Recombination Activity of Individual Extended Defects in Silicon
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RECOMBINATION ACTIVITY OF INDIVIDUAL EXTENDED DEFECTS IN SILICON A. Cavallini and A. Castaldini University of Bologna, Dept. of Physics,Via Imerio 46, 1-40126 Bologna, Italy.
ABSTRACT Dislocations and point defects introduce energy levels deep in the gap, which dramatically change the material electrical properties. Because of the coexistence of a multitude of dislocation types and dislocation-point defect interaction mechanisms, it would be highly desirable to identify the particular type of defect related to specific traps. The electrical activity of extended defects (planar precipitates and dislocations) is here examined in terms of their recombination activity, investigated by electron as well as light beam induced current methods of scanning microscopy. Besides, a scanning modification of spectroscopy is used to identify traps at individual defects. The method, named quenched infra-red beam induced current, combines the scanning light beam induced current technique with the spectroscopic bulk analysis called "infrared quenching of photoconductivity". Defect energy levels are found on the basis of the particular features of the beam induced current as a function of injected carrier generation rate, temperature and quenching excitation. INTRODUCTION In recent years scanning microscopy in charge collection mode (CCSM) experienced a significant change in the way of referring to defects which present recombination activity. At the very beginning, the defects have been dealt with like a "black box", whose interesting features were spatial arrangement and strength (recombination velocity) y deduced by the contrast c, defined as equal to the difference AI in current collected when the beam crosses the defect (Id)and measured in the bulk far from the defect (L ), normalized to Ib. More recently a few models [1-4] have been presented which, relating the electrical properties of defects to their electronic states in the band gap, try to understand the particular features of the structure of dislocations and, more generally speaking, extended defects at which the electronic states are located. Following this latter trend, the purpose of the present paper is to report on recombination activity of planar copper silicide precipitates in p-Si, for which a number of clear conclusions can be drawn. The second part of this paper is devoted to our first results on electronic states at dislocations introduced by deformation in n-Si, investigated at low carrier injection conditions. For this aim, scanning electron and optical injection has been used to excite electrons and holes in semiconductors, and the generated current has been measured. By scanning the beam over the semiconductor, an image can be obtained of the regions where there is strong or weak electron-hole recombination. In the present paper the recombination has been measured as a function of injection level, temperature and spatial arrangement of the defects. In addition, secondary excitation of electronic levels has been used to determine localized energy levels. Ma
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