Significant photodiode quantum efficiency improvement and spectral response alteration through surface effects in vacuum

Two commercial photodiodes are investigated for quantum efficiency improvement in a vacuum environment. Surface effects stemming simply from photodiode operation in such an environment are shown to significantly improve quantum efficiency. This is attributed to desorption of surface impurities and consequent reduction of surface recombination and Debye length. An abrupt-junction device is shown to exhibit increased depletion layer width in vacuum. Spectral dependence of quantum efficiency improvement in vacuum favors detection at longer wavelengths. This is attributed to surface Debye length decrease in vacuum, which implies that the surface recombination volume decreases for longer wavelengths.