Title: Temperature-dependent behavior of InAsSb and InAs/GaSb strained layer superlattice infared photodetectors

The development of uncooled infrared (IR) detectors operating in the mid-wave IR (MWIR, 3-5 μm) and long-wave IR (LWIR, 8-12 μm) ranges is important for a variety of potential applications. Present IR technology dominating in this wavelength range is mercury-cadmium-telluride (MCT) detectors characterized by large tunneling currents and sensitivity to variation of composition. InAs/GaSb Type II strain-layer superlattices (SLS) and InAsSb bulk material are good candidates for the development of room temperature detectors. SLSs are characterized by larger electron effective mass (~0.04m
₀
) which leads to a reduction of tunneling currents and lower sensitivity to compositional non-uniformities. InAs
_1-x
Sb
_x
also provides band engineering flexibility due to the availability of lattice matched semiconductors with various band offsets. In addition, InAs
_1-x
Sb
_x
offers the advantage of higher electron and hole mobilities compared to MCT alloys. Most of the InAs/GaSb SLS and InAsSb detectors reported so far are based on the p-i-n design. One of the major dark current components in these devices is Shockley-Read-Hall (SRH) generation-recombination current associated with the depletion region of the p-i-n diode. The recently proposed nBn heterostructure design excludes the SRH component of dark current, since the nBn structure is intended to operate with n-type layers in the flatband with little depletion. Thus, the nBn design allows detector operation limited by diffusion noise current that comes from the generation of minority carriers in extrinsic regions of the photodiode, which then diffuse into the depletion region. The nBn device is designed to have a better performance at the same operational temperature (Figure 1(a)) or to operate at higher temperature with performance comparable to the PIN diode (Figure 1 (b)). As was shown by Klipstein [1], in order to verify diffusion limited behavior of the nBn detector over a wide range of operation temperatures, value of zero temperature bandgap Eo have to be measured. Eo can be extracted from linear-quadratic relation proposed by Varshni, if variation of material bandgap with temperature is known. We investigated the temperature-dependent behavior of MWIR, LWIR and dual-color (MWIR/LWIR) detectors based on bulk InAsSb and InAs/GaSb SLS with p-i-n and nBn designs with conventional absorption, photoluminescence and spectral response techniques. Figures 2 and 3 show Varshni fits for detectors with nBn and pin designs, respectively, operating in MWIR and LWIR spectral regions. The symbols correspond to the values of the energy bandgap measured at each given temperature. Then values of Varshni parameters, zero temperature bandgap E
₀
and empirical coefficient a, were extracted. Support fromAFOSR grant FA9550-10-1-0113 is gratefully acknowledged.