Aluminum Nitride Crystal Are Synthesized By Cu-Al-Ca Flux Method

As an ultra-wide band-gap semiconductor material,AlN has excellent properties such as wide band-gap,high thermal conductivity,high critical breakdown field strength and excellent electronic properties.It has been widely used in many fields such as substrate materials,light-emitting diodes,laser diodes,pressure sensors,surface acoustic devices and high temperature and high pressure optoelectronic devices.In recent years,the growth of AlN single crystals has been widely studied by researchers all over the world,but because of its unique physical and chemical properties,it is still difficult to prepare large size and high quality AlN single crystals.At present,physical gas phase transfer（PVT）and cosolvent method are the main growth methods for AlN single crystal.PVT technique is developed and mature,it is the only method that can grow large size and high quality AlN single crystal.Nevertheless,the color of AlN single crystal obtained by PVT method is yellowish brown,also the high temperature corrosion resistance of the growth system is required during the growth process.Compared with PVT method,flux method has the advantages of high growth quality and low growth cost.Therefore,in this paper,the epitaxial growth of AlN single crystal by Cu-Al-Ca flux method is used to explore the influencing factors of crystal growth.The Cu-Al-Ca flux system,graphite crucible,AlN substrate and seedless crystal rod structure were determined by experiments.By comparing the conditions of different flux ratio,different nitrogen/argon ratio and different growth time,the optimum growth conditions of Cu:Al ratio of 47:50,nitrogen/argon ratio of 7:3 and growth time of 5h were determined.The surface morphology and crystal quality of AlN epitaxial layer growing under different growth conditions were analyzed.Through the preliminary experimental exploration and optimization of experimental parameters,AlN epitaxy layer more than 50μm thick homogeneous epitaxy was grown on the AlN seed crystal.It was observed by optical microscope that the growth surface morphology of Al-polar and N-polar was obviously different.The full-width at half-maximum of the oscillating curve of the grown AlN epitaxial layer were characterized by high resolution X-ray diffraction（The FWHM values of the（002）and（102）rocking curves were 160.25 and33.53 arcsec,respectively.）.The analysis of Raman spectra shows that the crystal quality of epitaxial layer is higher than that of seed crystal,and the crystal quality of N-polar is higher than that of Al-polar(N-polar from 7.4 cm^-1 to 6.1 cm^-1,Al-polar from13.9 cm^-1 to 10.6cm^-1),and the growth rate of N-polar is higher than that of Al-polar（N-polar 10-12μm/h,Al-polar 7-10μm/h）.Three emission peak defects at 310 nm,460nm and 590 nm were identified by photoluminescence spectra,and the causes of these defects were explained respectively.