Recombination processes in gallium indium arsenic antimonide and indium gallium arsenide materials for thermophotovoltaic applications.

摘要

Recent improvements in the quality of epitaxial growth of low-bandgap III-V semiconductors opened new horizons for thermophotovoltaic (TPV) technology. Current developments of TPV energy converters, optimized for thermal sources heated to ∼1000°C, are based on GaInAsSb and InGaAs material systems with cut-off wavelength range of 2.1--2.5 mum. As for any minority carrier device, bulk and interface recombination is a key factor affecting TPV cell performance.; This thesis presents analysis of recombination processes in GaInAsSb and InGaAs alloys grown on GaSb and InP substrates, respectively, by organometallic vapor-phase epitaxy (OMVPE). Minority carrier lifetime was experimentally studied using three complementary techniques. Time-resolved photoluminescence (TRPL) setup based on the state-of-art fast-response mid-infrared photodiodes was designed to explore transient PL dynamic. Static recombination lifetime was extracted from modulation bandwidth of PL under small-signal periodical excitation. Fast relaxation processes were studied using wavelength up-conversion photon counting system based on periodically-poled lithium niobate (PPLN) crystal for efficient nonlinear mixing.; It was found that accumulation of electrons at the p-GaInAsSb/GaSb type-II interface contributes significantly to the recombination velocity S. The use of heavily p-doped GaSb cap layers was proposed to eliminate the potential well for electrons at the interface. Increasing the GaSb cap doping level resulted in threefold reduction of S. Record value of recombination velocity at GaInAsSb/AlGaAsSb heterointerface of 30 cm/s was demonstrated. Radiative and Auger recombination coefficients were determined by measuring a series of GaInAsSb structures with varied thickness and doping concentrations. Effect of dopant type on recombination kinetics in InGaAs was studied for the first time. It was shown that Zn-doped InGaAs demonstrated intensity-dependant carrier lifetime while linear recombination mode is typical for Te-doped material. This phenomenon can be attributed to the saturation of deep donor-like recombination centers.; The obtained results provide insight into recombination properties of thermophotovoltaic materials, which is essential for the further device optimization.