Uncooled MWIR InAs/GaSb type-II superlattice grown on a GaAs substrate

Abstract

InAs/GaSb type-II superlattices (T2SLs) are attractive due to their potentially low dark currents and high responsivity. These low dark currents arise due to reduced Auger recombination caused by the spatial separation between the electrons and holes. Coupling these two aspects together leads to the potential of high operating temperature and high D*. An additional attraction of T2SLs is their wavelength tunability; the wavelength can be tuned between 3 to 12 μm, making them attractive for the militarily important MWIR and long-wave infrared (LWIR) bands. InAs/GaSb T2SLs are traditionally grown upon GaSb substrates due to lattice matching of the type-II material on GaSb. However, GaSb substrates are relatively small and expensive compared with GaAs, leading to increased cost. Additionally, the high absorption coefficient of GaSb requires the substrate to be removed prior to use in FPAs. We present an InAs/GaSb T2SL grown upon a GaAs substrate which operates at room temperature. A room temperature spectral response could be measured for the layer, with responsivity and shot and thermal noise limited specific detectivity (D*) of 0.45 A/W and 8.0x108 cmHz1/2/W, respectively, at a bias voltage of -0.3 V. This uncooled operation D* is the best to date compared with the literature for a p-i-n or n-i-p MWIR structure grown upon a GaAs substrate.