MOCVD-grown wider-bandgap capping layers in long-wavelength infrared photoconductors

Abstract

The use of MOCVD-grown wider-bandgap as a capping layer for long-wavelength infrared (LWIR) photoconductors has been studied using both theoretical and experimental results. A device model is derived which shows that in the presence of a suitable energy barrier between the infrared absorbing layer and the overlaying passivation layer, the high surface recombination rate which is usually present at the semiconductor/passivant interface is prevented from having a significant effect on device performance. The energy barrier, which repels photogenerated minority carriers from the semiconductor surface, is introduced by employing an n-type wafer which consists of a wider-bandgap capping layer that is grown in situ by MOCVD on an LWIR absorbing layer. The derived model allows the responsivity to be calculated by taking into account surface recombination at both the front and back interfaces, thickness of capping and absorbing layers, recombination at the heterointerface, and variations in equilibrium electron concentration. Calculations show that for an absorbing layer, the optimum capping layer consists of and a thickness of the order of 0.1 to 0.2 .