CN1322175C - Preparation of gamma-LiAlO by pulsed laser deposition2Method for covering substrate with single crystal thin film - Google Patents

Abstract

Preparation of gamma-LiAlO by pulsed laser deposition₂The method for covering the substrate with a single crystal thin film comprises first coating gamma-LiAlO₂Then using pulsed laser deposition to deposit gamma-LiAlO₂The surface molecules of the target material are melted and evaporated, and heated alpha-Al is added₂O₃Or depositing on silicon substrate to generate gamma-LiAlO₂A monocrystalline thin film cap layer. The method has simple process and easy operation, and the substrate with the structure is suitable for the epitaxial growth of high-quality GaN.

Description

Method for preparing γ-LiAlO2 single crystal thin film cover layer substrate by pulsed laser deposition

technical field

The invention relates to the epitaxial growth of InN-GaN-based blue-light semiconductors, in particular to a method for preparing a gamma- _LiAlO2 single-crystal film covering layer substrate by pulse laser deposition. This substrate material is mainly used for epitaxial growth of InN-GaN-based blue light semiconductor.

Background technique

Wide bandgap III-V compound semiconductor materials represented by GaN are attracting more and more attention, they have excellent characteristics, such as stable physical and chemical properties, high thermal conductivity and high electron saturation velocity, direct bandgap materials The probability of optical transition is an order of magnitude higher than that of indirect bandgap, so wide bandgap InN-GaN-based semiconductors are widely used in blue and green light-emitting diodes (LEDs) and laser diodes (LDs), high-density information reading and writing, underwater communication, deep water detection, It has broad application prospects in laser printing, biological and medical engineering, as well as ultra-high-speed microelectronic devices and ultra-high-frequency microwave devices. Due to the relatively high melting point of InN-GaN and the high saturated vapor pressure of N ₂ , it is very difficult to prepare InN-GaN bulk single crystals, so InN-GaN is generally grown on heterogeneous substrates by epitaxial technology.

Due to GaN's high melting point, high hardness, and high saturated vapor pressure, high temperature and high pressure are required to grow large-sized GaN bulk single crystals. The Polish High Pressure Research Center only produced strips with a width of 5 mm at a high temperature of 1600 ° C and a high pressure of 20 kbar. GaN bulk single crystal. At present, the technology to grow large-sized GaN bulk single crystal is still immature, and the cost of growth is high, and there is still a long distance from practical application.

Sapphire crystal (α-Al ₂ O ₃ ), silicon, etc. are easy to prepare, cheap, and have good high temperature stability. α-Al ₂ O ₃ is currently the most commonly used InN-GaN-based epitaxial substrate material. See Jpn. J. Appl. Phys., Vol. 36, 1997, p. 1568.

Lithium aluminate (γ-LiAlO ₂ ) is an InN-GaN-based epitaxial substrate material that has only received attention in recent years. Because of its very small lattice mismatch with GaN epitaxial film, only 1.4%, it is expected to become A rather ideal GaN epitaxial substrate material, see USP6218280B1, Kryliouk Olga, Anderson Tim, Chai Bruce, "Method and apparatus for producing group-III nitrides".

The significant disadvantages of the above-mentioned prior art substrate (α-Al ₂ O ₃ , silicon or γ-LiAlO ₂ ) are: (1) use α-Al ₂ O ₃ , silicon, etc. as the substrate, and between the substrate and GaN The high degree of lattice mismatch makes the prepared GaN film have a high dislocation density and a large number of point defects; (2) due to LiAlO ₂ melt is prone to non-stoichiometric volatilization at high temperature, crystal growth is difficult, and it is difficult to obtain Large-sized, high-quality LiAlO ₂ single crystal, the largest sapphire diameter reaches 350mm, while the diameter of LiAlO ₂ is less than 100mm, and the processing of the substrate will cause a lot of waste of raw materials.

Contents of the invention

The technical problem to be solved in the present invention is to overcome the above-mentioned shortcoming of prior art, provide a kind of pulse laser deposition and prepare the method for gamma-LiAlO ₂ single crystal film covering layer substrate, this method should have simple process, easy operation, this kind of structure The substrate is suitable for the epitaxial growth of high-quality GaN.

Based on the above considerations, the key point of the present invention is to use pulsed laser deposition (PLD: pulsed laserdeposition) technology to generate a γ-LiAlO ₂ capping layer on α-Al ₂ O ₃ or a silicon substrate, where α-Al _{2 O3} or silicon acts as a support for the thin layer of γ- _LiAlO2 on it. The substrate with this structure is suitable for the epitaxial growth of high-quality GaN thin film.

The method of the present invention mainly includes two steps: firstly, the preparation of γ-LiAlO ₂ , and then using pulse laser deposition to prepare the γ-LiAlO ₂ covering layer on the α-Al ₂ O ₃ or silicon substrate.

Pulse laser deposition (PLD) of the present invention prepares γ-LiAlO The concrete technological process of the method for _single crystal thin film cover layer substrate is as follows:

<1>Preparation of γ-LiAlO ₂ target material: Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere and keep the temperature at 600°C for a full reaction for 1.5h (above), you can get γ-LiAlO ₂ . The chemical reaction formula is as follows:

2LiOH+Al ₂ O ₃ →2γ-LiAlO ₂ +H ₂ O↑

Then the γ- _LiAlO2 powder was pressed into the target.

<2> Send the cleaned α-Al ₂ O ₃ or silicon wafer substrate and γ-LiAlO ₂ target into the pulsed laser deposition device;

<3> Evacuate the cavity into an ultra-high vacuum, and then fill it with argon atmosphere;

<4>Heat the substrate to 500-900°C, focus the KrF excimer laser through the lens, and irradiate the γ-LiAlO ₂ target in the device through the optical window, and the molecules on the surface of the target will melt on the substrate Deposit on the surface, grow a layer of γ-LiAlO ₂ single crystal thin film, after slow cooling, high-quality γ-LiAlO ₂ thin film can be obtained. Thus, a substrate material with a γ-LiAlO ₂ single crystal thin film covering layer is obtained. The substrate with this structure is suitable for the epitaxial growth of high-quality GaN.

The mechanism of the pulsed laser deposition (PLD) method is: a KrF ^excimer laser (laser wavelength of 248nm) with a pulse width of 25-30ns (nanoseconds) is concentrated through a lens with an energy density of about 10J/cm The window irradiates the γ- _LiAlO2 target in the device. After the target absorbs the laser light, it becomes a high-temperature molten state due to electronic excitation, so that the surface of the material is evaporated and gasified, and the gaseous particles are released in the form of columns. and are diffused, attached and deposited on the heated α-Al ₂ O ₃ or silicon substrate placed a few centimeters away from the surface of the target, thereby depositing a γ-LiAlO ₂ film.

Technical characteristics of the present invention are:

<1>, directly using γ-LiAlO ₂ as the target material, avoiding the reaction with the substrate to prepare the γ-LiAlO ₂ film, which is beneficial to control the thickness and uniformity of the γ-LiAlO ₂ film.

<2>. In this structure, α-Al ₂ O ₃ or silicon only plays the role of supporting the thin layer of γ-LiAlO ₂ on it. Different substrates can be used to support γ-LiAlO ₂ , which is beneficial to reduce costs . The substrate with this structure is suitable for the epitaxial growth of high-quality GaN.

Description of drawings

Figure 1 is a schematic diagram of a pulsed laser deposition (PLD) system.

Detailed ways

Please refer to FIG. 1 first. FIG. 1 is a schematic diagram of a pulsed laser deposition (PLD) device used in the method for preparing a substrate material with a γ-LiAlO ₂ single crystal thin film covering layer according to the present invention.

Below by embodiment the present invention will be further described. This embodiment adopts the device of Fig. 1, and its concrete technological process is as follows:

Example 1

<1> Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere to keep the temperature at 600°C, and fully react for 1.5 hours (above) to obtain γ -LiAlO ₂ . Then the γ- _LiAlO2 powder is pressed into the target material;

<2> Send the cleaned α-Al ₂ O ₃ or silicon substrate and γ-LiAlO ₂ target into the pulsed laser deposition device;

<3> Evacuate the cavity into a high vacuum (>10 ^-4 Pa), and then fill it with argon atmosphere;

<4>Heat the substrate, raise the temperature to 500°C, focus the KrF excimer laser with a pulse width of 25ns through the lens with an energy density of 10J/ ^cm2 , and irradiate the γ- _LiAlO2 target in the device through the optical window , the surface molecules of the target are melted and vaporized to form a film on the substrate, which can be obtained after slowly cooling down, thus obtaining a γ-LiAlO ₂ single crystal thin film.

Example 2

<1> Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere and keep the temperature at 500°C for 1.5 hours (above) to fully react to obtain γ- LiAlO ₂ . Then the γ- _LiAlO2 powder is pressed into the target material;

<2> Send the cleaned α-Al ₂ O ₃ or silicon substrate and γ-LiAlO ₂ target into the pulsed laser deposition device;

<3> Evacuate the cavity into a high vacuum (>10 ^-4 Pa), and then fill it with argon atmosphere;

<4> Heating the substrate to 600°C, focusing the KrF excimer laser with a pulse width of 25ns through the lens at an energy density of 10J/ ^cm2 , and irradiating it to the γ- _LiAlO2 target in the device through the optical window , the surface molecules of the target are melted and vaporized to form a film on the substrate, which can be obtained after slowly cooling down, thus obtaining a γ-LiAlO ₂ single crystal thin film.

Example 3

<1> Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere and keep the temperature at 600°C for 1.5 hours (above) to fully react to obtain γ- LiAlO ₂ . Then the γ- _LiAlO2 powder is pressed into the target material;

<2> Send the cleaned α-Al ₂ O ₃ or silicon substrate and γ-LiAlO ₂ target into the pulsed laser deposition device;

<3> Evacuate the cavity into a high vacuum (>10 ^-4 Pa), and then fill it with argon atmosphere;

<4> Heating the substrate to 900°C, focusing the KrF excimer laser with a certain energy density through the lens, and irradiating the γ-LiAlO ₂ target in the device through the optical window, and the molecules on the surface of the target are melted and vaporized Finally, a film is formed on the substrate, and the γ-LiAlO ₂ single crystal thin film can be obtained after slowly cooling down.

Experiments show that the method of the invention has simple process and easy operation, and the substrate with this structure is suitable for epitaxial growth of high-quality GaN.

Claims (2)

1. A method for preparation of γ-LiAlO by pulsed laser deposition ₂ single-crystal thin-film overlay substrates, characterized in that the method is: at first γ-LiAlO ₂ is prepared, and then deposited on α-Al ₂ O by pulsed laser deposition ₃ or prepare a γ-LiAlO ₂ capping layer on the silicon substrate. 2. The method for preparing a gamma- _LiAlO2 single crystal thin film cover layer substrate by pulsed laser deposition according to claim 1, characterized in that the method comprises the following specific steps: <1> Weigh a certain amount of LiOH and Al ₂ O ₃ in a molar ratio of 2:1, put them into a reaction vessel, heat them to 600°C in an air atmosphere, and keep them warm for ≥1.5 hours to fully react to obtain γ- LiAlO ₂ , and then press γ-LiAlO ₂ powder into the target; <2> Send the cleaned double-side polished or single-side polished substrate and γ- _LiAlO2 target into the pulsed laser deposition device; <3> Evacuate the cavity of the pulse laser deposition device into an ultra-high vacuum, and then fill it with argon; <4>Heat the substrate to 500-900°C, focus the KrF excimer laser through the lens, and irradiate the γ-LiAlO ₂ target in the device through the optical window. Deposit on the substrate, grow a layer of single crystal thin film, and after slow cooling, a high-quality substrate with γ-LiAlO ₂ single crystal thin film covering layer can be obtained.

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