Analysis of transient photoconductivity in counterdoped silicon:gold

Abstract

Photoconductive and electrical measurements have been made in the temperature range 77-290K on counterdoped silicon in which a shallow acceptor, boron, is compensated with a deep donor, gold. Analysis of the photoconductive transients, including shallow-level trapping effects, has given a value of 2.4*1014 cm-3 for the density of optically active deep centres, 4.7*10-14 cm2 for their photoexcitation cross section and 1.2*10-19 cm2 for their capture cross section. These results are discussed and compared with those obtained or predicted by other workers. An important feature of the analysis is that significant exhaustion of the deep level occurs at high photon intensities. This large-signal effect has been confirmed experimentally using double-beam techniques. The density of optically active centres is less than two percent of the electrically active density, which was inferred from measurement of room-temperature resistivity and carrier freeze-out at low temperatures. It is concluded, therefore, that there are two deep levels present, one that is predominantly responsible for the electrical compensation of the material and a second of lower density that provides the principal optical response.