Bulk InAsxSb1-x nBn photodetectors with greater than 5μm cutoff on GaSb

Mid-wavelength infrared nBn photodetectors based on bulk InAsxSb1-x absorbers with a greater than 5 μm cutoff grown on GaSb substrates are demonstrated. The extended cutoff was achieved by increasing the lattice constant of the substrate from 6.09 to 6.13 A using a 1.5 μm thick AlSb buffer layer to enable the growth of bulk InAs0.81Sb0.19 absorber material. Transitioning the lattice to 6.13 A also enables the use of a simple binary AlSb layer as a unipolar barrier to block majority carrier electrons and reduce dark current noise. Individual test devices with 4 μm thick absorbers displayed 150 K dark current density, cutoff wavelength, and quantum efficiency of 3 × 10−5 A/cm2, 5.31 μm, and 44% at 3.4 μm, respectively. The instantaneous dark current activation energy at a given bias and temperature is determined via Arrhenius analysis from the Dark current vs. temperature and bias data, and a discussion of valence band alignment between the InAsxSb1-x absorber and AlSb barrier layers is presented.