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The bandgap energy of the alloy InAsSb has been studied as 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 bandgap 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=13K. The alloy bandgap 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 bandgap InAsSb to be a candidate material for low-temperature long-wavelength infrared detector applications.

Thick InAsBi layers were grown for photoluminescence (PL) characterization. The As to In overpressure ratio was carefully characterized and adjusted to achieve Bi-droplet-free surfaces. A closed loop feedback system was used to maintain the As overpressure during a 5-h deposition sequence. Despite a high degree of control of the growth parameters, evidence for local phase separation was observed in the PL spectra.

The unintentional background electron population and associated interface and surface conductivity in a heterostructure of InAs 0.58 Sb 0.42 with a bandgap of 0.144 eV and AlInSb was studied with multi-carrier Hall-effect analysis. A free electron bulk concentration at 77 K was found with a density of 2.4 × 10 15 cm −3 and mobility of 140 000 cm 2 V −1 s −1 . A surface electron accumulation layer was observed with a density of 5.5 × 10 11 cm −2 and mobility of 4500 cm 2 V −1 s −1 that is consistent with predictions of surface Fermi level pinning. Another accumulation layer was identified at the interface with the AlInSb of 4 × 10 11 cm −2 with a mobility of 37 000 cm 2 V −1 s −1 . The origin of the defects and the implications for device structures are discussed.

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