Explore the correlation between intervalley scattering and phonon bottleneck effect on the hot carrier relaxation in bulk GaSb and InN for hot carrier solar cells

Abstract

Slowed carrier intervalley scattering (IVS) may trap some photo-excited carriers within side valleys and reduce the overall thermalization rate. On the other hand, the thermalization rate could also be significantly retarded within the gamma valley by slowing the Klemens decay due to a large phononic bandgap via the phonon bottleneck effect (PBE). However, the correlation between IVS and PBE on slowing the carrier relaxation rate is still unclear. Herein, high-quality bulk InN and GaSb with similar electronic bandgap but remarkably different phononic structures are studied to clarify the above correlation through picosecond time-resolved photoluminescence. The occurrence of IVS is controlled by using different pump energies at high carrier density (∼1019 cm−3). The relaxations of carriers excited at the band edge just above and far above the side valley threshold are, therefore, studied in GaSb. It shows that the effective hot carrier lifetime (τ1) of GaSb gets significantly extended with higher pump energy mainly due to more carriers being trapped in side valleys through IVS. Nevertheless, the longest τ1 of GaSb is still shorter than the shortest τ1 of InN with a more polar nature and larger phononic bandgap. This implies that PBE plays a more decisive role in retarding Γ valley carrier relaxation than the slowed IVS. It indicates that the large phononic bandgap and Fröhlich coupling constant are keys to the slow thermalization rate if the Fröhlich interaction dominates. If the deformation potential interaction dominates this process, then low side valley threshold energy and the Fröhlich constant determine the reduction of the overall thermalization rate.