We present a model for the spectral external quantum efficiency (EQE) to extract the minority carrier diffusion length (Ln) of a unipolar nBp InAs/GaSb Type-II superlattice (T2SL) mid-wave infrared (MWIR) detector. The detector consists of a 4 μm thick p-doped 10ML InAs/10ML GaSb SL absorber with a 50% cut-off wavelength of 5 μm at 80 K and zero bias. The n-type doped InAs/AlSb SL barrier in the structure was included to reduce the GR dark current. By fitting the experimentally measured EQE data to the theoretically calculated QE based on the solution of the drift-diffusion equation, the p-type absorber was found the have Ln = 10 ± 0.5 μm at 80K, and Ln = 12 ± 0.5 μm at 120K and 150K. We performed the absorption coefficient measurement at different temperatures of interest. Also, we estimated the reduced background concentration and the built-in potential by utilizing a capacitance-voltage measurement technique. We used time-resolved-photoluminescence (TRPL) to determine the lifetime at 80K. With the result of the model and the lifetime measurement, we calculated the diffusion coefficient and the mobility in the T2SL detector at various temperatures. Also, we studied the behavior of different dark current mechanisms by fitting the experimentally measured and simulated dark current density under different operating temperatures and biases.
We report high quantum efficiency (QE) MWIR barrier photodetectors based on the InAs/GaSb/AlSb type II superlattice (T2SL) material system. The nBp design consists of a single unipolar barrier (InAs/AlSb SL) placed between a 4 μm thick p-doped absorber (InAs/GaSb SL) and an n-type contact layer (InAs/GaSb SL). At 80K, the device exhibited a 50% cut-off wavelength of 5 μm, was fully turned-ON at zero bias and the measured QE was 62% (front side illumination with no AR coating) at 4.5 μm with a dark current density of 8.5×10-9 A/cm2 . At 150 K and Vb=50 mV, the 50% cut-off wavelength increased to 5.3 μm and the quantum efficiency (QE) was measured to be 64% at 4.5 μm with a dark current of 1.07×10-4 A/cm2 . The measurements were verified at multiple AFRL laboratories. The results from this device along with the analysis will be presented in this paper.