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A detailed characterization of the impurity centers involved in the photoluminescence (PL) of p‐type CdTe doped with arsenic (As) and antimony (Sb) has been performed. The PL spectrum has been measured from 1.35 eV up to the band edge and as a function of temperature (4.2 up to 30 K). In addition to the familiar broad PL line centered at 1.45 eV and present in undoped and doped materials, the doped samples exhibit a new band near 1.54 eV showing a fine structure composed of two peaks whose intensities vary with temperature. The observed longitudinal optical (LO) phonon replicas associated with the zero‐phonon lines, at 1.45 eV and 1.54 eV, respectively, are characterized by a Huang‐Rhys factor S=1.3±0.1 and S=0.30±0.02. The various electron‐hole recombination processes are explained by means of a simple analytic model correlating the position of the zero‐phonon lines to the relative intensities of the phonon side bands. The model accounts for the chemical shift of the defect centers and describes the effe...

In this paper we study the low‐lying energy levels of Co2+ and Fe2+ in diluted magnetic semiconductors, such as Cd1−xCoxTe and Cd1−xCoxSe, and their iron‐based counterparts. In the first of these compounds, the magnetic ion sits on a site of symmetry Td, while in the second the symmetry is trigonal (C3v). We develop a formulation that permits a continuous variation from Td to C3v symmetry. Comparison with experimental data in Cd1−xCoxSe shows that the C3v distortion amounts to about 10% of the crystal potential at the Co2+ site. Our study of the energy spectra of Fe2+ in Td and C3v crystal potentials reveals that, even in the cubic field, the levels exhibit an anisotropy which manifests itself in an anisotropy of the magnetization M in the regime in which M is not a linear function of the magnetic field B. The study includes all the levels in the lowest terms of the (3d)7 and (3d)6 configurations of Co2+ and Fe2+, thus considerably extending work by previous authors. The calculations are carried out to se...

A coherent analysis of the near-band-edge luminescence spectra of undoped and Si-doped GaN layers grown by metalorganic vapor phase epitaxy on a sapphire substrate has been performed with a model including the effect of the charge carrier–longitudinal optical (LO) phonon interaction, based on Frohlich’s polaron theory. This model allows one to correlate the relative intensities of the phonon sidebands to the position of the zero-phonon line from which ionization energies are obtained. Moreover, central-cell corrections are taken into account using two different models: the quantum defect model and the Lucovsky model [Solid State Comm. 3, 299 (1965)]. The effect of the electron-LO phonon interaction has been included in these models. Comparison between theory and experiment through the Huang-Rhys factor [Proc. Roy Soc. A204, 406 (1950)] allows a precise determination of the impurity binding energies and effective radii, as well as a reliable characterization of the charge carrier–LO phonon interaction.

A study is given of the effect of ultrasonic generation on the residual surface impedance of superconductors at microwave frequencies. We present an exact solution of the problem for London superconductors and give also general expressions for the residual surface resistance at zero temperature. Universal curves of the residual resistance as a function of the frequency and of the ratio of the correlation length to the electron mean free path are given using the Pippard and BCS kernels. Our investigation yields a lower limit to the surface impedance within the limits of the use of the free‐electon model. A comparison is given with experimental data available in the literature for niobium, lead, and indium as well as a critical analysis of previous theoretical work. For indium and lead our results are one or two orders of magnitude below selected experimental results. For niobium, the lowest experimental results agree fairly well with those estimated in the present work.

A theoretical study of the effect of direct ultrasonic generation on the surface impedance of superconductors at temperatures below the critical temperature Tc is presented. The temperature and frequency dependences of the additional surface resistance due to the ionic motion are analyzed using the Pippard and BCS kernels and parabolic electron energy bands.

An analytical model for the oscillatory behavior of the photoconductivity excitation spectrum in the photoconductivity of polar semiconductors is presented. The model is a simple version of the theory by Stocker and Kaplan [Phys. Rev. 150, 619 (1966)], modified to include the effects of thermal longitudinal optical phonons. The theory is applied to the case of n‐type CdTe. Comparison with the experimental results of Nicholas et al. [J. Phys. C 13, 5215 (1980)] suggests the existence of three trapping mechanisms: phonon‐assisted trapping by donor levels lying, respectively, at Ee=3 meV and E0=12 meV below the conduction band edge, and a direct capture by very shallow states acting on the slow electrons at the bottom of the band. A value of τ=2.2×10−12 s is obtained for the average lifetime of the electrons in the conduction band.