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The optical properties of GaAs"Sbl "alloys grown across the entire concentration range by multitarget sputter deposition are reported. X-ray diffraction, optical absorption, and Raman spectra show the samples to be single-crystal, single-phase alloys for all x, including those in the miscibility gap. Alloy lattice constants are found to vary linearly with concentration. The direct I -point energy gaps, determined from optical-absorption measurements, show significant negative bowing.Contrary to previous reports, the Raman spectra exhibit two-mode behavior throughout, including a local mode of As in GaSb and a resonant mode of Sb in GaAs. An analysis of peak frequencies and line shapes versus concentration is given in the context of disorder effects. %e observe broadenings much less severe and asymmetric than those seen in similar systems and usually interpreted in terms of k&0 density-of-states activation. The observed adherence to zone-center selection rules for all x, suggests a more accurate interpretation to be one involving the k =0 spectral projection of the density of states.

Photodiodes with epitaxial CoSi2 particles embedded in a single-crystal silicon matrix show response in the 1–2 μm range with structure which correlates with absorption peaks due to the surface plasmon resonance of the particles. Aspect ratios (height:diameter) of the particles are accurately controlled by molecular beam epitaxy over a range from 1.4:1 to 1:7, allowing the absorption peaks to be tailored from 1.2 to 2.6 μm, respectively. The particle surface plasmon excitation modifies the photoresponse of the devices and allows this response to be tailored through control of the dimensions of the particles. The photodiodes were tested at 77 K, and 4 of 8 devices tested with an absorption peak at 1.7 μm show dark currents less than 2 nA/cm2 at a reverse bias of 1 V. Detectivities for the same devices at 77 K range from 4×109 to 8×109 cm√Hz/W.

We have fabricated and characterized six-element monolithic arrays of Ge:Ga blocked- impurity-band detectors, with threshold wavelength 220 μm, peak quantum efficiency 14%, detective quantum efficiency 9%, dark current 300 e− s−1, and response uniformity better than 4%. The devices are described very well by the standard model of blocked-impurity-band detectors, and appear to satisfy many of the requirements of low-background astronomical instruments.