Solar Cells, 27 (1989) 357 - 362 357 ELECTRON TRAPPING AND PARAMAGNETIC DEFECT DENSITY MEASUREMENTS IN HYDROGENATED AMORPHOUS SILICON S. P. HOTALING, HOMER ANTONIADIS and E. A. SCHIFF Department of Physics, Syracuse University, Syracuse, NY 13244-1130 (U.S.A.) Summary Electron deep-trapping mobility-lifetime (/~r)products were measured in a series of hydrogenated amorphous silicon (a-Si:H) specimens using the transient photocurrent charge-collection technique. A logarithmic depen- dence of the resulting /~r estimate upon the collection time was observed. The correlation of/~r with independent electron spin resonance spectroscopy determinations of the D o defect density AT, was studied. The data are roughly distributed as /~r ~ N, -~ for specimens prepared from pure silane at varying deposition temperatures. The correlation supports the proposal of Street that the predominant deep trap for electrons is the D o defect. I. Introduction An understanding of photocarrier processes is essential for the develop- ment of adequate models for the performance of a solar cell or indeed of any photoelectronic device. For hydrogenated amorphous silicon (a-Si:H) a com- plete understanding has not yet been achieved. Immediately after photo- generation it is generally accepted that both electron and hole evolution may be described by bandtail multiple-trapping, which involves capture of photo- carriers by localized bandtail states and subsequent thermal emission to a transport edge [1]. At later times there is relatively little agreement among researchers, but one remarkably simple conclusion was reached by Street [2], who proposed that both electrons and holes are deep-trapped predom- inantly onto the D O defect observed by electron spin resonance (ESR) spectroscopy. This model is extremely important, as a great deal is known about deep levels in a-Si:H from a variety of optical [3] and space-charge spectroscopies [4]. In this paper, first, the charge-collection experiment which led Street to his conclusion is described. A critical discussion is then presented of the experimental evidence for deep-trapping of electrons by the D o defect, including experimental results which address ambiguities in the earlier charge-collection experiment and which extend the range of Street's experiment. It is concluded that these refinements do not significantly alter Street's conclusion: the D O defect is the dominant electron trap at inter- mediate times. 0379-6787/89/$3.50 © Elsevier Sequoia/Printed in The Netherlands