Carrier Recombination and Surface Band Bending in GaAs/InGaAs Core-Shell Nanowires with Reverse Type-I Band Alignment

GaAs/In_xGa_1-xAs core-shell nanowires (NWs) with reverse type-I band alignment have attracted significant interest in optoelectronics due to their unique optical properties. However, the detailed characterizations of carrier recombination in these NWs remain insufficiently explored. In this study, GaAs/In_0.3Ga_0.7As core-shell NWs were grown via molecular beam epitaxy, and their optical properties were investigated by optical spectroscopies. For GaAs/In_0.3Ga_0.7As core-shell NWs with an 80 nm core and a 30 nm shell, the bandgap of the InGaAs shell was found to be significantly reduced by approximately 0.93 eV due to compressive strain. Power-dependent photoluminescence measurement revealed a direct transition near the band edge in the shell as well as an indirect transition associated with surface states. With an increase in temperature, the Fermi level shifts closer to the valence band, leading to band bending and a reduction in the depletion region. When the temperature exceeds 180 K, the surface-trapped carriers overcome the potential barrier, resulting in an increase in the number of direct transitions. Our results demonstrate that GaAs/InGaAs core-shell NWs with reverse type-I band alignment exhibit a strong potential for efficient photogenerated carrier extraction and collection, making them promising candidates for a wide range of optoelectronic applications.