Room-temperature pump–probe transmission experiments have been performed on an arsenic-rich InAs/InAs1−xSbx strained layer superlattice (SLS) above the fundamental absorption edge near 10 μm, using a ps far-infrared free-electron laser. Measurements show complete bleaching at the excitation frequency, with recovery times which are found to be strongly dependent on the pump photon energy. At high excited carrier densities, corresponding to high photon energy and interband absorption coefficient, the recombination is dominated by Auger processes. A direct comparison with identical measurements on epilayers of InSb, of comparable room-temperature band gap, shows that the Auger processes have been substantially suppressed in the superlattice case as a result of both the quantum confinement and strain splittings in the SLS structure. In the nondegenerate regime, where the Auger lifetime scales as τ−1aug=C1N2e, a value of C1 some 100 times smaller is obtained for the SLS structure. The results have been interpreted in terms of an 8×8 k⋅p SLS energy band calculation, including the full dispersion for both k in plane and k parallel to the growth direction. This is the strongest example of room-temperature Auger suppression observed to date for these long-wavelength SLS alloy compositions and implies that these SLS materials may be attractive for applications as room-temperature mid-IR diode lasers.

Room-temperature InAs/InAs1−xSbx strained-layer superlattice light-emitting diodes (x∼8%) are reported that emit at λ∼4.2 μm with an internal efficiency of 2.8%. The structures are grown by molecular beam epitaxy on slightly mismatched InAs substrates and include a strained AlSb barrier layer to prevent electron migration to the dislocated substrate–epilayer interface region. Comparison with a near identical structure grown without the barrier layer indicates a factor of four improvement in device efficiency at room temperature.

Impact of substrate temperature on the structural and optical properties of strain-balanced InAs/InAsSb type-II superlattices grown by molecular beam epitaxy

Arsenic-rich InAs/lnAsr-,Sbx strained layer superlattices (SLSs) grown on GaAs substrates by molecular beam epitaxy (MBE) are studied for their potential application as infrared emitters. The long-wavelength emission (4-1 1 pm) is highly sensitive to superlattice design parameters and is accounted for by a large type4 band offset, greater than in previously studied antimony-rich InSb/lnAs,_,Sb, SLSs. High internal PL efficiencies (>lo%) and intense luminescence emission were observed at these long wavelengths despite large dislocation densities. Initial unoptimized InAs/lnAsr_,Sb, SLS light emitting diodes gave ss200 nW of A = 5 pm emission at 300 K.In(AsSb) strained layer superlattices (SLSs) offer infrared detector and emitter applications beyond IO p m , Although mid-infrared lead salt lasers already exist they suffer from thermal conductivity, doping and metallurgical problems which have restricted their operation to temperatures below 200 K [l]. In(AsSb) offers superior metallurgical stability and compatibility with existing II-V technology compared to other infrared materials like cadmium mercury telluride. To date, because of the narrow bandgaps of the alloy constituents, InSb/InAsl-,Sb, SLSs composed of Sb-rich alloys have mainly been studied for long-wavelengh (510 pm) applications, notably longwavelength photodiodes [2]. The 10 pm response of the latter arises from the type-I1 band offset which gives a superlattice structure with an effective bandgap lower than either of the alloy constituents.The lack of lattice matched substrates, however, leads to defect densities of the order of (1-3) x IO9 cm-* (largely independent of alloy composition) in the active region of the device [3]. These give rise to Shockley-Read generation-recombination centres which limit the detectivity and emission efficiencies of Sb-rich alloy optoelectronic devices. In contrast, Walukiewicz [4] has shown that InAs is unique among the m-Vs in that pointlike lattice defects produce electronic states above the conduction band edge as opposed to in the forbidden gap.

The band alignments and band offsets were investigated for In͑As,Sb͒/InAs superlattices of various periods and compositions. Magnetoabsorption experiments allowed identification of subband energies and in-plane reduced masses. Using an 8ϫ8 k•p band-structure calculation which takes account of nonparabolicity, valence subband mixing, and strain effects, we are able to fit calculated absorption curves to transition energies and reduced masses. Comparison of fits on several samples confirm that the electrons lie in the In͑As,Sb͒ layer and the holes in the InAs layer. By using the fitted curve offsets, we are able to calculate the fractional conduction-band-offset parameter, Q c , which for a type-II heterostructure can be greater than 1 and which we found to be 2.

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300 K light-emitting diodes which emit at 5 and 8 μm with quasi-cw output powers of up to 50 and 24 μW, respectively, are reported. The devices have a single molecular beam epitaxy grown InAs/In(As, Sb) quantum well in the active region with a strong type-IIa band alignment giving mid-IR emission at energies up to 64% lower than the alloy band gap. The emission energies are shown to be in good agreement with a k⋅p bandstructure model where Qc, the ratio of the strained conduction-band offset to the band-gap difference between the two strained superlattice components, is found to be ∼2.0.

Articles you may be interested inThe electronic structure of InGaAs/InP quantum wells measured by Fourier transform photoluminescence excitation spectroscopy InAs/InAs 0.865 Sb 0.135 quantum wells are characterized using magneto-photoluminescence. Bandto-band transitions are found at energies lower than the band gaps of either the InAs or the InAs 0.865 Sb 0.135 with photoluminescence emission at wavelengths up to 4.8 m. By modeling the quantum size shifts of the photoluminescence transitions and their energy shift in a magnetic field, the valence band offset between InAs and In͑As,Sb͒ is deduced to be type II with electron confinement in the In͑As,Sb͒ alloy and hole confinement in InAs.