Crystal phase induced bandgap modifications in AlAs nanowires probed by resonant Raman scpectroscopy

We report on a major modification of the fundamental electronic band structure of AlAs when grown as a nanoscaled wurtzite crystal. Resonant Raman spectra of individual AlAs GaAs core shell nanowires display a resonance between 1.83 and 2.18 eV for the AIAs E-1(TO) phonon mode. Our findings substantiate the lowest conduction band of wuruite AIAs to comprise Gamma(8) symmetry and a low effective mass in agreement with calculations reported recently. The electronic resonance falls below the X, Land Gamma valleys known for AlAs in the zincblende phase. This result points toward a direct nature of wurtzite AIM and is expected to apply more generally to semiconductors that in the bulk phase exhibit L valleys at lower energies than the conduction band at the Gamma point.