Atomic layer deposited passivation layers for superlattice photodetectors

The authors report on the effects of atomic layer deposited Al2O3, TiO2, HfO2, and ZnO layers as a passivation material for type-II InAs/GaSb superlattice midwave infrared photodetectors. Low temperature and plasma free operation with defect free and conformal coating of the atomic layer deposition technique creates an efficient passivation layer. In this study, photodiodes coated with and without passivation layer were compared for their dark current and surface resistivity performances. For Al2O3 coated diodes, the dark current density was improved by more than two orders of magnitude at 77K under -50 mV bias. As a result, HfO2 and TiO2 passivated diodes are better than reference diodes, but they are not as good as Al2O3 passivated diodes. Low Gibbs free energy of the aluminum oxides helps eliminating conductive native surface oxides in a self cleaning process. (C) 2014 American Vacuum Society.