Phonons on Quantum Epitaxial Structures Based on Wide Band Gap Materials

摘要

Raman scattering studies were performed on III-V Nitride materials including binary crystals, ternary alloys, and superlattices of GaN/AIN and GaN/ AlGaN. Our results show that in AlGaN alloys the asymmetric behavior of the E2 lineshape arises from random disorder; the E2 phonon does not follow a one mode behavior and the AlGaN films on SiC are under small tensile stress. In the InGaN too the Al mode shows a one mode behavior while two mode behavior may be possible for E2. Possible mode mixing takes place. Evidence of inhomogeneities and spinodal decomposition is seen in these films. Phonon lifetime measurements are made in the binary crystals and in every case we see evidence of two lifetime regions. in the superlattices we see anomalous low temperature behavior that is consistent with a density of states of spectral distribution that is due to the roughness of the interfaces and which agrees with TEM measurements. Finally preliminary measurements demonstrate strong interface phonons in the GaN/AIN superlattices which give good agreement with theory.