ZnSe window layers for GaAs solar cells

We examine ZnSe as a potential window-layer material for GaAs. ZnSe is nearly lattice-matched to GaAs, as well as to GaInP, and has a bandgap of 2.67 eV, which is significantly higher than that of AlGaAs. If good surface passivation of the GaAs by ZnSe can be achieved, a significant improvement in short-circuit current (and hence efficiency) should be possible. We have characterized n-type ZnSe deposited by OMCVD on GaAs for a variety of growth conditions and doping levels. An 80-nm thick n-ZnSe film deposited on epitaxial n-GaAs leads to a fivefold increase in photoluminescence (PL) intensity compared to a bare sample, indicating reduced surface recombination (SRV). The wavelength dependence of the backside PL signal is approximately constant for the ZnSe-coated sample, while it increases with wavelength for the bare wafer. This also indicates a significant reduction in SRV.