VISIBLE PHOTOLUMINESCENCE FROM POROUS A-SI-H AND POROUS A-SI-C-H THIN-FILMS

We report on the influence of doping, temperature, porosity, band gap, and oxidation on the photoluminescence (PL) properties of anodically etched porous a-Si:H and a-Si:C:H thin films. Only boron-doped, p-type a-Si:H samples exhibited visible photoluminescence. Two broad PL peak s at similar to 1.6 and similar to 2.2 eV are apparent in room tempera ture PL spectra. The intensity of the 2.2 eV peak as well as the nanov oid density in the unetched a-Si:H layers both correlate well with bor on concentration. We see evidence of discrete defect or impurity level s in temperature-dependent luminescence measurements, where we observe multiple luminescence peaks. Unlike in porous crystalline silicon, th e luminescence energy in porous amorphous silicon does not change with porosity. We do, though, observe a correlation of luminescence energy with band gap of the starting a-Si:C:H films. Oxidation, either nativ e or anodic, reduces photoluminescence intensity. We discuss the impli cations of these observations on the nature of the luminescence mechan ism. (C) 1997 American Institute of Physics.