S.G. Bishop

Optical and ESR analysis of the Fe acceptor in InP

Abstract Photoluminescence (PL), optical absorption, and electron spin resonance (ESR) have been applied to detect the different charge states of substitutional Fe in InP. The 3 d 6 one electron trap state is detected by the PL and optical absorption lines of the 5 T 2 − 5 E transitions, whereas the 3 d 5 neutral acceptor state is identified by its characteristics S = 5/2 ESR signal.

Thermal degradation of homoepitaxial GaAs interfaces

Photoluminescence techniques have been used to detect and characterize p‐type conducting layers formed on the surface of semi‐insulating GaAs substrates and at the liquid phase epitaxial layer–GaAs substrate interface during pregrowth heat treatment. These layers contain ∼1017 cm−3 shallow acceptors and a high density of arsenic vacancy complexes, and can be eliminated by pregrowth Ga etching of the substrate.

Photoluminescence from deep centers in GaAs

Abstract Sharp line structure attributable to phonon assisted radiative emission has been observed in the 6 K photoluminescence spectra from deep centers in bulk samples of chromium doped GaAs. Two luminescence bands at 0.56 and 0.8 eV have been observed and both bands exhibit evidence of phonon assisted radiative recombination. An exploration of these luminescence bands in terms of excited state to ground state transitions of Cr3+ and Cr2+ ions is proposed.

Thermally generated paramagnetism in amorphous arsenic

Abstract A density of paramagnetic states which increases with temperature has been observed and characterized in amorphous As using ESR and optical absorption techniques. Unlike the chalcogenide amorphous semiconductors, these localized paramagnetic gap states are characterized by small effective electronic correlation energies (U) and are interpreted as resulting from thermal excitation of strained bonds at As vacancies.

Optically induced localized paramagnetic states in amorphous As

Abstract Photoluminescence and optically induced ESR and absorption due to localized states in the forbidden gap have been observed in amorphous As below 77 K. Analysis of the ESR spectru, indicates that these centers are highly localized and in orbitals which are predominantly p-like.

Iron impurities as non-radiative recombination centres in chalcogenide glasses

Abstract Photoluminescence and E.S.R. studies have been carried out on pure and iron-doped As2S3 glass. The luminescence spectra, photoluminescence excitation spectra, temperature dependence of the luminescence efficiency, and luminescence fatiguing curves demonstrate that the iron impurities quench the luminescence efficiency by introducing competing non-radiative recombination centres. The E.S.R. measurements reveal that iron is a pervasive inadvertent impurity even in nominally pure chalcogenide glasses. It is suggested that non-radiative recombination occurs by transfer of an excitons recombination energy to localized d-band excited states of an iron ion; the excited iron ion then relaxes non-radiatively by phonon emission.

Donor binding energies determined from temperature dependence of photoluminescence spectra in undoped and aluminum-doped beta SiC films

Measurements of the temperature dependence of N‐Al donor‐acceptor pair photoluminescence spectra in cubic SiC films demonstrate that the thermal activation energy for the nitrogen donors is equivalent to the 54 meV binding energy for nitrogen determined from the spectral energies of the sharp‐line close pair spectra. It follows that the 15–20 meV donor which dominates the electrical properties of n‐type films is not isolated, substitutional nitrogen. Spatial variations observed in the intensity of a new 2.368 eV luminescence band demonstrate that the radiative recombination centers are inhomogeneously distributed in the films.

Small angle X-ray scattering evidence for the absence of voids in chalcogenide glasses

Abstract Small angle X-ray scattering measurements show no evidence for the presence of voids in chalcogenide glasses, in contrast to the situation found in deposited films of Ge and Si. This result and the observation of a diffraction peak near k = 1.2 A −1 are found to be consistent with the existence of a layer structure in glassy As2S3 and As2Se3.

The effects of impurities upon photoluminescence and optically induced paramagnetic states in chalcogenide glasses

Abstract Photoluminescence (PL) and optically induced electron spin resonance (ESR) have been studied in As2Se3 glasses doped with Cu, Tl, I, Ag, In, and K and in B-doped As2S3 glass. In all cases there is no significant change in PL efficiency or intensity of induced ESR until dopant concentrations exceed ∼1 at.%. These results are in marked contrast the strong dependence of transient hole transport upon dopant concentration in the same glasses. These parallel but contrasting observations are discussed in terms of the predicted effects of dopants on defects in chalcogenide glasses postulated by Mott on the basis of the charged defect model of Mott, Davis and Street (MDS). PL and ESR studies of the AsSe glass system have revealed that oxygen contamination can severely quench PL efficiency and ESR intensity for As concentrations

Atomic reorientation rates in liquid chalcogenide glasses: NMR in Se and As2Se3

Temperature dependence of the NMR spectrum in liquid Se indicates that atomic reorientation in this molten ring-chain structure glass is governed by a distribution of correlation times with a median of τ∗ = 5 × 10−5sec at 220°C. In liquid layer structure glasses at equivalent viscosity, atomic reorientation rates are not sufficient to narrow observed NMR spectra. SeSe and AsSe bonds in glassy Se and As2Se3 are distinguishable on the basis of their chemically shifted Se77 NMR spectra.