Heterostructures and infrared emitters with compressed InAsSb layers

An overview is presented of strained InAsSb heterostructures and infrared emitters. InAsSb/InGaAs strained-layer superlattices (SLS) and InAsSb quantum wells were characterized using magneto-photoluminescence and compared with unstrained InAsSb and InAs alloys. In heterostructures with biaxially compressed InAsSb, large quantum confinement energies were observed, and the holes exhibited a decrease in effective mass, approaching that of the electrons. This study demonstrates that the electrons and holes in the InAsSb heterostructures are confined in the InAsSb layers, and the band offsets are type I. A large increase in the Auger-1 threshold energy should accompany the strain-induced change in valence-band symmetry of the InAsSb layers. Correspondingly, the InAsSb heterostructures display high radiative efficiencies and increased activation energies for nonradiative recombination compared with the unstrained alloys. LEDs and L-mrs with InAsSb heterostructure active regions are described. InAsSb/InGaAs SLS LEDs operating at 300K at wavelengths {le} 5 pm have been demonstrated. Optically pumped InAsSb/InGaAs SLS lasers, with InPSb cladding, had a maximum operating temperature of 100K

Auger rates in mid-IR InAsSb laser structures

Auger rates are calculated for three InAsSb mid-infrared laser structures as a function of temperature. Compressive strain in the quantum wells reduces the mass of the holes; it is shown that this leads to a reduction in the Auger rate compared with an unstrained quantum well. The Auger rates for these structures are similar primarily due to their similar bandgap energies

Exploration of GaInT1P and Related T1-Containing III-V Alloys for Photovoltaics

This paper discusses the results of an attempt to grow GaInTlP for application as a 1-eV material for the third junction of a GaInP/GaAs/3rd-junction high-efficiency solar cell. Although early indications from the literature were promising, we are unable to produce crystalline homogeneous material, and so we conclude that this material is not a promising candidate for such applications as photovoltaics

Interfaces in InAsSb/InGaAs strained-layer superlattices grown by MOCVD for use in infrared emitters

The authors have prepared InAsSb/InGaAs strained-layer superlattices (SLSs) using metal-organic chemical vapor deposition (MOCVD). X-ray diffraction was used to determine lattice matching as well as composition and structure of the SLS`s. The presence of an InGaAsSb interface layer was indicated by x-ray diffraction for samples grown under non-optimized conditions. Interfacial layers were also identified with transmission electron microscopy (TEM). Two types of interfaces were observed by TEM. The different contrasts observed by TEM could be due to a difference in composition at the interfaces. The width of the x-ray peaks can be explained by a variation of the layer thickness

Use of high index substrates to enable dislocation filtering in large mismatch systems

We report results in three areas of research relevant to the fabrication of a wide range of optoelectronic devices: The development of a new x-ray diffraction technique that can be used to rapidly determine the optimal period of a strained layer superlattice to maximize the dislocation filtering; The optimal MBE growth parameters for the growth of CdTe on GaAs(211); The determination of the relative efficiency of dislocation filtering in the (211) and (100) orientations; and The surface quality of InSb grown by MOCVD on InSb substrates is affected by the misorientation of the substrate

Development of InAsSb-based light-emitting diodes for chemical sensing systems

Mid-infrared (3--6 {micro}m) LED`s are being developed for use in chemical sensor systems. As rich, InAsSb heterostructures are particularly suited for optical emitters in the mid-infrared region. The authors are investigating both InAsSb-InAs multiple quantum well (MQW) and InAsSb-InAsP strained layer superlattice (SLS) structures for use as the active region for light emitting diodes (LED`s). The addition of phosphorus to the InAs barriers increases the light and heavy hole splitting and hence reduces non-radiative Auger recombination and provides for better electron and hole confinement in the InAsSb quantum well. Low temperature (< 20 K) photoluminescence (PL) emission from MQW structures is observed between 3.2 to 6.0 {micro}m for InAsSb wells between 70 to 100 {angstrom} and antimony mole fractions between 0.04 to 0.18. Room temperature PL has been observed to 6.4 {micro}m in MQW structures. The additional confinement by InAsP barriers results in low temperature PL being observed over a narrower range (3.2 to 5.0 {micro}m) for the similar well thicknesses with antimony mole fractions between 0.10 to 0.24. Room temperature photoluminescence was observed to 5.8 {micro}m in SLS structures. The addition of a p-AlAsSb layer between the n-type active region (MQW or SLS) and a p-GaAsSb contact layer improves electron confinement of the active region and increases output power by a factor of 4. Simple LED emitters have been fabricated which exhibit an average power at room temperature of > 100 {micro}W at 4.0 {micro}m for SLS active regions. These LED`s have been used to detect CO{sub 2} concentrations down to 24 ppm in a first generation, non-cryogenic sensor system. They will report on the development of novel LED device designs that are expected to lead to further improvements in output power

Medium properties and total energy coupling in underground explosions

A phenomenological model is presented that allows the direct calculation of the effects of variations in medium properties on the total energy coupling between the medium and an underground explosion. The model presented is based upon the assumption that the shock wave generated in the medium can be described as a spherical blast wave at early times. The total energy coupled to the medium is then simply the sum of the kinetic and internal energies of this blast wave. Results obtained by use of this model indicate that the energy coupling is more strongly affected by the medium's porosity than by its water content. These results agree well with those obtained by summing the energy deposited by the blast wave as a function of range. (auth