A calculation on intersubband optical transitions including heavy and light hole bands to spin-split-off band in heavily doped p-type GaAs/AlGaAs multi-quantum well (MQW) structures is reported. The analysis is focused on elucidating the recent experimental observation of normal incidence absorption and photocurrent at photon wavelengths of 2–3 μm, in addition to the already-observed absorption at around 8 μm in heavily doped p-type GaAs/AlGaAs MQW structures. The calculation is an extension of our previous study which only includes transitions between heavy and light bands. The analysis, in which Hartree and exchange-correlation many-body interactions are taken into account within one-particle local density approximation, shows that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than the barrier height for p-type GaAs/AlGaAs superlattices with well doping of 2×1019 cm−3. One region has broad absorption peaks with coefficients of about 5000 cm−1 at around 8 μm, and the other has two rather sharp peaks at 2.7 and 3.4 μm with 1800 and 1300 cm−1, respectively. The result agrees reasonable well with the experimental observation in general absorption features. The existence of multiabsorption wavelengths in heavily doped GaAs/AlGaAs MQWs may allow the design of multicolor normal incidence photodetectors.
Epitaxial layers of GaAs with peak mobilities as high as 200 000 cm2/V s at 50 K have been grown in an atmospheric pressure organometallic vapor phase epitaxy reactor using trimethylgallium (TMG) and arsine. The growth conditions which lead to high-mobility GaAs are described in this letter. Low-temperature photoluminescence and temperature-dependent Hall measurements are used to study the dependence of the incorporation of residual impurities on the growth temperature and arsine partial pressure. Carbon acceptor densities <1014 cm−3 were measured in the highest purity samples.
Residential non-hardware 'soft costs' can be substantially reduced by simplifying photovoltaic (PV) installation. Adhesive mounting of lightweight (glassless, frameless) PV modules onto steep-slope shingled roofs eliminates roof penetration and the need for structural review. In this work, adhesive performance is evaluated via pull-testing, creep testing as well as durability testing. Results show adhesive uplift resistance sufficient for 150mph wind (safety factor = 2) and an increase in adhesion after most aging tests. Creep is observed at extreme roof-pitch and high temperature. An approach to predicting creep over the lifetime of a PV installation is outlined
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