Characteristics of room temperature bipolar photoconductance in 150 GHz probe transients obtained from normal and irradiated silicon illuminated by 532 nm laser

TL;DR

This study investigates the transient bipolar photoconductance in silicon at 150 GHz, revealing a negative kink in excess conductivity after laser excitation, with implications for defect characterization in irradiated silicon.

Contribution

It presents the first detailed analysis of negative photoconductivity kinks in silicon transients at 150 GHz, comparing pristine and irradiated samples to link defect parameters.

Findings

Negative kink appears after positive decay in silicon transients.

Irradiated silicon shows altered transient characteristics.

Negative photoconductivity lasts approximately 36 microseconds.

Abstract

A negative kink in excess conductivity is observed in p-type non-degenerate (moderate dopant concentration) silicon wafers when excited by a very narrow pulse of 532 nm laser appearing just after the complete positive decay of dark conductivity voltage. Most of the Si samples are pristine, and 3 of them are irradiated with gamma, proton, and chlorine ion beams respectively. These transients were examined using a time-resolved millimeter-wave conductivity apparatus (TRmmWC ) and the radiofrequency (RF) voltage response (after laser cut-off) consistently reveals a positive peak with nominal decay to zero followed by a negative kink. This negative photoconductivity (NPC) kink develops just after the complete decay of the positive photoconductivity (PPC) and lasts typically ~ 36 us. We present some data on general characteristics obtained from a set of normal (pristine doped Si) wafers and the gamma- and ion beam irradiated silicon (comparing with the parent pristine sample responses) for establishing possible new links that might enable estimation of defect parameters introduced in silicon.