polycrystals of irregular shape can be obtained, it is possible to cut out a number of rods to serve as samples for zone annealing used in the present invention.

Since the ZnSe polycrystal is formed on the substrate 17, the larger the substrate 1γ, the larger the ZnSe polycrystal. However, since it is irregular in shape, it cannot be used as is; it must be cut into an appropriate shape.

The length of the board is about 1 m, and in the case of a square tube, it is several tens of cm.
Often a corner. By depositing on such a wide substrate, thin but large dimensions are obtained. Since you are cutting this, you can cut things in any direction or shape.

Since there is a seed crystal 4, it is processed into a rod shape including the seed crystal 4 and having the desired crystal direction as the longitudinal direction. This is the starting material.

Such seeded polycrystals can also be made by sintering. In this case, seed crystals and powder raw materials are placed in a hot press, heated to 600°C to 900°C, and heated to 200 to 300°C.
Pressure mold into ATM.

In this way, a ZnSe polycrystal having a seed crystal at one end is obtained. FIG. 3 shows a ZnSe polycrystalline processed into a round bar and a ZnSe polycrystalline processed into a square bar.

The zone melting method of the present invention will be explained with reference to FIG.

A ZnSe polycrystal 1 is sealed inside a quartz capsule 2. The inside of capsule 2 has a pressure of 0.1 to 10 Q Tor.
The atmosphere is Ar, Ne, He, or N2. Any gas may be used as long as it is inert and does not react with ZnSe.

The role of the atmosphere is to suppress sublimation of the raw material from the surface of ZnSe. Since the temperature is not high (for example, 1600° C.), the pressure of the atmosphere may be low.

The quartz capsule may be an open tube. In this case, the atmospheric gas whose pressure is adjusted to 0.1 to IQ □ Torr is passed through the open tube.

The quartz capsule may be omitted altogether. The entire device is installed in a vacuum device, and the atmosphere of the vacuum device is set at 0.1 to 100 Torr.
It may be used as an inert gas.

A suspension device 3 suspends the quartz capsule from above.

A ring-shaped heater 5 with a narrow vertical width is provided.

ZnSe polycrystal 1 gradually passes through heater 5. Approach the heater 5 from one end of the seed crystal 4 and pass it through the heater 5.

This heater 5 is a highly localized heater that can heat only a very narrow area. The temperature distribution is shown on the side of Figure 1.

The temperature is at room temperature T1 at AB and EF, which are far from the heater 5.
High temperature area T of 700°C to 900°C near the heater 5 CD
It becomes 2. In the high temperature zone T, a movement from polycrystalline to single crystallization occurs.

Single crystallization occurs continuously from the portion passing through the heater 5. The width CD of the high temperature section T should be as narrow as possible. This depends on the geometry of the heater, but 7
High temperature zone CD defined as 00-900℃ is 5-20
It must be about mm.

When the width CD is wide, the movement toward the single crystal occurs at distant points within the width CD, which tends to cause twin crystals. Therefore, it is required that the width CD be narrow.

In addition, the temperature gradient BC before and after the high temperature part, Dli: 50
The ZnSe polycrystal 1 moves longitudinally through such a temperature distribution, which must have a steep slope of ~±200°C/cm. Heat the seed crystal first. The portion that contacts the seed crystal is single crystallized to have the same crystal orientation as the seed crystal.

As the hot zone (high temperature area) moves through the polycrystal, it becomes a single crystal one after another so that it matches the part that was just previously made into a single crystal.

Movement speed (annealing speed) is 0.05mm to 5+t+m
/ day.

When annealed to the opposite end, the whole becomes a single crystal with the same crystal orientation as the seed crystal.

In the present invention, ZnSe is hardly sublimed even in the high temperature part CD. It undergoes a phase transition from polycrystal to single crystal while maintaining the solid phase without sublimation.

This does not mean that no sublimation occurs in the present invention. However, it does not actively use sublimation like the sublimation method.

In the present invention, heating is performed in an inert gas atmosphere to prevent sublimation as much as possible.

(→Example 5 mmX 5 mrnX 3 mm rectangular parallelepiped ZnSe
A single crystal was placed in advance on a substrate of a CVD device, and a ZnSe polycrystal was produced by the CVD method. This single crystal is 5X5
The normal line erected to the mm plane is equal to the (110) direction.

5mm x 5InI11x including a single crystal at one end
A 50m1II ZnSe splint-shaped polycrystal was cut.

Put this into a quartz capsule and apply Ar gas I Torr.
Annealing was carried out in this atmosphere. The temperature T2 of the high temperature part is 86
The temperature T of the low temperature part was set to 0° C. and room temperature. The temperature gradients of BC and DE were set to +100°C/cm and -1008C/cm. The vertical movement speed of the quartz capsule was set at 2 mm/
After annealing, the ZnSe sample was taken out by breaking the quartz capsule.

The crystallinity of the ZnSe samples was investigated by interfold and X-ray diffraction. As a result, it was found that the crystal was a single crystal in which the longitudinal force was in the 8' (110) direction. This means that the crystal orientation is determined by the seed crystal.

(b) Effects (1) Since a polycrystal with a seed crystal is single-crystallized as a starting material, a ZnSe single-crystal ingot with a desired orientation can be produced.

(2) A relatively large Zn5a single crystal can be manufactured.

(3) High purity ZnSe single crystals with few residual impurities can be produced.

This is because unlike the solution method and iodine transport method, no solvent or transport agent is used. Also, like the high-pressure Bridgman method,
This is because conditions such as high temperature and high pressure, where impurities easily enter, are not required.

Further, sublimable donor impurities are removed by zone annealing.

(4) Since high temperature and high pressure are not used as in the high-pressure Bridgman method, a single crystal with few dislocations can be obtained.

(5) It is a reproducible method.

(6) It can be used as a substrate for blue LEDs.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the operation of zone annealing according to the present invention. FIG. 2 is a longitudinal cross-sectional view of an apparatus for producing ZnSe polycrystals by the CVD method. FIG. 3 is a perspective view of a ZnSe polycrystal made by the CVD method and processed into a bar material. 1... ZnSe polycrystal 2... Quartz capsule 3... Suspension device 4... Seed crystal

Claims (1)

[Claims] A ZnSe polycrystal containing a ZnSe seed crystal inside is made by a CVD method or a sintering method, and the required crystal orientation in the longitudinal direction of the single crystal with the ZnSe seed crystal at one end matches the crystal orientation of the seed crystal. A rod-shaped ZnSe polycrystal is processed, and in an inert gas or nitrogen gas atmosphere of 0.1 Torr to 100 Torr, a low temperature part AB of room temperature to 100°C and a temperature gradient of 500°C/cm to 200°C/cm are processed. A certain temperature rising part BC, a high temperature part CD whose temperature T_2 is 700°C to 900°C, and a temperature gradient of -200°C/cm to -50°C/cm.
0.05mm/day to 5mm within the temperature gradient consisting of the temperature decreasing part DE which is
A method for producing a ZnSe single crystal, characterized in that ZnSe polycrystal is changed into a ZnSe single crystal while maintaining a solid phase by moving the seed crystal first at a speed of /day.