Raman Studies of Wide Band Gap Semiconductors: GaN, InGaN and SiC
Date Issued
2007
Date
2007
Author(s)
Lien, Siou-Cheng
DOI
en-US
Abstract
A series of optical characterization techniques, including Raman scattering, Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), photoluminescence excitation (PLE) and X-ray diffraction (XRD), were employed to assess wide band gap semiconductors which are semiconductor materials with electronic band gaps larger than an electronvolt (eV) or two. They have been expected to be applied to various optoelectronic devices such as light emitting diodes (LED), lasers, and electron-beam sources. In this thesis, we study the optical properties, especially on Raman scattering, of gallium nitride (GaN), indium gallium nitride (InGaN) and silicon carbide (SiC).
We use different structures of samples to do experiments and can summarize that GaN/AlGaN/HT-GaN/LT-GaN multilayer and HT-GaN layers affect the performances of GaN films grown on Si substrate very much from chapter 3. The GaN/AlGaN/HT-GaN/LT-GaN multilayer can decrease the strain of GaN films and increase their qualities. The HT-GaN layer can help the growth of AlGaN layer and let the multilayer perform well.
At chapter 4, we have experimental data to confirm the successful growth of the InGaN on ZnO with a GaN buffer layer and poor performance of GaN film grown on ZnO substrate because of the diffusion of Zn and O into the GaN layer. Because ZnO is a wurtzite semiconductor with a small c-plane lattice mismatch of 1.8% from wurtzite GaN, we expect a good quality of GaN films grown on ZnO substrate. And InGaN, a GaN-based alloy with a composition of 18% In, also possesses a perfect lattice-match with ZnO in the a-axis direction. Due to that MOCVD is the dominant growth technology for GaN-based materials and devices, there is a need to more fully explore this technique for ZnO substrates. However, there is a problem for MOCVD growth of GaN and InGaN on ZnO substrates in different requested growth temperature. We can’t get the PL spectrum of GaN film grown on ZnO substrate and there is a red shift of the PL spectrum coming from InGaN film. The reason is the diffusion of Zn and O.
Finally, we study Raman scattering on 4H-SiC with two varied factors: temperature and free carrier concentration. There are many journals and reports of LOPC modes on high doping samples. And there are also many discussions about temperature-dependent Raman scattering. But we find out an unusual dependence of the LOPC mode shift with temperature in chapter 5. We suppose that it results from excited plasma by increasing temperature.
Subjects
拉曼散射
氮化鎵
氮化銦鎵
碳化矽
Raman scattering
GaN
InGaN
SiC
Type
thesis
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