Radiation Effects in Thinned GaAs Photovoltaics Incorporating DBRs for Improved Radiation Tolerance of Multijunctions
Stephen J. Polly1, George T. Nelson1, Julia R. D'Rozario1, Rao Tatavarti2, Seth M. Hubbard1
1Rochester Institute of Technology, Rochester, NY, United States
/2MicroLink Devices Inc, Niles, IL, United States

Radiation tolerance of a triple junction solar cell, lattice matched to germanium, can be improved by thinning the GaAs middle junction and maintaining power conversion efficiency through the use of a distributed Bragg reflector and patterned dielectric diffraction grating. Simulations using Sentaurus RSoft show that current density lost through reduction of the GaAs base thickness can be recovered by increasing the optical path length through the device using photonic structures such as a distributed Bragg reflector (DBR). In this paper, the simulation is further compared to experiment focusing on the GaAs middle cell, where prior to growing the diode a conductive DBR is grown epitaxially using MOCVD. Internal and external quantum efficiency, as well as performance under 1-sun illumination, is presented showing nearly complete recovery of performance to optically-thick conditions, while using half the thickness of GaAs absorber. These devices were then exposed to 1 MeV electrons with total doses of 2E14, 5E14, and 1E15 cm-2. Post-radiation results and implications of reduction in minority carrier lifetime will be incorporated into the Sentaurus model and presented.