Complex Defects in Semiconductors
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COMPLEX DEFECTS IN SEMICONDUCTORS B. MONEMAR' Max-Planck-Institut ffir Festk6rperforschung Heisenbergstr. 1, D-7000 Stuttgart 80, Federal Republic of Germany
ABSTRACT
Complex defects in semiconductors are briefly reviewed, with emphasis on the electronic structure. Classes of such defects with a varying degree of complexity are discussed, with reference to recent optical data for neutral defects in GaP and silicon. These include PG.antisite related substitutional complexes in GaP, Gai-acceptor complexes in GaP, substitutional chalcogen complex defects in silicon and vacancy-impurity complexes in silicon.
I. INTRODUCTION The importance of defects in determining relevant properties of semiconductors was realized at an early stage, and already in the 1950's a considerable amount of work was carried out on defect characterization, in particular concerning shallow dopants. Ever since there has been a steady increase in the activity in this research area, and most physical aspects of shallow impurities are now understood, at least on a practical level. [1] The more detailed studies of deep levels in semiconductors started later (in the 1960's and 1970's), but a great deal of progress has been done, particularly on point defects. [2] There is another class of defects, however, where progress has been much slower, namely complex defects, which typically consist of more than one defect site, and have a low symmetry. [3] Such defects commonly occur in most semiconductors, particularly as a result of various processing steps, and are of practical importance as residual defects that very significantly affect various properties like carrier recombination, lifetimes and degradation behavior. The problems of calculating properties of such defects from first principles with a sufficient accuracy are not yet commonly addressed, although a few cases have been attempted. [4,5,6] Experimentally there are two major pieces of information to be extracted in order to obtain a satisfactory understanding of complex defects: (a) the identity of the defect, i.e. the local geometrical arrangement of the atoms participating in the defect structure, and (b) the electronic structure of the defect, i.e. the bound electronic states and their properties. The first problem seems to be a real bottleneck, since there are, so far, no generally applicable techniques developed with a sufficient sensitivity to selectively study the structure of a specific complex defect, which is often of lower concentration than other defects (or impurities) in the material. Recent advances on this problem will be exemplified below. The electronic structure can in many cases be studied with optical perturbation spectroscopy [3,7], including the recently developed optically detected magnetic resonance (ODMR) technique. [8,9] This paper summarizes briefly some recent developments in the study of physical properties of complex defects, with emphasis on the electronic structure. Different classes of complex defects are briefly discussed, demonstrating the degree of complex
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