Evaluation of data obtained from deep level transient spectroscopy (DLTS) is often based on the assumption that the transients are exponential. The applicability of DLTS to the study of deep energy levels in semiconductor alloys has therefore been questioned since thermal transients are often nonexponential in these materials. In this paper we present calculated DLTS spectra in a simple model for broadened defect levels. The calculated spectra are compared with experimental data for a deep electron trap in GaAs1−xPx . The main result is that, within the model, DLTS-deduced activation energies and thermal emission rates are, indeed, relevant even when the transients are strongly nonexponential as a result of alloy broadening. A method of estimating the corrected concentration of deep levels and the distribution in binding energies is also presented.
The chalcogens S, Se, and Te have been introduced by diffusion into single-crystal germanium. .Both thermaland optical-junction space-charge techniques have been performed in parallel with photoconductivity studies using a Fourier-transform spectrometer. Electronic levels within the energy gap have been monitored from both valence and conduction bands using various techniques.The suggested double-donor states are found to be at Ec -0.28 and Ec -0.59 eV for sulfur, Ec -0.268 and E& -0.512 eV for selenium, and E& -0.093 and Ec -0.33 eV for tellurium. Evidence is found for excited states of S, Se, and Te. The neutral center of Se exhibits line spectra and corresponding Fano resonances due to a I 0 intravalley phonon. The binding energy of the neutral 2s ( A &) state of 7.4 meV is reported. A fitting of the spectra of deeper Se levels is in agreement with a singly ionized center. Electron thermal-emission rates and capture cross sections are reported for the Ec -0.268, Ec -0.28, and E& -0.33 levels. The capture cross section of the latter shows a T " temperature dependence. Furthermore, an unidentified double donor exhibiting excited states is found in several samples, having a binding energy of 207 meV. It is suggested to be oxygen related. Finally a comparison is made with data obtained from chalcogen-doped silicon.
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