GaSb Solar Cells Grown by MOCVD via IMF on GaAs
Stephen J. Polly, Emily S. Kessler-Lewis, George T. Nelson, Seth M. Hubbard
Rochester Institute of Technology, Rochester, NY, United States

The use of antimonides is discussed as path to multijunction photovoltaics with optimal bandgap current matching, alternative to designs based around the Ge lattice constant or incorporating thick metamorphic gradings and buffer layers. This is achievable through direct growth of GaSb onto GaAs substrates. The large lattice mismatch between GaAs and GaSb (7.8%) is used to induce an interfacial misfit array, locking 90° dislocations in a thin layer which do not propagate in the growth direction. This method allows for direct heterepitaxy of GaSb and related direct bandgap materials on GaAs and InGaP2 heritage device structures without the need for a thick grading buffer, enabling a wider range of more cost effective inverted multijunction photovoltaic devices. Solar cells were grown by MOCVD and fabricated to investigate the growth of GaSb single junction solar cells on GaAs substrates using the IMF technique as a function of growth conditions including metalaorganic precursor type and layer design. Device results including 1-sun light-IV, quantum efficiency, and minority carrier lifetime will be discussed and compared against GaSb homoepitaxial devices, showing IMF devices with 2.0% AM1.5G efficiency, and improvement over previous results by MBE. This result, used as one input to a physics-based simulation of a multijunction InGaP2/GaAs tandem, shows an efficiency increase of 1% absolute.