A kind of method of improving GaN thick film integrality on sapphire substrate
One, technical field
The present invention relates to a kind of on Sapphire Substrate, carrying out and obtain the epitaxy method and the technology of complete flawless GaN thick film in hydride gas-phase epitaxy (HVPE) the growing GaN process.
Two, background technology
The III group-III nitride has broad application prospects in field of optoelectronic devices such as light demonstration, optical illumination.Aspect light demonstration and optical illumination, super large-screen and full color display and novel high-efficiency and energy-saving solid light source with the making of high efficiency blue-green light LED, useful life was above 100,000 hours, comparable incandescent lamp economize on electricity 5-10 doubly will worldwide cause an epoch-making deep revolution of lighting electric light source surely.At present, the research that GaN uses mainly concentrates on light-emitting diode (LED) and two aspects of laser diode (LD), and has obtained a series of progress.The invention of visual GaN semiconductor light-emitting-diode (LED) and laser diode (LD) and use have been bred very big business opportunity at commercial articles for use and consumer product area.
Because the fusing point high (~3000 ℃) of GaN, and about 1600 ℃, can decompose, be difficult to grow GaN monocrystalline more than 4 inches, can only accomplish 1 centimeter square especially at present, can not reach the requirement of making microelectronic component and opto-electronic device far away with traditional crystal technique.Lacking the high quality GaN backing material becomes the bottleneck of the high-end device of development GaN.Under the situation that direct growth GaN monocrystalline is difficult to, adopt other thick film growing technology to prepare the accurate monocrystal material of GaN and just had very important meaning.Hydride gas-phase epitaxy (HVPE) technology, growth rate height (can reach 300 microns/hour) is generally believed it is the most preferred technique of preparation GaN thick film, development self-supporting GaN substrate.The major advantage of HVPE technology comprises that equipment is simple relatively, the working service facility, and the quality of materials height of growth, growth rate is fast, is easy to obtain thick film, need not grown buffer layer etc.But it also has some technological difficulties, and as the consumption along with metal Ga source, growth rate may be affected; Attached the amassing in the pipeline downstream of byproduct of reaction ammonium chloride powder meeting may influence the air-flow in the pipeline, thereby influence growth quality.
Because the HVPE growing GaN has very high growth rate, just can obtain thicker GaN film in very short time.But the GaN film surpasses 50 microns on the Sapphire Substrate, and crackle will appear in film in temperature-fall period, and is of long duration, finally can be fragmented into several parts.This is one of key difficulties that obtains on the foreign substrate GaN thick film, is helpless to the application of GaN thick film,
In the present invention, the present invention proposes a kind of simple growth in situ technology, and the high low temperature GaN of growth in situ film improves the integrality of cooling back GaN thick film in hydride gas-phase epitaxy (HVPE) growing system.
Three, summary of the invention
The present invention seeks to: propose the process that stress in a kind of new reduction HVPE thick film improves GaN thick film integrality on the sapphire.
Technical solution of the present invention: improve the method for GaN thick film integrality on sapphire substrate, adopt HVPE technology, the reaction source material is gallium, HCl or trimethyl gallium, carrier gas NH
3Comprise the steps:
1), the substrate that adopts is sapphire or Si,
2), with above-mentioned substrate through after cleaning, drying up, put into the HVPE growing system, growth low temperature GaN resilient coating earlier, 550-750 ℃ of buffer growth temperature, growth time 30-300s;
3), growth temperature is increased to 850-950 ℃, under this temperature, carry out the GaN growth, time 30-300s;
4), keep the growth that begins to heat up of step 3 growth conditions, the GaN growth continues to carry out always in this process.Be promoted to 1050-1100 ℃ up to growth temperature, proceed the HVPE growth of GaN, up to the GaN film that obtains desired thickness; Intensification is alternating temperature growth heating-up time 0.5-2 hour, and the thickness of growing GaN film can not be lower than 50 microns in temperature-rise period;
5), growth slowly is cooled to room temperature after finishing, rate of temperature fall is not higher than 10 ℃/minute.
The present invention is in the hydride gas phase epitaxial growth system, growing GaN low temperature buffer layer on the first Sapphire Substrate at low temperatures, be warming up to higher temperature (less than final growth temperature) growing GaN film (high temperature GaN layer), limit intensification limit growth in temperature-rise period is subsequently carried out thicker GaN growth for Thin Film up to reaching last growth temperature.Adopt slow temperature reduction way cooling, reach room temperature and can obtain flawless GaN thick film.
Low temperature buffer layer among the present invention also can be the MOCVD GaN inculating crystal layer on the sapphire.
Mechanism of the present invention is: studies show that most of dislocation all is to concentrate on Sapphire Substrate and GaN film at the interface.Because sapphire and GaN lattice mismatch and thermal mismatching are all bigger, temperature-fall period can cause in the GaN sample that bigger stress, stress make GaN and sapphire generation deformation.In temperature-fall period, this deformation meeting makes sample cracked.Low temperature buffer layer that we adopt and high temperature GaN resilient coating can hinder dislocation and further extend to the GaN film surface, reduce dislocation density, and the strain that causes of release portion lattice mismatch.And the more effectively generation of relieve stresses of the growth of the GaN in temperature-rise period forms suitable ess-strain releasing layer.Finally obtain the GaN thick film on the complete flawless Sapphire Substrate.
The invention has the beneficial effects as follows, can obtain 2 inches of large tracts of land (〉) and also complete flawless Sapphire Substrate on the GaN thick film.
Four, description of drawings
Fig. 1 is the growth technique structural representation of the GaN thick film of HVPE of the present invention.Elder generation's growth low temperature buffer layer or (MOCVD inculating crystal layer), the high temperature GaN layer of growing then and continued growth in the process that further heats up are up to reaching final growth temperature, the growth of lasting thick film.
Five, embodiment
The intensification that the present invention adopts is an alternating temperature GaN thin film technique, and the side that improves GaN thick film integrality on sapphire substrate comprises following a few step: HVPE, the key reaction source material is a gallium, high-purity HCl, trimethyl gallium or other organic gallium source, carrier gas N2 and NH also can be adopted in the gallium source
3Deng;
1, the substrate of Cai Yonging can be sapphire, Si etc., also can adopt grown on these substrates inculating crystal layer of GaN of methods such as MOCVD, MBE or HVPE.
2, with after the cleaning of above-mentioned substrate process, drying up, put into the HVPE growing system, the HVPE growth of beginning GaN.Do not having on the substrate of inculating crystal layer, earlier growth low temperature GaN resilient coating.550-750 ℃ of buffer growth temperature, growth time 30-300s.What the GaN inculating crystal layer was arranged does not need growing low temperature GaN resilient coating, directly enters step 3.
3, growth temperature is increased to uniform temperature, is typically 850-950 ℃, under this temperature, carry out the GaN growth, time 30-300s.
4, keep step 3 growth conditions and begin the growth that heats up, the GaN growth continues to carry out always in this process.Be promoted to final growth temperature (1050-1100 ℃) up to growth temperature, proceed the HVPE growth of GaN, up to the GaN film that obtains desired thickness.Intensification is that the alternating temperature growth did not wait in heating-up time 0.5-2 hour, decides on growth rate.The thickness of alternating temperature growing GaN film can not be lower than 50 microns in temperature-rise period.
5, slowly be cooled to room temperature after growth is finished, rate of temperature fall is not higher than 10 ℃/minute.
The GaN thick film that obtains of growth like this, flawless can be kept perfectly.
The inculating crystal layer growth is the control growing method of GaN thin-film material, in the MOCVD system, grow, do backing material by the R surface sapphire of selecting [1120], at first, in the MOCVD system R surface sapphire substrate of growth is carried out material heat treatment under 900-1100 ℃ of temperature, the time is 5-60 minute; Probable back feeding ammonia carries out surfaces nitrided, is 10-120 minute 900-1100 ℃ of following time of temperature; Feed H 900-1100 ℃ of temperature range again
2And/or N
2As carrier gas, ammonia and metal organic gallium source as the growth source of the gas; By the control carrier gas, growth source of the gas gas flow and growth temperature parameter, a face or the m face GaN material of synthetically grown non-polar plane on the Sapphire Substrate of the substrate crystal face of selecting.Feed carrier gas H
2, N
2Or H
2With N
2Mist carries out material heat treatment to the R surface sapphire substrate under 900-1100 ℃ of temperature.The metal organic gallium source is a trimethyl gallium, and flow is 1-50sccm, and the time is 10-60 minute, NH
3Gas 200-700sccm, V/III is than being 200-3000, the i.e. mol ratio of N and Ga.H
2Or N
2Or H
2And N
2Air-fuel mixture enleanment throughput 2500-3500sccm; NH
3Gas 200-700sccm, especially 500-700sccm.