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An approach to derive the below-bandgap absorption in GaSb/GaAs self-assembled quantum dot devices using room-temperature external quantum efficiency measurement results is presented. Devices with five layers of delta-doped quantum dots placed in the intrinsic, n- and p-regions of a GaAs solar cell are studied. The importance of incorporating an extended Urbach tail absorption in analyzing the absorption strength of quantum dots and the transition states is demonstrated. The theoretically integrated absorbance via quantum dot ground states is calculated as 1.04 × 1015 cm−1s−1, which is in reasonable agreement with the experimentally derived value 8.1 × 1015 cm−1s−1. The wetting layer and quantum dot absorption contributions are separated from the tail absorption and their transition energies are calculated. Using these transition energies and the GaAs energy gap of 1.42 eV, the heavy hole confinement energies for the quantum dots (320 meV) and for the wetting layer (120 meV) are estimated.

Abstract ULTRARAM is a nonvolatile memory with the potential to achieve fast, ultralow‐energy electron storage in a floating gate accessed through a triple‐barrier resonant tunneling heterostructure. Here its implementation is reported on a Si substrate; a vital step toward cost‐effective mass production. Sample growth using molecular beam epitaxy commences with deposition of an AlSb nucleation layer to seed the growth of a GaSb buffer layer, followed by the III–V memory epilayers. Fabricated single‐cell memories show clear 0/1 logic‐state contrast after ≤10 ms duration program/erase pulses of ≈2.5 V, a remarkably fast switching speed for 10 and 20 µm devices. Furthermore, the combination of low voltage and small device capacitance per unit area results in a switching energy that is orders of magnitude lower than dynamic random access memory and flash, for a given cell size. Extended testing of devices reveals retention in excess of 1000 years and degradation‐free endurance of over 107 program/erase cycles, surpassing very recent results for similar devices on GaAs substrates.

Silicon photonics has emerged as the most promising technology for next-generation compact optoelectronic systems, but further development is still required to achieve efficient and reliable on-chip light sources. Direct epitaxial growth of antimonide-based compound semiconductor materials on silicon provides a pathway toward the monolithic integration of new, mid-infrared solid-state light sources and comprehensive photonic circuits on silicon platforms. Such devices have wide-ranging applications in environmental monitoring and medical diagnostics. This paper reports on the realization of a mid-infrared InAsSb light emitting diode directly integrated onto silicon using molecular beam epitaxy. The heteroepitaxial integration of the InAsSb p-i-n device onto silicon was achieved with the use of a novel, antiphase domain-free, GaSb-on-silicon buffer layer. The device exhibited efficient light emission at room temperature, peaking at around 4.5 μm, which corresponds well to the CO2 atmospheric absorption band. An output power of 6 μW and an external quantum efficiency of 0.011% was measured at 300 K. These results demonstrate mid-infrared III-V light emitting diodes can be directly grown on silicon, which is an essential step towards the realization of the next generation, on-chip integrated light sources.

We analyse the optical properties of InAs1−xSbx/Aly In1−y As quantum wells (QWs) grown by molecular beam epitaxy on relaxed Aly In1−y As metamorphic buffer layers (MBLs) using GaAs substrates. The use of Aly In1−y As MBLs allows for the growth of QWs having large type-I band offsets, and emission wavelengths  >3 m. Photoluminescence (PL) measurements for QWs having Sb compositions up to x  =  10% demonstrate strong room temperature PL up to 3.4 m, as well as enhancement of the PL intensity with increasing wavelength. To quantify the trends in the measured PL we calculate the QW spontaneous emission (SE), using a theoretical model based on an eight-band Hamiltonian. The theoretical calculations, which are in good agreement with experiment, identify that the observed enhancement in PL intensity with increasing wavelength is associated with the impact of compressive strain on the QW valence band structure, which reduces the band edge density of states making more carriers available to undergo radiative recombination at fixed carrier density. Our results highlight the potential of type-I InAs1−xSbx/Aly In1−y As metamorphic QWs to address several limitations associated with existing heterostructures operating in the mid-infrared, establishing these novel heterostructures as a suitable platform for the development of light-emitting diodes and diode lasers. [ABSTRACT FROM AUTHOR]

This article demonstrates the innovative use of the log-linear distance model in the assessment of homophily in a set of small groups, such as the co-participants in a set of events. It traces the development of the application of the log-linear distance model to the study of homophily and reviews its recent use to assess the extent and structure of gender and age homophily in groups of criminal accomplices (‘co-offenders’). The transformations of the group membership data that are a prerequisite of the log-linear analysis, and the interpretation of the log-linear parameters, are explained in detail in order to make the approach accessible to potential users. Although the described applications are to gender and age homophily in groups of criminal accomplices, the method can be used to assess homophily on one or more variables in any small groups.