R. H. Miles

Auger lifetime enhancement in InAs–Ga1−xInxSb superlattices

We have experimentally and theoretically investigated the Auger recombination lifetime in InAs–Ga1−xInxSb superlattices. Data were obtained by analyzing the steady‐state photoconductive response to frequency‐doubled CO2 radiation, at intensities varying by over four orders of magnitude. Theoretical Auger rates were derived, based on a k⋅p calculation of the superlattice band structure in a model which employs no adjustable parameters. At 77 K, both experiment and theory yield Auger lifetimes which are approximately two orders of magnitude longer than those in Hg1−xCdxTe with the same energy gap. This finding has highly favorable implications for the application of InAs–Ga1−xInxSb superlattices to infrared detector and nonlinear optical devices.

Auger coefficients in type-II InAs/Ga1−xInxSb quantum wells

Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 μm, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure.

Mid-wave infrared diode lasers based on GaInSb/InAs and InAs/AlSb superlattices

We report the characterization of a set of broad‐area semiconductor diode lasers with mid‐wave infrared (3–5 μm) emission wavelengths. The active region of each laser structure is a 5‐ or 6‐period multiple quantum well (MQW) with Ga0.75In0.25As0.22Sb0.78 barriers and type‐II (broken‐gap) Ga0.75In0.25Sb/InAs superlattice wells. The cladding layers of each laser structure are n‐ and p‐type InAs/AlSb (24 A /24 A) superlattices grown lattice‐matched to a GaSb substrate. By tailoring constituent layer thicknesses in the Ga0.75In0.25Sb/InAs superlattice wells, laser emission wavelengths ranging from 3.28 μm (maximum operating temperature=170 K) to 3.90 μm (maximum operating temperature=84 K) are obtained.

Midwave infrared stimulated emission from a GaInSb/InAs superlattice

Use of a cracked Sb source and a postgrowth anneal procedure has been found to yield significant improvements in optical efficiencies of GaInSb/InAs superlattices grown by molecular beam epitaxy. Appreciable 5 μm band‐to‐band luminescence has been observed at room temperature, and stimulated emission at 3.2 μm has been demonstrated in an optically pumped structure. Intrinsic properties of this class of superlattices favor them for application as efficient infrared lasers operating at comparatively high temperatures.

Infrared optical characterization of InAs/Ga1−xInxSb superlattices

InAs/Ga1−xInxSb superlattices have been examined by photoluminescence, photoconductivity, and infrared optical transmission. Samples display clear photoconductive thresholds at energies in agreement with band gaps derived from photoluminescence. Far‐infrared energy gaps (8–14 μm and beyond) are obtained for InAs/Ga0.75In0.25Sb superlattices with periods <75 A, in good agreement with gaps calculated from a simple two‐band model. An absorption coefficient of ∼2000 cm−1 at 10 μm is measured in a superlattice with an energy gap of 11.4 μm. The magnitude and shape of this absorption edge is comparable to that of bulk Hg1−xCdxTe, suggesting that infrared detectors based on InAs/Ga1−xInxSb superlattices may be competitive in the 8–14 μm range and beyond.

Theoretical performance limits of 2.1–4.1 μm InAs/InGaSb, HgCdTe, and InGaAsSb lasers

Ideal threshold current densities of 2.1–4.1 μm IR lasers are calculated for active layers composed of InAs/InGaSb superlattices, InGaAsSb quantum well quaternaries, InAsSb bulk ternaries, and HgCdTe superlattices. The fully K‐dependent band structure and momentum matrix elements, obtained from a superlattice K⋅p calculation, are used to calculate the limiting Auger and radiative recombination rates and the threshold current density. InGaAsSb quantum wells and InAs/InGaSb superlattices are found to be more promising laser candidates than HgCdTe superlattices and InAsSb bulk ternaries. The calculated threshold current densities of InAs/InGaSb superlattices are similar to those of InGaAsSb active layers at 2.1 μm, but are significantly lower at longer wavelengths. Comparison with experiment indicates that the threshold current densities of InGaAsSb‐based devices are about three times greater than those calculated for 25 cm−1 gain. The threshold current densities of present InAs/InGaSb superlattices are abou...

Growth and characterization of InAs/Ga1−xInxSb strained‐layer superlattices

We report the successful growth of InAs/Ga1−xInxSb strained‐layer superlattices, which have been proposed for far‐infrared applications. The samples were grown by molecular beam epitaxy, and characterized by reflection high‐energy electron diffraction, x‐ray diffraction, and photoluminescence. Best structural quality is achieved for superlattices grown on thick, strain‐relaxed, GaSb buffer layers on GaAs substrates at fairly low substrate temperatures (<400 °C). Photoluminescence measurements indicate that the energy gaps of the strained‐layer superlattices are smaller than those of InAs/GaSb superlattices with the same layer thicknesses, in agreement with the theoretical predictions of Smith and Mailhiot [J. Appl. Phys. 62, 2545 (1987)]. In the case of a 37 A/25 A, InAs/Ga0.75In0.25Sb superlattice, an energy gap of 140±40 meV (≊9 μm) is measured. This result demonstrates that far‐infrared cutoff wavelengths are compatible with short superlattice periods in this material system.

Atomic antimony for molecular beam epitaxy of high quality III–V semiconductor alloys

The product distribution of an antimony cracking effusion cell has been characterized using a time‐of‐flight mass spectrometer employing resonance‐enhanced laser ionization. Source operating conditions have been identified under which predominately tetramers, dimers, and monomers of antimony are produced. Molecular beam epitaxy experiments employing the characterized antimony source for the growth of antimonide/arsenide superlattices and GaSb epilayers show that significant improvements in material quality can be obtained using monomeric antimony over that using molecular antimony species. A comparison of the surface chemistry of atomic and diatomic antimony species in the growth of several Sb‐containing semiconductors will be presented.

Interface roughness scattering in semiconducting and semimetallic InAs‐Ga1−xInxSb superlattices

An analysis of magnetotransport results for InAs‐Ga1−xInxSb superlattices with a range of layer thicknesses demonstrates that interface roughness scattering dominates the electron mobility under most conditions of interest for infrared detector applications. However, the dependence on well thickness is much weaker than the d16 relation observed in other systems with thicker barriers, which is consistent with predictions based on the sensitivity of the energy levels to roughness fluctuations. Theory also correctly predicts an abrupt mobility decrease at the semiconductor‐to‐semimetal transition point, as well as the coexistence of two electron species in semimetallic samples.

Anisotropy and growth-sequence dependence of atomic-scale interface structure in InAs/Ga1−xInxSb superlattices

We have used cross-sectional scanning tunneling microscopy to study the atomic-scale interface structure of InAs/Ga1−xInxSb superlattices grown by molecular beam epitaxy. Detailed, quantitative analysis of interface profiles obtained from constant-current images of both (110) and (110) cross-sectional planes of the superlattice indicate that interfaces in the (110) plane exhibit a higher degree of interface roughness than those in the (110) plane, and that the Ga1−xInxSb-on-InAs interfaces are rougher than the InAs-on-Ga1−xInxSb interfaces. The roughness data are consistent with anisotropy in interface structure arising from anisotropic island formation during growth, and in addition a growth-sequence-dependent interface asymmetry resulting from differences in interfacial bond structure between the superlattice layers.