Study On Optical Properties Of Nitride Semiconductor Materials Based On Ellipsometry Technique

In recent years,gallium nitride(GaN)and related materials have enabled many applications such as light emitting diodes(LED),blue/UV semiconductor lasers,high power electronic devices and solar cells.GaN is an excellent piezoelectric material,which exhibit small residual stress,can optimize the physical properties and the performance of optoelectronic devices.Indium gallium nitride(InGaN)tunable direct band gap,varying from 0.7 eV(InN)to 3.4 eV(GaN),covers a wide spectral range from infrared(IR)to ultraviolet(UV),making it suitable to serve for full-spectrum devices.Much attention and efforts have been contributed to the growth of high quality thin films high-In compositional InGaN.Similarly,aluminum gallium nitride(AlGaN)alloys are of great interest for the development of high-temperature,high-power and deep ultraviolet(UV)optoelectronic devices,due to their high thermal conductivity,high dielectric constant and continuously tunable bandgap.In this paper,the optical constants of GaN,InGaN and AlGaN were analyzed by ellipsometry technique for the optical properties of nitride semiconductor materials.The main contents of this paper are as follows:(1)The silicon-doped n-type GaN thin films grown on the c-plane sapphire substrate by metal organic chemical vapor deposition(MOCVD)were used for the multi-angle elliptically polarized spectroscopy at room temperature,and successfully simulated the GaN film and the GaN buffer layer by using Gaussian,The Psemi-Mo and Psemi-Tri oscillator models in the range of 193 nm-1650 nm.The reliable optical constants of the experimental samples can be obtained efficiently.We provide a new idea for the study of the energy band structure of the material.(2)The InxGa1-xN film samples with different In components grown using high-pressure chemical vapor deposition(HPCVD)were measured by multi-angle ellipsometry with the temperature range from room temperate to 600?.The optical constants of InXGa1-xN thin films were simulated by Tauch-Lorentz oscillator model.The fitting analysis of the elliptical data shows that the increase of the In component and the increase of the test temperature have the same trend on the InxGa1-xN optical constant.(3)The influence of A1 content and temperature(300 K-823 K)on optical properties of epitaxial AlxGa1-xN layers has been studied with high accuracy by spectroscopic ellipsometry.With increasing temperature,the refractive indices increase in the transparent region,and the optical bandgap values decrease for all studied samples.