Multiple Spectrum Technique Studies Of Indium Gallium Nitride Thin Film Materials For Solar Cell

As a material that can be used to develop fully spectral optoelectronic devices,InGaN alloy has been paid more and more attention in the industrial production of InGaN/GaN-based LED and in its use as a source of illumination around the world.In addition to the low indium parts of the blue LED,high indium composition of green,yellow and red LED is worth studying.The research purpose and motivation of this work are to promote the research and development of InGaN materials with high indium content grown directly on the sapphire substrate without buffer layer which were rarely reported in the literature,and deepen our understanding of these high Indium compositional InGaN epitaxial materials.The MEPA-MOCVD technique was employed to prepare a series of In-rich InGaN nanoscale epitaxial films with In composition varying between 50%to 80%,directly onto the sapphire substrates without using any buffer layers.Their structural,surface,optical and vibrational properties were studied thoroughly with the help of several material characterizations techniques.While high-resolution X-ray diffraction(HR-XRD)measurements were employed for determining the In-composition x in InxGa1-xN-the surface composition and morphology,the surface components and elemental chemical states of thin films are analyzed and determined by X-ray photoelectron spectroscopy(XPS),and the optical properties of the films are evaluated by Raman scattering Spectra(RSS)and variable angle spectral elliptic polarization(VASE).The main research contents of the thesis are carried out from the following aspects:(1)In-rich InGaN samples are tested by X-ray diffraction spectra and the data is fitted by software.The composition of the film are obtained by analysis.(2)InGaN samples are tested and analyzed by X-ray Electron Energy spectroscopy(XPS).XPS is a surface analysis technology,through the fitting calculation of each peak,the film surface components and the chemical state of each element are obtained.At the same time,the maximum value(VBM)of the valence band spectrum can be obtained,and then the valence band offset and the guide offset are calculated.The surface x(In)calculated by XPS are compared with the values of the entire film by HR-XRD.(3)The optical properties of films are studied by normal temperature and variable temperature VASE.Taking three incident angles for testing,with the spectral range ranges from 190nm to 1600nm(0.78-6.52eV),and test one of the samples by variable temperature VASE(30 ℃-600 ℃)to studying the optical constants of the film,such as refractive index n,extinction coefficient k,etc.,and the film thickness and surface roughness are also obtained in the same time.(4)The samples were tested by Raman scattering spectra.The phonons is analyzed with the theoretical model.By comparing the results of this experiment with the results of the existing research,the RSS results confirmed the one-phonon behavior for the A1(LO)and E2(high)modes with x(In)-independent of phonon frequencies of the substrate.