Study of indium arsenide quantum dots on gallium arsenic antimonide for intermediate band solar cells

InAs/GaAsSb is studied as a promising candidate for intermediate band solar cells (IBSCs). In this dissertation, I focus on fundamental issues for the IBSCs: i) quantum dot (QD) uniformity and density should be optimized to form an intermediate state (IB) and maximize absorption cross-section in QDs, respectively; ii) the occupation of QD electronic states should be controlled for realizing three simultaneous transitions; and iii) valence band offset (VBO) that can cause open circuit voltage loss should be minimized. By addressing these issues it is possible to demonstrate the suitability of InAs/GaAsSb for the IBSCs.;QD uniformity and density in InAs/GaAsSb for increasing Sb content are studied using Atomic Force Microscopy (AFM). AFM results show that QD density and uniformity improve with Sb content increase. The improvement of QD uniformity is ensured by the narrowing of photoluminescence (PL) spectra. Additionally, the PL spectra are compared with the band calculation of the InAs/GaAsSb.;Capacitance-Voltage (C-V) profiling on quantum structures is performed to calibrate delta-doping levels. The occupation of QD electronic levels in InAs/GaAsSb is controlled and determined with the calibrated delta-doping levels. PL spectra of lightly and heavily doped samples show different PL peak positions. This is attributed to carrier population caused by the delta-doping plane. The thermal activation energies and carrier lifetime estimated from Arrhenius fitting curves and time-resolved photoluminescence (TRPL) data, respectively, for lightly and heavily doped samples support the tendency that electrons from the delta-doping plane induce the enhancement of Columbic interaction. The influence of the delta-doping level on carrier behavior in the InAs/GaAsSb is discussed.;To obtain minimum VBO, InAs/GaAsSb with various Sb compositions is investigated by PL and TRPL measurements. PL data shows a blue-shift as excitation power increases as evidence of a type II band structure. Since the PL peak of 8 and 13% Sb samples did not shift while that of 15% Sb sample is blue-shifted with increasing the excitation power it is concluded that InAs QDs/GaAs 0.86Sb0.14 would have minimum valence band offset. This tendency is supported by the change of a carrier lifetime estimated from TRPL data.