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There has been steady effort to advance Ga-free InAs1−xSbx/InAs1−ySby superlattice (SL) materials for long-wavelength infrared (LWIR) detector applications. Although Ga-free SLs grown pseudomorphically on GaSb wafers work well in mid-wavelength applications, most LWIR Ga-free SL designs suffer from relatively low optical absorption and poor hole transport. One of the main problems in using the Ga-free material system for LWIR applications is a tremendous constraint on band engineering imposed by matching the SL lattice parameter to the lattice constant of conventional GaSb substrates. In this work, we propose several lattice engineered short-period LWIR InAs1−xSbx/InAs1−ySby SL designs that can enhance optical absorption and vertical hole mobility at an 11 μm cutoff wavelength. We also performed test growths of the designed structures on lattice-matched homogeneous buffer layers on GaAs wafers. [ABSTRACT FROM AUTHOR]

Digital alloy Al0.85Ga0.15As0.56Sb0.44 and random alloy Al0.79In0.21As0.74Sb0.26 avalanche photodiodes with a 1-μm multiplication layer exhibit low excess noise under 543-nm laser illumination comparable to Si avalanche photodiodes. This has motivated a study of the optical characteristics of these materials. The absorption coefficients and complex refractive indices were extracted via variable-angle spectroscopic ellipsometry. Features of three semiconductor layer fitting approaches are compared, and a Kramers–Kronig-consistent basis spline function was chosen due to its flexibility and accuracy of approximating optical constants of quaternary materials. The external quantum efficiency has been calculated based on the extracted absorption coefficients and is shown to agree well with the measured external quantum efficiency. [ABSTRACT FROM AUTHOR]

The defect structures in HgTe/CdTe superlattices (SLs) on CdTe/Si(211)B substrates grown by molecular-beam epitaxy have been investigated using (scanning) transmission electron microscopy and electron energy loss spectroscopy. Straight Hg-rich defects perpendicular to the SLs have been observed near the substrate while Frank dislocation loops (FDLs) are seen far from the substrate. The Hg-rich defects exhibit only a compositional variation with no significant atomic shift, and can be considered to be a remnant of a FDL which has climbed by thermal diffusion during the growth. [ABSTRACT FROM AUTHOR]

HgTe/CdTe superlattices (SLs) have been grown on CdZnTe (211)B substrates as interfacial layers to improve the reproducibility and material properties of epitaxial HgCdTe. The interfacial SL layer is found by transmission electron microscopy to be capable of smoothing out the substrate’s surface roughness and to bend or block threading dislocations from propagating from the substrate into the functional HgCdTe epilayers. The best etch pit density values of 4×104 cm-2 were achieved in long-wavelength infrared HgCdTe epilayers with such interfacial layers, while typical values were in the low 105 cm-2 range. The recombination mechanisms in such layers were dominated by radiative and Auger intrinsic recombination mechanisms, whereas the contributions from the Shockley-Read-Hall mechanism become negligible, which demonstrated that the use of the SL interfacial layers was beneficial for HgCdTe growth using molecular beam epitaxy or MBE. [ABSTRACT FROM AUTHOR]

The effects of disorder on Auger recombination lifetimes in strained-layer type-II superlattices are estimated. Disorder is modeled in two ways: (i) by completely neglecting momentum conservation in Auger transitions, and (ii) by including phonon scattering in the transitions. The purpose of (i) is to obtain establish bounds on the effects of disorder, and of (ii) to provide more realistic lifetime estimates for high-quality materials. In both cases, the disorder is assumed to be less severe than what would cause significant changes in the electronic band structure. The complete relaxation of momentum conservation results in Auger lifetimes decreasing by approximately one order of magnitude. However, electron-phonon effects have a relatively small effect because the interaction is weak. Hence, the benefits of band engineering in such superlattices remain substantial even in the presence of typical disorder. [ABSTRACT FROM AUTHOR]

A comparison is performed between measured and calculated Auger recombination rates for four different narrow-gap superlattices based on the InAs/GaSb/AlSb material system. The structures are designed for optical or electrical injection for mid-infrared laser applications, with wavelengths ranging from 3.4 to 4.1 µm. The electronic band structures are computed employing an accurate 14-band restricted basis set (superlattice K·p) methodology that utilizes experimental information about the low-energy electronic structure of the bulk constituents. The superlattice band structures and their associated matrix elements are directly employed to compute Auger recombination rates. Varying amounts of Auger recombination suppression are displayed by the various superlattices as compared to bulk mid-infrared systems. The greatest disagreement between theory and experiment is shown for the structure predicted to have the most Auger suppression, suggesting the suppression is sensitive either to theoretical or growth uncertainties. [ABSTRACT FROM AUTHOR]

We study the effects of the electronic band structure on the hole- and electron-initiated impact ionization in Sb-based superlattice avalanche photodiodes. Earlier calculations have revealed that bulk alloy A1GaSb avalanche photodiodes with alloy composition near the resonance between the energy gap and the spin-orbit splitting have an enhanced hole to electron impact ionization coefficient ratio for a low electric field but not for a high electric field. The absence of an enhancement under high fields is due to carrier heating spreading the hole distribution in the splitoff band. A strategy to extend this type of enhancement to high fields in a superlattice involves band engineering the superlattice to place flat bands at approximately one energy gap below the top of the valence band. This prevents holes from spreading in energy and hence gives rise to strong hole-initiated impact ionization. Quantitative results are presented for short-infrared AlAs/InGaAs/ AlAs/InGaSb, midinfrared InAs/InGaSb/AlSb, and long-infrared InAs/InGaSb/AlSb superlattices. [ABSTRACT FROM AUTHOR]

Despite recent progress in electronic structure engineering of type-II materials for mid-infrared lasers, suppression of Auger recombination at room temperature has been limited. We present an active region design, consisting of AlAsSb/InAs/GaInSb/InAs/AlAsSb wells separated by an InAs/AlGaSb superlattice, that overcomes this limitation. The 300 K calculated Auger recombination rate in this structure at the optimal lasing density is five times smaller than typical Shockley-Read-Hall (defect-assisted) recombination rates. An integrated separate confinement heterostructure design suitable for this active region is also described. The separate confinement region, which is a lightly doped InAs/AlGaSb superlattice, provides efficient hole transport and injection into the active region. For an estimated nonactive region modal cavity loss of 20 cm-1 and an optical mode width of 1.3 μm, the calculated internal threshold current density is 100 A/cm2 at 300 K for a single quantum well device. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the performance characteristics of type-II InAs/In[subx]Ga[sub1-x]Sb superlattices for long and very long-wave infrared (IRA) detection. Information on the qualitative features of bands and Auger rates; Derivations of rates for band-to-band Auger recombination and shallow-trap Auger recombination in super lattices; Results for minority carrier lifetimes and IR photodiode detectivities of the superlattices.

Presents a study which calculated the ideal threshold current densities of IR lasers for active layers composed of indium arsenide/InGaSb superlattices, InGaAsSb quantum well quaternaries, InAsSb bulk ternaries, and HGCdTe superlattices. Formalism employed to calculate the superlattice band structure; Classes of laser structures considered in the study; Usefulness of band-structure engineering to obtain optimum laser performance.

Presents a reply to commentary on the article 'Temperature Limits on Infrared Detectivities of InAs/In[subx]Ga[sub1-x]Sb Superlattices and Bulk Hg[sub1-x]Cd[subx]Te,' which appeared in the 1993 issue of the 'Journal of Applied Physics.'

Focuses on a study which investigated the potential use of a superlattice system for midwave infrared injection laser applications. Information on the use of the superlattice in multispectral infrared applications; Conditions that promote short Auger lifetimes with increasing temperatures; Comparison of the radiative recombination and Auger lifetimes at threshold carrier densities.