Study On Raman Scattering Of Gallium Nitride Films With Different Polarity

Possessing a wide band gap and large break down field, gallium nitride (GaN) is ofinterest for a host of high power, high frequency applications. Despite majorachievements in the growth and fabrication of high-quality AlGaN/GaN devicestructures, there are still a large number of material defects in GaN films due tomismatch between films and the substrates, which strongly limits the application ofGaN in elctronics and optoelectronics. As a non-destructive, contactless, fast,convenient and effective technique, Raman scattering has been proved to be playing thekey role for studying various aspects of solids such as lattice properties, electronicproperties, and magnetic properties. This thesis concerns studies of Raman scattering inGaN-based semiconductor materials.Firstly, the lattice vibrational properties of hexagonal GaN have been analyzed, theemphasis is on the influences of the free carrier concentration and aluminiumcomposition on Raman modes.Secondly, the Raman tensors applicable to wurtzite material have been introduced, theexpected experimental Raman scattered signals have been calculated, and the calculatedRaman selection rules have been confirmed by experimental phenomenon. Theroom-temperature Raman scattering spectra of nonpolar a-plane GaN have beenmeasured in surface and edge backscattering geometries, respectively. The frequenciesand linewidths of active modes of each different configuration have been analyzed. Theeffect of Mn and Fe implantation in nonpolar a-plane GaN epilayers has been studied byusing Raman scattering spectra. It is found that implantation increases the static disorderand activates modes that were not allowed by the Raman selection rules. Theroom-temperature Raman scattering spectra of semi-polar GaN have been analyzed, theexplanations based on Raman selection rule for experimental phenomena have beengiven, mixing of A1and E1modes occurs when the incident or the scattered radiation isnot strictly parallel or perpendicular to the c-axis, and the frequency value of thequasi-TO mode has been influenced by the polarizations of the incident and scatteredlight in addition to the angle of propagation with respect to the c-axis.Finally, the influences of three kinds of stress including hydrostatic stress, biaxial stressand uniaxial stress on Raman modes have been discussed. First-order Raman scatteringsof hexagonal polar GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied ina temperature range between303K and503K. The temperature dependences of twoGaN Raman modes (A1(LO) and E2(high)) are obtained. We focus our attention on thetemperature dependence of E2(high) mode, and find that for different types of GaNepilayers their temperature dependences are somewhat different. We compare theirdifferences and give them an explanation. And the simplified formulas we obtained arein good accordance with experiment data. The results can be used to determine thetemperature of a GaN sample.