/ InP Core-Shell Nanowires with Type II Band Alignment*

Time-resolved optical measurements of single zinc-blende GaAs_0.7Sb_0.3 core-only and GaAs_0.7Sb_0.3/InP core-shell nanowires at 10K are obtained from pump-probe measurements. The core-shell nanowires exhibit a remarkably longer lifetime (≈ 600 times) compared with core-only nanowires. Measurements at 300K show only a factor of 6 enhancement. These results suggest that band alignment of the core-shell nanowire may be Type II with less than a 30meV off-set. Carrier thermalization and carrier density evolution obtained from fitting the nanowire spectra using Transient Rayleigh scattering (TRS) modeling provide supporting evidence for Type II band alignment. By modeling the energy loss mechanism of carriers based on longitudinal optical and acoustic phonon emission, we are able to simulate carrier thermalization. These results show that at early times optical phonon emission dominates the carrier energy loss rate. For core-shell nanowires at 10 K, the acoustic phonon emission dominates after 300 ps.