Modified Optically Detected Magnetic Resonance Technique for Studies of Defects in Si and GaAs
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MODIFIED OPTICALLY DETECTED MAGNETIC RESONANCE TECHNIQUE FOR STUDIES OF DEFECTS IN Si AND GaAs W.M. CHEN* AND B. MONEMAR*,** *Department of Physics and Measurement Technology, Link6ping University, S581 83 Link6ping, SWEDEN "**Present address: Max-Planck-Institut fur Festkorperforschung, Heisenbergstrasse 1, D-7000 Stuttgart 80, FRG. ABSTRACT We discuss one of the major difficulties, namely the strong free carrier induced background signal, in studies of defects in Si and GaAs by optically detected magnetic resonance (ODMR) technique. A modified ODMR technique, namely delayed ODMR, is presented and is shown to be very successful in overcoming this difficulty. INTRODUCTION ODMR has been proven to be a powerful technique for studies of electronic structure and microscopic identification of defects in many semiconductors over the past decade [1,2]. However, the application of the ODMR technique to the technologically important materials Si and GaAs as well as their related heterostructures has unfortunately been very limited so far [3-8]. In this work, we wish to expose one of the major difficulties responsible for this limitation, and we also present a modified ODMR technique which successfully overcomes this problem. DIFFICULTIES IN ODMR STUDIES OF DEFECTS IN Si AND GaAs: ORIGIN AND CONSEQUENCE One of the major problems in ODMR studies of defects in Si and GaAs is the presence of a strong background signal [9-15]. This background signal often dominates in an ODMR spectrum and obscures any possible detection of defectrelated ODMR signals, as shown in the upper part of Fig.1. The origin of this background signal has been a great concern, and has been discussed to be manifold [9-15], closely related to the properties of the materials. Some obvious differences between the materials like Si and GaAs and other materials in which ODMR has been very successful include the dielectric constant and the free-carrier mobility. A Si or GaAs crystal with a higher dielectric constant disturbs the microwave (MW) pattern more when placed in a MW cavity. This results in a strong effect on the crystal by a non-vanishing MW electric field (Efield), which should not be the case in an ideal ODMR experiment. Furthermore, free carriers of higher mobility in Si and GaAs are much easier to accelerate and consequently heated in the MW E-field as a cause of MW power loss. The heating of carriers varies the density of electronic excitations localized at defects (e.g. bound exciton (BE)) and thereby affects defect-related PL emission, via altering the capture probability of free carriers by defects or impact ionizing these electronic excitations Mat. Res. Soc. Symp. Proc. Vol. 163. (1990 Materials Research Society
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Fig. 1 (a) Cz-Si:S
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Cz-grown Si, with TL = 0.3 ms, T"d= 0.4 ms,tMw = 0.4 ms and T = 2 ms; Sand (b) from the deep triplet center
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