Photoluminescence in ultrathin a-Si:H layers

The evolution of photoluminescence characteristics of a-Si:H layers as a function of layer thickness is examined in a variety of sample configurations. These include individual a-Si:H layers de- posited on a-${\mathrm{SiO}}_2$ substrates with native oxide layers, individual a-Si:H layers with plasma-deposited under- and/or overlayers of a-${\mathrm{SiN}}_{\mathrm{x}}$:H, and nitride multilayer structures. Qualitatively, the optical properties of all the samples exhibit the same trends, but there are large quantitative differences which depend on the under- and overlayer materials. The effects due to the two interfaces are not independent, indicating that the nature of the a-Si:H layer itself depends on the composition of the neighboring material. A combination of nitrogen contamination, increased hydrogen content, and disorder can account for all the observed differences in the optical properties.