Light-harvesting for high quantum efficiency in InAs-based InAs/GaAsSb type-II superlattices long wavelength infrared photodetectors

Abstract

Because of the limited absorption coefficient and undesired reflection loss, it has been a challenge to obtain sufficient light absorption for type-II superlattice (T2SL) long wavelength infrared (LWIR) detectors with a thin thickness. Here, we report a greatly enhanced photon absorption by light harvesting in InAs/GaAsSb T2SLs grown on InAs substrates. High quantum efficiencies (QEs) were first observed in a set of InAs/GaAsSb superlattice LWIR photodetectors with different absorption layer thicknesses. Long minority carrier diffusion lengths are also indicated. However, these high QEs are mainly attributed to the large refractive index difference between the n-doped InAs buffer layer and the SL material, which not only improves the optical path length of incident light by multireflection in the SL material but also reduces the surface reflection by dual-layer thin-film interference at some special wavelengths. By further adjusting the doping concentration of the buffer layer, we achieved a LWIR detector with high QE of more than 60% based on InAs/GaAsSb T2SLs with a thin absorption region thickness of 3.55 μm without any antireflection coating. Our result provides an effective strategy for thin-film detectors to boost their photoresponse, especially for materials with low absorption coefficients.