Studys On The Structure,Optical And Surface Properties Of Aluminum Nitride Crystals And Films

Aluminum nitride is an important direct wide band gap semiconductor material with high stability,high resistivity,high thermal conductivity and high breakdown field;in the fields of high-density optical data storage,solid-state light sources,diodes,substrate materials,and air disinfection devices related to biomedical research have broad applications.As we all Know,there is a large lattice mismatch and thermal expansion coefficient mismatch between the aluminum nitride and substrate.Aluminum nitride films grown on sapphire usually exhibit high linear density misalignment and aluminum nitride films grown by metal organic chemical vapor deposition(Metal-Organic Chemical Vapor Deposition,MOCVD)also have high screw dislocation density.These defects provide non-radiative recombination centers or leakage current paths,which greatly reduces device performance.In addition,there are some problems with aluminum nitride films grown on 6H-Si C.There is also a large lattice mismatch and thermal expansion coefficient mismatch between Si C and AlN,which makes silicon carbide easy to decompose.At the same time,in terms of AlN single crystals,the problem of how to grow large-size,uniform color and high-quality AlN crystals has not been solved yet.Based on the above problems,this thesis analyzes the optical properties of a series of AlN heterojunction films and AlN crystals grown on different substrates by means of multispectral methods(Raman/temperature-variable scattering spectroscopy,ellipsometric polarization spectroscopy,and photoluminescence spectroscopy).Supplemented by high-resolution X-ray diffraction,atomic force microscopy and X-ray photoelectron spectroscopy to analyze its structure and surface properties,providing valuable research results for the preparation of high-quality and high-performance AlN-based devices.The research content of the thesis includes:(1)The comparison and analysis of three AlN crystals grown by the physical vapor transport method(two grown along the c plane and one grown along the m plane)by normal temperature/variable temperature Raman,the research results show that the crystal quality of AlN crystals grown along the c plane is better than that of the AlN crystals grown along the m plane,and the residual stress of the AlN crystal grown on the c plane is smaller than that of the AlN crystal grown on the m plane.From low temperature to high temperature,the residual tensile stress in the three AlN crystals is gradually increasing.At the same time,the stress sensitivity of temperature to the AlN crystal grown on the m plane is greater than the stress sensitivity of the AlN crystal grown on the c plane.(2)Through high-resolution X-ray diffraction,X-ray photoelectron spectroscopy,normal temperature/variable temperature Raman scattering spectroscopy,and ellipsometry,the structure and optical properties of AlN films grown on sapphire with different crystal planes were analyzed.The main orientation crystal planes,surface element composition,aluminum-nitrogen atomic ratio,thickness,roughness and optical band gap of AlN films grown on A,C,and R-plane sapphire are obtained.Studies shown that the crystal defects of the AlN film grown on the C-plane sapphire are more than the other two(A-plane and R-plane sapphire)of the AlN film grown by three magnetron sputtering,and the A-plane sapphire has more defects than the other two(A-plane and R-plane sapphire).The crystal quality of the AlN film is the best among the three.At the same time,the variable temperature Raman spectrum shows that the three AlN films have residual tensile stress in the entire temperature range.In summary,in order to improve the crystal quality of the AlN film,we need to further adjust our growth parameters.(3)the structure,surface and optical properties of AlN films grown on C-plane sapphire and 6H-Si C were analyzed by various characterization techniques(photofluorescence spectroscopy,high resolution X-ray diffraction,X-ray photoelectron spectroscopy,Raman scattering spectroscopy at room temperature/variable temperature,ellipsometric polarization spectroscopy,transmission spectroscopy and atomic force microscopy).Using the above different techniques to study AlN films,the main orientation crystal planes,surface composition elements,aluminum-nitrogen ratio,thickness,optical band gap,roughness,dislocation density and micro-strain of AlN films grown on heterogeneous substrates are obtained.The results show that the crystal quality of AlN film grown on 6H-SiC is better than that of AlN film grown on sapphire substrate.Through further analysis of the variable temperature Raman spectra,we found that when the temperature rises from 80K to 800K,the biaxial stress in the AlN film will suddenly change from compressive stress to tensile stress.At the same time,the temperature mutation point of AlN film grown on sapphire is higher than that of AlN film grown on 6H-SiC.