Optical Properties of III-Nitride Semiconductors

• Main Authors: Jeng-Wei Yu, 游政衞
• Other Authors: 馮哲川
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/79830406758231753486

碩士 === 國立臺灣大學 === 光電工程學研究所 === 93 === This thesis concerns with the studies on the optical properties of III-Nitride semiconductors. X-ray diffraction (XRD), Photoluminescence (PL) , Raman scattering (RS), Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) are carried out to study the physical properties of III-nitride materials, including AlxGa1-xN, InxAlyGa1-x-yN, Cu-implanted GaN and Si-doped GaN. Many peculiar phenomena have been observed, which are very useful for understanding as well as application of III-nitride materials. (1)Optical properties in (In,Al)GaN We use two different X-ray analysis techniques; a Williamson Hall plot and reciprocal space mapping to obtain their threading dislocation densities for GaN, AlxGa1-xN and InxAlyGa1-x-yN epitaxial layers. A WH plot can provide information about coherence length and tilt angle from a linear fit to the line-width of the triple axis rocking curve (000l) symmetric reflections. RSM is typically used to obtain this data, but it is more involved in technique. We also report excitonic optoelectronic properties of InxAlyGa1-x-yN quaternary alloys, including PL and Raman measurements. Then, we perform scanning electron microscopy (SEM) image and atomic force microscopy (AFM) to observe the InGaN-like clusters. (2)Characterization of Cu-implanted GaN We present SEM, low temperature PL, RS and XRD in Cu-implanted GaN. Due to Cu+ ions, we can observe the V-defects from SEM image. Using PL spectrum, we calculate a value for the Cu shallow accepter energy of 200 meV. We find three additional modes in Raman spectra for Cu-implanted GaN. The implantation-induced peaks are mainly categorized into : disorder activated Raman scattering and scattering mechanisms of implantation induced defects. From XRD curves, we observed the lattice expansion in the implanted layer due to the incorporation of atoms into the interstitial sites of the host structure. Such expansion results in the compressive strain alone c axis in the neighboring un-implanted region. (3)Optical properties in Si-doped GaN We use FTIR to characterize these samples. Based on theoretical equations used to calculate the reflectance of the IR spectra, we can obtain film thickness, free carrier concentration and electron mobility of Si-doped GaN. Photoluminescence and Raman scattering have been done on GaN grown on sapphire with different Si-doping concentration. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. From Raman scattering data, we discussed the influence of the carrier concentration for Raman spectra and observed the phonon-plasmon interaction effect for the GaN A1 (LO) mode.