Carrier transport in nBn infrared detectors

Abstract

The nBn photodetector architecture proposed and demonstrated by Maimon and Wicks provides an effective means for lowering generation-recombination dark current by suppressing Shockley-Read-Hall processes, and for reducing surface leakage dark current. This has been especially beneficial for III-V semiconductor based infrared photodiodes, which traditionally tend to suffer from excess depletion dark current and lack of good surface passivation. We examine how contact (n), barrier (B), and absorber (n) properties can affect carrier transport in nBn infrared detector. In an nBn detector the unipolar electron barrier should block only the electrons while allowing the un-impeded flow of holes, but improper barrier doping or barrier-absorber band offset could also block hole transport and result in higher turn-on bias. Contact doping has also been observed to result in higher turn-on bias at higher temperatures. In the case when the absorber is made from n-doped type-II superlattice (T2SL), although it is often assumed that the exceedingly large growth-direction band-edge curvature hole effective mass in n-type long-wavelength infrared (LWIR) T2SL would lead to low hole mobility and therefore low detector collection quantum efficiency, in practice mid-wavelength infrared (MWIR) and LWIR nBn infrared detectors have demonstrated good optical response. We explore how hole mobility can be affected by band structure effects such as band mixing and subband splitting to gain better understanding of hole transport in T2SL.