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.

GaSb-based type-I quantum-well diode lasers emitting at 3.36 m at 12°C with 15 mW of continuous wave output power are reported. Devices with two or four InGaAsSb compressively strained quantum wells and AlInGaAsSb quinternary barriers were fabricated and characterized. It was shown that increase in the quantum-well number led to improved laser differential gain and reduced threshold current.The growing demand for light emitters capable of high power room temperature operation in spectral region from 3 to 3.5 m encourages intensive search for appropriate design approach to fabricating such photonic devices. Both monopolar and bipolar lasers based on cascade and multiple quantum well ͑QW͒ active region designs are being extensively researched for this purpose ͑see, for instance, Refs. 1 and 2͒. GaSb-based type-I QW diode lasers operate in continuous wave ͑cw͒ at room temperature in spectral region above 3 m. 3,4 Diode lasers grown by molecular beam epitaxy on GaSb substrates and operating up to 3.1 m at room temperature in cw mode have been recently reported by our group. 5 Further increase in the operating wavelength of type-I QW GaSb-based lasers faces two major complications ͑a͒ gradual decrease in the valence band offset between InGaAsSb QW and Al containing barrier layers when In and As concentrations in QW are increased 6 and ͑b͒ possible increase in the nonradiative Auger recombination rate when QW bandgap decreases. The latter is thought to be fundamental in nature.The lack of valence band offset in GaSb-based heterostructures can be overcome by introduction of heavy compressive strain above 1% into InGaAsSb QWs 7 and utilization of the quinternary AlInGaAsSb barrier material. 4,8 The contribution of the Auger recombination processes to threshold current can be minimized by a reduction in the threshold carrier concentration through improvement of the hole confinement itself and by increase in the number of QWs in device active region.In this work we report on the development of the 3.36 m emitting lasers with strained active region and quinternary barrier material. We demonstrate that increase in the number of QWs from two to four decreases the device threshold current through improvement in the laser differential gain ͑with respect to current͒. Diode lasers with four QW active regions operate in cw mode at 12°C with 15 mW of output power at 3.36 m.Laser heterostructures were grown at State University of New York at Stony Brook by solid-source molecular beam epitaxy using Veeco GEN-930 reactor equipped with As and Sb valved cracker sources. Te and Be were used for nand p-doping, respectively. Laser active region contained either two or four 16 nm wide 1.5% compressively strained InGaAsSb QWs with nominal In composition of 54%. The interwell spacings were 40 and 20 nm in two-QW and four-QW devices, respectively. The waveguide ͑total width of 1 m͒ and barrier materials were Al 0.20 In 0.25 Ga 0.55 As 0.26 Sb 0.74 . The cladding material was Al 0.9 Ga 0.1 As 0.07 Sb 0.93 . Graded bandgap heavily doped transiti...

Cascade GaSb-based type-I quantum well diode lasers were designed and fabricated. Cascade pumping was achieved utilizing efficient interband tunneling through "leaky" window in band alignment at GaSb/InAs heterointerface. The carrier recycling between stages was confirmed by twofold increase of the slope efficiency in two-stage devices as compared to reference single-stage lasers. Moderate internal optical loss increase was observed in cascade lasers with interband injector located near the optical mode peak. Cascade pumping scheme increased the continuous wave output power of room temperature operated 3 μm semiconductor lasers up to 590 mW and led to improved power conversion efficiency.

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Mid-IR ͑ Ϸ 3-3.5 m͒ light emitting diodes with quinternary AlInGaAsSb barriers and InGaAsSb strained quantum wells grown on GaSb substrates have been demonstrated. The devices produced a quasi-cw emission power of 0.7 mW at room temperature and 2.5 mW at T =80 K.

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.

We have performed time-resolved measurements of the far-infrared photoresponse of two-dimensional electron systems in the quantum Hall regime. The photoresponse consists of two equally important components: the longitudinal component, caused by the photoinduced change of the longitudinal resistance Rxx, and the transversal component, caused by the photoinduced Hall currents and by the photoinduced change of Rxy. Both these components are connected with two mechanisms of the photoresponse: a nonresonant bolometric, and a cyclotron-resonant contribution.

Quasiparticles with Dirac-type dispersion can be observed in nearly gapless bulk semiconductors alloys in which the bandgap is controlled through the material composition. We demonstrate that the Dirac dispersion can be realized in short-period InAsSb/InAsSb metamorphic superlattices with the bandgap tuned to zero by adjusting the superlattice period and layer strain. The new material has anisotropic carrier dispersion: the carrier energy associated with the in-plane motion is proportional to the wave vector and characterized by the Fermi velocity v, and the dispersion corresponding to the motion in the growth direction is quadratic. Experimental estimate of the Fermi velocity gives v = 6.7 × 10 m/s. Remarkably, the Fermi velocity in this system can be controlled by varying the overlap between electron and hole states in the superlattice. Extreme design flexibility makes the short-period metamorphic InAsSb/InAsSb superlattice a new prospective platform for studying the effects of charge-carrier chirality and topologically nontrivial states in structures with the inverted bandgaps.