Impact of annealing and V:III ratio on properties of MBE grown wide-bandgap AlGaInP materials and solar cells

The growth and properties of wide bandgap (Al_xGa_1-x)_0.51In_0.49P layers and solar cells grown by solid source molecular beam epitaxy were examined to correlate the impact of growth conditions and in-situ annealing on photovoltaic performance. A P₂:III flux ratio of 12 was found to optimize the optical qualities of Ga_0.51In_0.49P epilayers. Ga_0.51In_0.49P solar cells were grown and subjected to different in-situ annealing conditions. The effect of annealing on material quality and device performance was characterized through deep level transient spectroscopy (DLTS) and photoluminescence (PL), which revealed a trend in non-radiative recombination. The results suggest that removal of a deep level near E_C - 0.78 eV in the n-type base is responsible for the observed improvement in current collection seen after anneal. After refinement of the Ga_0.51In_0.49P growth, wider bandgap material was investigated for future use in a high temperature/high intensity solar cell. A range of (Al_xGa_1-x)_0.51In_0.49P materials, with direct bandgaps from 2.09 eV to 2.26 eV have been successfully demonstrated using digital alloying and conventional bulk growth.