RAMAN SCATTERING IN GALLIUM NITRIDE GROWN BY METAL-ORGANIC CHEMICAL VAPOR DEPOSITIO

Abstract

In the present work, a detailed Raman scattering study on Gallium Nitride has been carried out using JY-T64000 Micro-Raman system. Raman analyses have been performed on both Wurtzite (WZ-GaN grown on sapphire) and cubic (ZB-GaN grown on GaAs) GaN samples grown by Metal Organic Chemical Vapor phonon Deposition (MOCVD). Symmetry allowed phonons of from hexagonal GaN as well TO and LO phonons from cubic GaN are recorded using various polarization configurations. Characteristic Raman spectra represent the crystal structure and symmetry of the GaN samples grown on different substrates and the results are consistent with the x-ray diffraction analysis. The Raman spectra of Si-doped WZ-GaN with different carrier concentration show the shifting of LO phonon band towards higher energy side and broadening with an increase in carrier concentration. This is due to the coupling of LO phonons with the overdamped plasmon in GaN. The carrier concentration and damping constants are determined by the lineshape fitting of the coupled modes. The carrier concentration determined from the Raman analysis shows excellent agreement with the data obtained from Hall measurements. Raman analysis of the phonon lifetimes in GaN are also presented. In order to ensure the accuracy of 2TOAE212E mode and shorter lifetime of modes. We found that density of states and impurity concentration greatly affect the lifetimes of the measurement of the phonon lifetimes, an experimental procedure to eliminate the broadening due to the finite slit width was performed. The analysis indicates that phonon lifetimes in GaN fall into two main )regimes: a relatively longer lifetime of the (1 LOAoptical phonons in GaN.