Effects of 63 MeV proton-irradiation on the dark-current in III-V-based, unipolar barrier infrared detectors

Abstract Recent investigations demonstrated that III-V-based nBn infrared detectors typically experience relatively significant performance degradation under 63 MeV proton irradiation due to displacement damage, limiting their viability for certain space-based applications. Additionally, the investigations suggested, based on simplified expressions, that the nBn’s diffusion-limited dark-current would transition from a linear-dependence on proton fluence to a square-root-dependence as the minority carrier recombination lifetime decreased and the subsequently decreasing diffusion length became less than the thickness of the detector’s quasi-neutral absorbing region. Here, a closer examination of this expected behavior is reported on. Evidence from multiple nBn detector rad-tolerance experiments and simple numerical simulations indicated the behavior of the nBn’s diffusion-current under proton irradiation can be more complicated than was previously suggested. For example, in some nBn detectors proton irradiation was observed to increase the doping density of the absorber sufficient to impact the diffusion-current and lessen its power-law-dependence on the proton fluence. This increase was confirmed by analysis of in situ capacitance–voltage measurements on an irradiated nBn detector, which found an n-type carrier addition rate ∼ 140  cm −1 . Simulations showed this level of carrier addition can lead to a ∼ 75 % reduction in the expected diffusion-current density for an equivalent dose of 100 krad(Si). Simulations also showed the nBn diffusion-current’s instantaneous power law-dependence on proton fluence peaked well below unity and then began approaching −.5 rather than.5, which was suggested by those previous investigation. A high native defect density prior to irradiation and finite surface recombination velocity were both found to reduce the initial power-law dependence and shift its peak position.