Carrier extraction from GaSb quantum rings in GaAs solar cells using direct laser excitation

The authors report on the analysis of the hole escape mechanisms from type-II GaSb quantum rings (QRs) embedded within the active region of a GaAs single junction solar cell. When the solar cell is excited by using a 1064 nm infrared laser with excitation energy lower than the bandgap of the GaAs matrix, photogenerated electron??hole pairs are created directly within the GaSb QRs. The QR photocurrent exhibits a linear dependence on the excitation intensity over several decades. The thermal activation energy was found to be weakly dependent on the incident light level and increased by only a few meV over several orders of excitation intensity. The magnitude of the relative absorption in the author??s QRs when directly probed by using a 1064 nm laser with an incident power density of ~ 2.6 W cm^-2??4 per layer. The thermal escape rate of the holes was calculated and found to be ~ 10¹¹ to 10¹² s^??1, which is much faster than the radiative recombination rate 10⁹ s^??1. This behaviour is promising for concentrator solar cell development and has the potential to increase solar cell efficiency under a strong solar concentration.