Investigation of Quantum Efficiency in Mid-Wave Infrared (MWIR) InAs/GaSb Type-II Strained Layer Superlattice (T2SL) Detectors

The objective of this study is to optimize the absorption in the active region of InAs/GaSb T2SL photodetectors for the realization of high-performance MWIR devices. Two sets of MWIR (lambda(100% cut-off) similar to 5.5 mu m at 77K) T2SL detectors were realized; one set with varied detector absorber thickness, the other set with varied T2SL period. The T2SL material quality was evaluated on the basis of room temperature photoluminescence (RTPL) and the high-resolution X-ray diffraction (HRXRD) data. Then the device performance was compared using spectral response, dark current and responsivity measurements. Finally, quantum efficiency was calculated and employed as a metric for the definition of the optimal T2SL period and active region thickness. For the first part of the study, a homojunction pin architecture based on 8 monolayers (MLs) InAs/8MLs GaSb T2SL was used. The thickness of the non-intentionally doped absorber layers were 1.5 mu m, 2.5 mu m, and 3.5 mu m. For the second part of the study, unipolar barrier (pBiBn) devices were grown. The thickness of the absorber region and the T2SL constituent InAs layer thicknesses were kept the same (1.5 mu m and 8 MLs, respectively) whereas the T2SL constituent GaSb thickness was varied as 6 MLs, 8 MLs, and 10 MLs. We have found that the pin detector with 2.5 mu m thick absorber and the pBiBn detector with 8 ML InAs/8 ML GaSb T2SL composition are, within the scope of this study, optimal for the realization of MWIR single-element devices and FPAs with corresponding architectures.