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We present a detailed procedure for calculating confined energy levels of strained-layer Ge,Si, -,/Si valence-band quantum wells as a function of Ge concentration x and well width L. The method assumes noncoupled wells and takes into account strain and spin-orbit-induced band shifts and splitting. We illustrate the method and find the heavy-hole (hh), light-hole (lh), and spin-orbit split-off (so) subband energy levels for wells deposited on Si(OO1) and Si(ll1) oriented substrates. We show results for L =40 A and Ge concentrations between x=0.0 and x=0.8, and for composition x =0.25 and well widths between L =O.O and L = 100 A. We plot (x,L) sets which give transition wavelengths between 10 and 11 ,um, the central region of an atmospheric transmission window of interest to infrared detector applications. We find that hh ground to excited-state transitions are more sensitive to well width variations, whereas hh to lh or hh to so transitions are more composition dependent. There are (x,L) combinations which permit both hh ground to excited state and hh to lh transitions. Such regions may possess strong absorption cross sections both for excitation at normal incidence and for illumination at an angle. Energy levels for the two substrate orientations are qualitatively similar, but for Si(ll1) the corresponding transitions occur at smaller x and L. The smaller L minimizes strain relaxation effects.[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 130.88.90.140 On: Wed, 03 Dec 2014 17:32:24

As-received and 60Co-irradiated cultured quartz is characterized using low-temperature near-infrared Fourier spectroscopy, and peaks associated with as-grown hydroxide (OH) and aluminum hydroxide (Al-OH) point-defect centers are measured. Defect-center distributions are determined from scanning small crystal regions parallel or normal to the crystal-growth axis. Large variations in point defects are observed arising from variations in substitutional and interstitial impurity concentrations along the crystal-growth axis. For the initial radiation doses as-grown OH decreases uniformly across the crystal and forms Al-OH, but Al-OH peak strength varies considerably in different crystal sections. This indicates the possibility of radiation-induced hydrogen diffusion over large distances to compensate nonuniformities in aluminum-ion distribution. With increasing dose as-grown OH may stabilize to a constant level in some crystal regions but deplete in other sections. For some crystals, Al-OH continues to form even after all as-grown OH is depleted, indicating an additional internal hydrogen-ion source. Sweeping (electrodiffusing) an irradiated sample in an air atmosphere restores as-grown OH, retains the radiation-induced Al-OH, and in samples with high as-grown OH concentrations creates a series of small bands in the frequency range of 3450 to 3625 cm−1.

throughout the crystal, and so long as the electron diGusion length is more than a few atomic spacings, any charge-compensating center will be produced too far from the V'+ to acct it appreciably. This conclusion is con6rmed by the experimental fact that no deviation from trigonal synonetry, such as would be produced Infrared transmission and reQection measurements have been made on nand p-type semiconducting Mg&Sn single crystals of different impurity concentrations between 2 and 30 tabb, at temperatures ranging from 15 to 296'K. At incident energies less than 0.22 eV, strong free-carrier absorption is present; with a as the absorption coeKcient and X, the wavelength, this may be expressed as 0. =cX't' at all temperatures where acoustical mode lattice scattering predominates. The absorption spectra due to other mechanisms has been analyzed after subtraction of the )'t" free-carrier dependence. At energies of 0.22 eV and above, the rapid increase in absorption is attributed to the intrinsic edge. From the energy dependence of the absorption coefBcient in the edge region, the mechanism of indirect transitions between the valence and conduction band can be established, with a phonon energy of 0.008 eV. A band in the 0.08 to 0.22 eV energy range present at all temperatures in n-type and above 196'K in p-type samples is interpreted in terms of transitions between two conduction band minima separated by 0.165 eV at 15'K. Below 0.06 eV an additional sharp rise in absorption occurs. A peak in this absorption at 26 p may correspond to a second harmonic of the fundamental lattice vibration which is centered around 53 p, . An energy band picture for Mg&Sn is suggested, and conductivity (m"*=0. 15m, m&*=0.10m), and density of states (m"*=1. 2m, m2, *=1. 3m) effective masses are calculated.