Theoretical and practical research of the use of inductors for improving DLTS characterization of semiconductors

In 1982 Broniatowki [J. Appl. Phys. 56 (1982) 2907] estimated theoretically what is the change of capacitance as seen by a capacitance meter if an inductor is set in series with a DLTS sample. To the best of our knowledge, there have been no experimental studies on the inductor coupled in series with the sample to clarify in which way the inductor would actually change the DLTS spectra. In this paper, we study for the first time theoretically and experimentally, the effects of an inductor on the capacitance of a sample, as seen by the capacitance meter. We also determine the resonance condition that increases the measured signal and we also study the separation of the signal peaks, proposing a novel way to obtain the activation energy ðEaÞ; the capture cross-section ðsÞ; and the density ðNÞ of deep levels. Finally, we show our preliminary results using light in connection with the inductor in DLTS to improve the accuracy of the measurements. As an illustrative example, we have investigated the DLTS of AlxGa1 2 xAs, with Al molar compositions of x 1⁄4 0:22; 0.3, 0.4, 0.6 and 0.92. Both doped and un-doped samples are studied. AlGaAs is known to exhibit at least four DX centres [J. Appl. Phys. 67 (1990) R1; Semicond. Semimetals 38 (1993) 235; International Symposium, Mauterndorf, Austria, 1991; J. Electron. Mater. 20 (1991) 1], the properties of which depend on x; but they are found to overlap with each other, which makes it hard to determine their properties precisely. We show by computation that, adding the inductor to the sample improves the resolution of the DLTS measurement, separates the peaks and facilitates determining accurate values of Ea; s; and N: Finally, the use of light was found to maintain the DX centres deionized, thus keeping the capacitance at reverse bias rather constant which, in turn, enabled us to easily achieve exact resonance conditions for the best effect. q 2003 Elsevier Science Ltd. All rights reserved.