Characterization of the Visible Photoluminescence from Porous a-Si:H and Porous a-Si:C:H Thin Films

We report on the influence of doping, temperature, porosity, and bandgap on the visible photoluminescence properties of anodically-etched porous a-Si:H and a-Si:C:H thin films. Only boron-doped, p-type a-Si:H or a-Si:C:H samples exhibited any visible photoluminescence. We see evidence of discrete defect or impurity levels in temperature-dependent luminescence measurements. Unlike in porous crystalline silicon, we see no correlation of luminescence energy with porosity. We do, though, observe a correlation of luminescence energy with bandgap of the starting a-Si:C:H films. We discuss the implications of these observations on the nature of the luminescence mechanism.