Rapid thermal annealing of InAlAsSb lattice-matched to InP for top cell applications

The effect of rapid thermal annealing on the optical properties of In_xAl_1-xAs _ySb _1-y was analyzed and compared to that for In_0.52 Al_0.48As. Initial ellipsometry and photoluminescence experiments performed before the annealing indicate the presence of a low energy Urbach tail in the absorption spectrum. Rapid thermal annealing produces a blue-shift in the PL emission when annealed at 650°C for 60s and a decrease in the full-width-half-maximum, which originates from a reduction of the emission from the longer wavelength states. For the In_0.52 Al_0.48As, the emission energy and the full-width-half-maximum remain constant during the annealing study. The elimination of sub-bandgap states in In_0.52 Al_0.48As is critical for achieving a realistic path towards high efficiency multijunction cells lattice-matched to InP.