Recombination and Metastability in Amorphous Silicon and Silicon Germanium Alloys: Annual Subcontract Report, 1 February 1991 - 31 January 1992

This report describes the first year of a continuing research study to understand how recombination, trapping, and band-mobility modification affecting the electronic properties of amorphous semiconductors can be measured, characterized, and described by an appropriate spectrum of defect states, and how light-induced defects in a-Si:H and native defects in a-SiGe:H affect transport properties inthese materials. The objective was to determine how the Staebler-Wronski defects affect the electronic processes in a-Si:H and a-SiGe:H films. To do this, electroluminescence (EL) and forward bias current in p-i-n devices (i-layer thickness > 2 um) were studied both experimentally and theoretically before and after light soaking. A simple picture was developed to compare forward bias current tothe EL signal. The result was unexpected: the product of the final current times the rise time was not constant before and after light soaking as expected from the concept of gain band width, but instead changed radically. The rise time tx increased by more than one order of magnitude while the final current It did not change significantly with light soaking. On the other hand, the IfTx productdid hold close to a constant when only the applied voltage changed.