Minority carrier lifetime and interband absorption in midinfrared range of spectra were measured in InAs/GaSb strained-layer superlattices ͑SLSs͒ grown by molecular beam epitaxy on GaSb substrates. The carrier lifetime in 200-period undoped 7 ML InAs/8 ML GaSb SLS with AlSb carrier confinement layers was determined by time-resolved photoluminescence ͑PL͒ and from analysis of PL response to sinwave-modulated excitation. Study of PL kinetics in frequency domain allowed for direct lifetime measurements with the excess carrier concentration level of 3.5ϫ 10 15 cm −3. The minority carrier lifetime of 80 ns at T = 77 K was obtained from dependence of the carrier lifetime on excitation power.

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Minority carrier lifetime, τ, in type-2 strained-layer superlattices (SLSs) and in long-wave Hg0.78Cd0.22Te (MCT) was measured by optical modulation response technique. It was shown that at 77 K radiative recombination can contribute to the measured τ values. The Shockley–Read–Hall (SRH) lifetimes were attained as 100 ns, 31 ns, and more than 1 μs for midwave infrared superlattices, long-wave infrared (LWIR) superlattices, and MCT correspondingly. The nature of the difference between the SRH lifetimes in LWIR superlattice and MCT is discussed.

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.

Minority carrier lifetimes in 0.55 eV band-gap GaInAsSb epitaxial layers that are double capped with GaSb or AlGaAsSb layers were determined using time-resolved photoluminescence. It was found that accumulation of electrons at the p-doped GaInAsSb/GaSb type-II interface contributes significantly to the interfacial recombination velocity S, which was measured to be 3100 cm/s. The use of heavily p-doped GaSb cap layers was proposed to eliminate the potential well of electrons and barrier for holes at the interface. Increasing the GaSb cap doping level from 1ϫ10 16 to 2 ϫ10 18 cm Ϫ3 resulted in a 2.7 times reduction of S down to 1140 cm/s. The smallest value of S was determined to be 720 cm/s, which was obtained for structures with AlGaAsSb cap layers that have no valence band offset.

Unrelaxed InAs1−xSbx layers with lattice constants up to 2.1% larger than that of GaSb substrates were grown by molecular beam epitaxy on GaInSb and AlGaInSb compositionally graded buffer layers. The topmost section of the buffers was unrelaxed but strained. The in-plane lattice constant of the top buffer layer was grown to be equal to the lattice constant of unrelaxed and unstrained InAs1−xSbx with given X. The InAs0.56Sb0.44 layers demonstrate photoluminescence peak at 9.4 μm at 150 K. The minority carrier lifetime measured at 77 K for InAs0.8Sb0.2 was τ = 250 ns.

The authors demonstrate a double quantum well GaSb-based diode laser operating at 2.4μm with a room-temperature cw output power of 1050mW and a maximum power-conversion efficiency of 17.5%. Laser differential gain with respect to current increases by a factor of 2 and laser threshold current is nearly halved when the compressive strain in the quantum wells is increased from 1.2% to 1.6%. This improvement is due to substantially improved hole confinement in the heavily compressively strained active region.

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.