Research On Optical Properties And Structure Of Indium Aluminum(Gallium) Nitride Thin Film For Semiconductor Material

The III-V group direct band gap semiconductor,InAlN,can be used to manufacture optoelectronic devices and power transistors.InAlN material has an adjustable band gap ranging from 0.7 to 6.2 e V,which has excellent thermochemical stability and a good lattice match with GaN when the In content is 17 at%.When using MOCVD(metal organic chemical vapor deposition)to grow InAlN/GaN heterojunction,the InAlN layer can be inadvertently doped with Ga due to the residue left on the reactor wall during the growth of the GaN layer or the diffusion of the GaN layer.Ga doping impacts the band gap,optical constants and surface quality of the InAlN epitaxial layer,thereby changing the receiving wavelength and efficiency of the related optoelectronic devices and the current handling capability of power transistors.Growing InAlN/GaN heterojunction is the basic step in making optoelectronic devices.It is critical to explore how to suppress the diffusion of Ga and the influence of Ga doping on the properties of InAlN.The InAl(Ga)N/GaN samples(The epitaxial layer doped with different concentrations of Ga)studied in this paper are grown on a sapphire substrate with different growth structures at the nanometer level using pulsed metal-organic chemical vapor deposition.Angular-resolved X-ray photoelectron spectroscopy is used to obtain the ratio of Ga,the chemical state and composition ratio of the surface elements,and the energy band shift in the sample surface.VASE is used to obtain the Information such as optical constants,band gap and film thickness,as well as the stability under high temperature.Raman spectroscopy is used to obtain the photo-generated LO mode phonon lifetime of the epitaxial layer at different temperatures.The specific research content and results of this article are as follows:(1)By comparing the Ga ratio of the InAl(Ga)N epitaxial layer at different depths,it is concluded that the main reason for Ga contamination is due to the diffusion of the Ga N layer.Simultaneously,it is found that the 2 nm Al N interlayer can effectively reduce the diffusion of Ga atoms to 0.7 at%,which can reduce the density of surface defects and improve the surface quality of the InAl(Ga)N layer.(2)By calculating the valence band shift,conduction band shift and band gap width,it is found that as the doping amount of Ga decreases from 0.7 at%to 6.4at%,the valence band shift of the InAl(Ga)N/GaN heterojunction is reduced from0.5 e V to 0.27 e V.When the Ga doping amount is 20.6 at%,the shift between InAl(Ga)N and GaN valence band comes to zero.In addition,the increase in Ga doping makes the heterojunction interface change from the I-type straddling gap to the II-type staggered gap.(3)The optical constants of the InAl(Ga)N layer grown by the PMOCVD method under the temperature of 800 K obtained by VASE can be successfully fitted by Varshni equation.Indicating that the physical properties of the epitaxial layer did not have a sudden change.At the same time,it is concluded that reducing the amount of Ga doping can make the stability of the layer higher,and the AlN inter layer can effectively improve the quality of the InAl(Ga)N film.(4)The temperature-varying Raman spectrum of the peak position and the half-width of the InAl(Ga)N layer A₁(LO)mode in the range of 80K-580K was successfully fitted by three-phonon process and the four-phonon process of anharmonic effect.Fitting shows that the samples with higher Ga doping concentration will decrease the phonon lifetime of the LO mode sharply at high temperature and reduce film stability.