The band gap energy of the alloy InAsSb has been studied as a function of composition with special emphasis on minimization of strain-induced artifacts. The films were grown by molecular beam epitaxy on GaSb substrates with compositionally graded buffer layers that were designed to produce strain-free films. The compositions were precisely determined by high-resolution x-ray diffraction. Evidence for weak, long-range, group-V ordering was detected in materials exhibiting residual strain and relaxation. In contrast, unstrained films having the nondistorted cubic form showed no evidence of group-V ordering. The photoluminescence (PL) peak positions therefore corresponds to the inherent band gap of unstrained, unrelaxed, InAsSb. PL peaks were recorded for compositions up to 46$\%$ Sb, reaching a peak wavelength of 10.3 μm, observed under low excitation at $T=13$ K. The alloy band gap energies determined from PL maxima are described with a bowing parameter of 0.87 eV, which is significantly larger than measured for InAsSb in earlier work. The sufficiently large bowing parameter and the ability to grow the alloys without ordering allows direct band gap InAsSb to be a candidate material for low-temperature long-wavelength infrared detector applications.

The absorption spectra for the antimonide-based type-II superlattices (SLs) for detection in the long-wave infrared (LWIR) are calculated and compared to the measured data for SLs and bulk materials with the same energy gap (HgCdTe and InAsSb). We include the results for the metamorphic InAsSb_x/InAsSb_y SLs with small periods as well as the more conventional strain-balanced InAs/Ga(In)Sb and InAs/InAsSb SLs on GaSb substrates. The absorption strength in small-period metamorphic SLs is similar to the bulk materials, while the SLs with an average lattice constant matched to GaSb have significantly lower absorption. This is because the electron-hole overlap in the strain-balanced type-II LWIR SLs occurs primarily in the hole well, which constitutes a relatively small fraction of the total thickness.

The electronic properties of unstrained unrelaxed InAs _x Sb_1−x alloys have been determined in a wide range of alloy compositions using IR magnetospectroscopy, magnetotransport and IR photoluminescence. All studied alloys have n-type background doping with electron concentration decreasing with the Sb content. The composition dependence of the background doping concentration follows an empirical exponential law in a wide range of compositions. Both bandgap and electron effective mass dependence on alloy composition exhibit negative bowing reaching lowest values at x = 0.63: E _g = 0.10 eV, m* = 0.0082 m ₀ at 4.2 K. The bowing coefficient of 0.038 m ₀ obtained for the electron effective mass is in good agreement with that obtained from the Kane model.

InAs_0.6Sb_0.4/Al_0.75In_0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga_1−xIn_xSb buffer layers and GaSb substrates by molecular beam epitaxy. At the wavelength of 8 μm and T = 150 K, devices with 1-μm thick absorbers demonstrated an external quantum efficiency of 18% under a bias voltage of 0.45 V.

Metamorphic heterostructures containing bulk InAs_1−xSb_x layers and AlInAsSb barriers were grown on GaSb substrates. The lattice mismatch (up to 2.1%) between the GaSb substrates and the InAsSb layers was accommodated by the growth of GaInSb linearly graded buffers. The 1 μm thick InAsSb_0.44 layer with an absorption edge above 9 μm exhibited an in-plane residual strain of about 0.08%. InAs_1−xSb_x structures with x = 0.2 and x = 0.44 operated as light emitting diodes at 80 K demonstrated output powers of 90 μW and 8 μW at 5 μm and 8 μm, respectively.