CN102352527A - Method for growing zinc oxide crystals through induction heating and pressure - Google Patents

Abstract

The invention discloses a method for growing zinc oxide crystals through induction heating and pressure, which adopts a induction heating and pressure crystal growing device and comprises the following steps: heating a zinc oxide raw material in a crucible to melt, and slowly cooling to lead the melt to gradually crystallize along the seed crystals and ensure crystal growth is completed. By adjusting an induction coil and a heat insulating material, the temperature field gradient of the device can be adjusted to 20-80 DEG C/cm. The temperature is adjusted in a cooling rate of 1-20 DEG C/h in the crystal growing process, the temperature is adjusted in a cooling rate of 20-100 DEG C/h after crystal growth, and the crystals are cooled to the room temperature along with the furnace after a power supply is powered off. The method has the advantages that the temperature field and crystal growth interface are stable, the growth pressure is low (less than 4MPa), the growth period is short, the crystal purity is high, and the growing device is simple and is convenient and easy to control; ZnO crystals with high purity and low defect can be grown; and the quality requirement on the epitaxial growth of high-quality ZnO films on a substrate can be met.

Description

Method for growing zinc oxide crystals by induction heating and pressure

technical field

The invention relates to a method for growing zinc oxide crystals, in particular to a method for growing ZnO crystals by adopting a medium frequency induction heating pressure temperature gradient method in an induction heating pressure crystal growth device.

Background technique

In recent years, based on the realization of ultraviolet lasers, ZnO has become one of the research hotspots in the field of semiconductor materials. Compared with other wide bandgap materials such as SiC and GaN, ZnO has the characteristics of abundant resources, low price and good stability. ZnO single crystal is a multifunctional crystal with semiconducting, luminescent, piezoelectric, electro-optic, and scintillation properties. It will soon become the next generation of optoelectronic materials and has a very broad application prospect. Not only that, in order to better study the semiconductor properties of ZnO, it is also necessary to synthesize high-quality ZnO bulk single crystals. However, since its melting point is as high as 1975°C, its sublimation phenomenon is severe at high temperatures (above 1400°C), and it also has strong polar crystallization characteristics, so the crystal growth is extremely difficult. As early as the 1960s, people began to pay attention to the growth of ZnO single crystals. Although many growth processes were tried, the resulting crystals were very small in size, generally on the order of millimeters, and had no practical value. In view of the great difficulty in bulk single crystal growth, people gradually turned their attention to the growth research of ZnO thin films, and once neglected the exploration of bulk single crystal growth process. Recently, with the rapid development of GaN, SiC and other new optoelectronic material industries, the demand for high-quality, large-size ZnO single crystal substrates is also increasing, and the research on the growth of ZnO bulk single crystals has attracted the attention of scientists again.

At present, large-size ZnO crystals are mainly prepared by hydrothermal method at home and abroad. There are relatively high concentrations of lithium and sodium in ZnO crystals prepared by hydrothermal method. These impurities will diffuse into the ZnO film during the film growth process, thereby reducing the crystalline quality of the film. .

Contents of the invention

The object of the present invention is to provide a method for growing zinc oxide crystals by induction heating and pressure, which includes an induction heating and pressure crystal growth device. This method has the advantages of stable temperature field and crystal growth interface, low growth pressure (<4MPa), short growth cycle, high crystal purity, simple growth device and easy control, etc., and can grow high-purity, low-defect ZnO crystals to meet the requirements of epitaxy. Growth of high-quality ZnO thin film requires the quality of the substrate.

Technical solution of the present invention is as follows:

A method for growing zinc oxide crystals by induction heating pressure temperature gradient method, comprising an induction heating pressure crystal growth device, characterized in that: during the crystal growth process, the furnace is filled with _CO2 and Ar or ( _N2) with a pressure of 1-4MPa The mixed gas, in which the volume ratio of _CO2 is 2% to 15%, is heated by the medium frequency induction iridium crucible; the iridium crucible is conical, and the conical part has a seed crystal on the head, and the lower end of the seed crystal is water-cooled Iridium pads; the conical part of the crucible is placed in a zirconia insulation barrel, the outer layer is filled with alumina hollow balls, and the outer part of the crucible is filled with zirconia powder as an insulation layer, and the outer layer of the zirconia powder is fixed by a quartz tube; The crystal and the melt are connected with thermocouples, which can detect the temperature of each place at any time; heat the zinc oxide raw material in the crucible until it melts, and then slowly cool down, so that the melt slowly crystallizes along the seed crystal until the crystal growth is completed .

^The method for growing zinc oxide crystals by induction heating and pressure _is to fill _a mixed gas ( The volume ratio of CO ₂ is 2% to 15%) to grow crystals by means of induction heating pressure temperature gradient method. By adjusting heat sources such as induction coils, zirconia insulation barrels, zirconia powder and alumina hollow balls and insulation materials, the temperature field gradient of the device is in the atmosphere of 20-80°C/cm; the cooling rate of the crystal growth process is 1-20°C / hour, the cooling rate after the growth is 20-100 ° C / hour, the cooling rate drops to 200 ° C, turn off the power and cool to room temperature with the furnace, and take out the crystal.

Technical effect of the present invention:

Compared with the traditional method, the direct induction crucible heating greatly improves the heating efficiency; the appropriate temperature gradient can be adjusted according to the size, position and insulation material relationship of the induction coil, and the crystal solid-liquid interface in the process of growing zinc oxide crystals by the melt method is optimized. The temperature gradient is difficult to control and adjust, which is conducive to the automatic control of crystal growth. The induction heating method is used to grow crystals. The insulation system is simple to manufacture, not easy to deform, and the cost is relatively low. The requirements for power supply and furnace performance are relatively low, and the overall cost is reduced.

The method of the invention overcomes the shortcomings of relatively high impurity concentration, long growth period, and high growth pressure (120 MPa) in the ZnO crystal prepared by the hydrothermal method, and has the advantages of stable temperature field and crystal growth interface, low growth pressure (<4 MPa), and high growth rate. With the advantages of short cycle, high crystal purity, simple growth device and easy control, ZnO crystals with high purity and low defects can be grown to meet the quality requirements of epitaxial growth of high-quality ZnO thin films on substrates.

Description of drawings

Fig. 1 is the structural schematic diagram of the temperature gradient furnace used for the induction heating pressure growth zinc oxide crystal of the present invention

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Embodiment 1: Adopt the method described in the present invention to grow the zinc oxide crystal of diameter Φ30

First, by adjusting the size and position of the induction coil and the relationship between the insulation materials, the temperature gradient of the temperature field of the device is 20°C/cm, and the zinc oxide raw material and seed crystal (the direction of the seed crystal is 0001 direction) are loaded into the iridium crucible , and install the induction heating furnace as shown in Figure 1, in the figure: 1-stainless steel furnace body, 2-quartz cylinder, 3-induction coil, 4-zirconium sand, 5-iridium gold crucible, 6 melt, 7-seed crystal, 8-alumina plate, 9-polytetrafluoroethylene, 10-base bolt, 11-iridium gold crucible cover, 12-zirconia heat preservation cover, 13-thick heater, 14-coil support, 15-alumina hollow ball, 16-zirconia insulation bucket, 17-iridium gold block, 18-polytetrafluoroethylene bolt, 19-seed crystal cooling water pipe, 20-thermocouple. Evacuate to a vacuum degree of better than 6×10 ^-2 Pa, fill in a mixed gas of CO ₂ and Ar or (N _{2 )} with a pressure of 4 MPa (the volume ratio of CO ₂ is 2%), and start to heat up to melt the raw materials , by observing the temperature of the thermocouple, adjust the appropriate cooling rate, and grow the crystal at a cooling rate of 1°C/hour. After the crystal growth is completed, the cooling rate is 100°C/hour and drop to 200°C. Take out the crystal at room temperature, and grow a zinc oxide crystal with a crystal size of Φ30×50 mm ³ .

Embodiment 2: Adopt the method described in the present invention to grow Φ30 zinc oxide crystal

First, by adjusting the size and position of the induction coil and the relationship between the insulation materials so that the temperature gradient of the device’s temperature field is 30°C/cm, the zinc oxide raw material and seed crystal (the direction of the seed crystal is 0001 direction) are loaded into the iridium crucible, And install the induction heating furnace as shown in Figure 1, evacuate until the vacuum degree is higher than 6×10 ^-2 Pa, and fill in the mixed gas of CO ₂ and Ar(N ₂ ) with a pressure of 1.5 MPa (wherein CO ₂ occupies The volume ratio is 5%), start to heat up and melt the raw materials, adjust the appropriate cooling rate by observing the temperature of the thermocouple, grow the crystal at a cooling rate of 20°C/hour, and grow the crystal at a cooling rate of 80°C/hour after the crystal growth ends The cooling rate was reduced to 200°C, the power was turned off and the furnace was cooled to room temperature, and the crystals were taken out. Zinc oxide crystals with a crystal size of Φ30×50mm ³ were grown.

Embodiment 3: Adopt the method described in the present invention to grow Φ35 zinc oxide crystal

First, by adjusting the size and position of the induction coil and the relationship between the insulation materials, the temperature gradient of the temperature field of the device is 80°C/cm, and the zinc oxide raw material and seed crystal (the direction of the seed crystal is 0001 direction) are loaded into the iridium crucible, And install the induction heating furnace as shown in Figure 1, evacuate until the vacuum degree is higher than 6×10 ^-2 Pa, and fill in the mixed gas of CO ₂ and Ar(N ₂ ) with a pressure lower than 4MPa (wherein CO ₂ occupies The volume ratio is 15%) and then start to heat up to melt the raw materials. By observing the temperature of the thermocouple, adjust the appropriate cooling rate, and grow the crystal at a cooling rate of 10°C/hour. The cooling rate was reduced to 200°C, the power was turned off and the furnace was cooled to room temperature, and the crystals were taken out. Zinc oxide crystals with a crystal size of Φ35×50mm ³ were grown.

Embodiment 4: Adopt the method described in the present invention to grow Φ35 zinc oxide crystal

First, by adjusting the size and position of the induction coil and the relationship between the insulation materials, the temperature gradient of the temperature field of the device is 40°C/cm, and the zinc oxide raw material and seed crystal (the direction of the seed crystal is 0001 direction) are loaded into the iridium crucible, And install the induction heating furnace as shown in Figure 1, evacuate until the vacuum degree is higher than 6×10 ^-2 Pa, and fill in the mixed gas of CO ₂ and Ar(N ₂ ) whose pressure is lower than 3MPa (wherein CO ₂ occupies The volume ratio is 8%), start to heat up and melt the raw materials, adjust the appropriate cooling rate by observing the temperature of the thermocouple, grow the crystal at a cooling rate of 15°C/hour, and grow the crystal at a cooling rate of 80°C/hour after the crystal growth ends The cooling rate was reduced to 200°C, the power was turned off and the furnace was cooled to room temperature, and the crystals were taken out. Zinc oxide crystals with a crystal size of Φ35×50mm ³ were grown.

Embodiment 5: Adopt the method described in the present invention to grow Φ40 zinc oxide crystal

First, by adjusting the size and position of the induction coil and the relationship between the insulation materials so that the temperature gradient of the device’s temperature field is 50°C/cm, the zinc oxide raw material and seed crystal (the direction of the seed crystal is 0001 direction) are loaded into the iridium crucible, And install the induction heating furnace as shown in Figure 1, evacuate until the vacuum degree is higher than 6×10 ^-2 Pa, and fill in the mixed gas of CO ₂ and Ar(N ₂ ) with a pressure lower than 2.5 MPa (wherein CO ₂ is accounted for 12% of the volume ratio), start to heat up to melt the raw materials, adjust the appropriate cooling rate by observing the temperature of the thermocouple, and grow the crystal at a cooling rate of 5°C/hour, and grow the crystal at a cooling rate of 60°C/hour after the crystal growth is completed. The cooling rate was reduced to 200°C, the power was turned off and the furnace was cooled to room temperature, and the crystals were taken out. Zinc oxide crystals with a crystal size of Φ40×50mm ³ were grown.

Embodiment 6: Adopt the method described in the present invention to grow Φ40 zinc oxide crystal

First, by adjusting the size and position of the induction coil and the relationship between the insulation materials so that the temperature gradient of the device’s temperature field is 35°C/cm, the zinc oxide raw material and seed crystal (the direction of the seed crystal is 0001 direction) are loaded into the iridium crucible, And install the induction heating furnace as shown in Figure 1, evacuate until the vacuum degree is higher than 6×10 ^-2 Pa, and fill in the mixed gas of CO ₂ and Ar(N ₂ ) with a pressure lower than 3.5 MPa (wherein CO ₂ is accounted for 7% of the volume ratio), start to heat up to melt the raw materials, adjust the appropriate cooling rate by observing the temperature of the thermocouple, and grow the crystal at a cooling rate of 8°C/hour, and grow the crystal at a cooling rate of 100°C/hour after the crystal growth is completed. The cooling rate was reduced to 200°C, the power was turned off and the furnace was cooled to room temperature, and the crystals were taken out. Zinc oxide crystals with a crystal size of Φ40×50mm ³ were grown.

Experiments show that the present invention can grow large-size and high-quality zinc oxide crystals at lower power consumption and lower cost, and can adjust the appropriate temperature gradient according to the size, position and insulation material of the induction coil, and optimize the use of the melt method In the process of growing zinc oxide crystals, the temperature gradient at the crystal-solid-liquid interface is difficult to control and adjust, which is beneficial to realize the automatic control of crystal growth. Moreover, the heating and heat preservation system is simple to manufacture, not easy to deform, stable in temperature field, and can be used for a long time.

Claims (1)

1. the method for an induction heating developing zinc oxide crystallite adopts induction heating pressure gradient furnace to grow, and its characteristics are:

In crude zinc oxide materials and seed crystal (seed crystal direction the be 0001 to) Iridium Crucible of packing into, be evacuated to vacuum tightness and be higher than 6 * 10 ^-2Behind the Pa, be filled with the CO that pressure is 1～4MPa in the crystal growing process in the burner hearth ₂With Ar or N ₂Mixed gas, CO wherein ₂Shared volume ratio is 2%～15%, through Frequency Induction Heating Iridium Crucible (5); Iridium Crucible (5) is placed with seed crystal (7) for round shape awl bottom structure at the awl end, and there is water-cooled iraurite cushion block (17) the seed crystal lower end; Be placed in bottom Iridium Crucible (5) awl in the zirconium white insulated tank (16), skin is filled alumina hollow ball (15), and zirconia powder (4) is filled as thermal insulation layer in the periphery of the cylinder of Iridium Crucible (5), and zirconia powder (4) outer use quartz tube (2) is fixed; Locate to be connected to respectively thermopair (20) at seed crystal and melt (4), can detection at any time temperature conditions everywhere;

Through regulating warm field gradient that ruhmkorff coil, zirconium white insulated tank, zirconium sand and alumina hollow ball make this device in 20～80 ℃/cm atmosphere;

Crude zinc oxide materials is to fusing in the heating crucible; The crystal growing process rate of temperature fall is 1～20 ℃/hour; Make melt along upwards slowly crystallization of seed crystal; Until accomplishing crystal growth; Be that 20～100 ℃ of/hour cooling rates are reduced to 200 ℃ with speed behind the growth ending; Powered-down cools to room temperature with the furnace, takes out crystal.

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