Effect of deposited passivation materials and doping on recombination at III-V surfaces

Passivation of dangling bonds at surfaces and interfaces is an essential feature of high-efficiency solar cells. The high recombination activity of surface states in III-V semiconductors typically requires epitaxial growth of high-bandgap layers to suppress interface recombination. Surface recombination in III-Vs can be reduced by solution deposition of sulfides, however, the resulting passivation can degrade over time, and surface roughness caused by the passivation can degrade cell performance. In this work, the effects of different passivation materials and techniques, such as atomic layer deposition (ALD) and plasma enhanced chemical vapor deposition (PECVD), on GaAs and InP surfaces are analyzed by direct measurement of the minority-carrier lifetime by time-resolved photoluminescence (TRPL). Recombination parameters due to passivation of surface states are characterized for Al2O3, amorphous silicon (a-Si) and sulfide interfaces on n-type, intrinsic, and p-type GaAs and InP substrates. Al2O3 passivation of n-GaAs has shown 1.35 ns improvement in measured lifetime, while a-Si passivation shows a slight improvement in passivation for n-type GaAs and p-type InP.