Density of states in tritiated amorphous silicon obtained with the constant photocurrent method

Abstract

The constant photocurrent method was implemented to determine the density of states in tritiated hydrogenated amorphous silicon below the Fermi level. The tritiated hydrogenated amorphous silicon samples were grown using a mixture of silane and tritium gases in the dc saddle-field deposition system. Over time the tritium incorporated in the amorphous silicon undergoes beta decay and transmutation into helium. The transmutation leads to an increase in the density of states in the energy gap of the material. These states are linked to silicon dangling-bond defects. Given its well-characterized decay process, tritium can be used as an experimental tool to study the behavior of hydrogenated amorphous silicon thin films as a function of their defect state density. The density-of-states information in this work indicates a dominant peak of doubly occupied dangling bonds (D−) positioned 1.24eV below the conduction band. The defect density was monitored in time showing an increase of more than two orders of magnitude over a period of 20days and a decrease of similar magnitude upon thermal annealing.