The density of states of sputtered a-Si: H studied by the space-charge-limited current technique The influence of deposition parameters, light and keV-electron irradiation

Abstract

The space-charge-limited current (SCLC) technique has been used to determine the density of states (DOS) near the Fermi level for a-Si: H films prepared by magnetron sputtering under various experimental conditions. From a study of the thickness dependence it can be concluded that surface or interface states might significantly contribute to the DOS. A minimum DOS of 5⋅5 × 10¹⁵ cm⁻³ eV⁻¹ at E _c — E = 0⋅75 eV was determined for well passivated films. The generation of metastable defects by light soaking and keV electron irradiation has been directly observed by the change in the DOS. For the same energy deposited, defect creation by electrons is a factor of 3300 higher than that by light. In addition, the generation process is found to be different. A model is suggested that explains the creation of defects by electrons via a direct electronic excitation process.