Device implications of phonons in III-IV nitride bulk and dimensionally confined semiconductors

Fundamental properties of phonons in bulk and dimensionally confined III-nitrides are examined with a view toward understanding processes important in the operation of semiconductor devices.{09}The optical phonons in wurzite III-nitrides are examined experimentally in ternary and quaternary thin films and dimensionally confined AlN/GaN superlattice and self-assembled GaN quantum dot structures. Dimensional confinement effects on the optical phonon dispersion behavior are presented and experimental results will be discussed. Results of mid and deep-UV Raman spectroscopy of ternary In xGa1-xN and quaternary AlxGa1-x-yIn yN thin films grown on (0001) sapphire substrates grown by metal-organic chemical vapor deposition (MOCVD) are analyzed. Raman scattering results for binary superlattices of AlN/GaN with excitation energies of 325 nm and 244 nm are also reported. Lastly, self-assembled GaN quantum dots grown by plasma-assisted molecular beam epitaxy with island density controlled in the Stranski-Krastanov mode are characterized using Raman techniques. The strain-induced frequency shifts observed with Raman measurements are compared with modeled predictions and discussed. Additional interesting results gained through Raman and Photoluminescence will be presented including: Raman experimental results suggesting the presence of compositional inhomogeneities and spinodal decomposition in the thin InGaN films, and photoluminescence data for binary superlattices and self-assembled GaN quantum dots demonstrating the extremely strong spontaneous and piezoelectric fields present in the wurzite GaN material system and their dramatic effect on the observed luminescence. The total internal electric field in the AlN/GaN SL is estimated from the experimental observations and discussed.