PHOTOLUMINESCENCE CHARACTERIZATION OF A-SI1-XCX - H ALLOYS PREPARED BY COSPUTTERING

We have characterized a-Si1-xCx:H films (0 less-than-or-equal-to x les s-than-or-equal-to x 0.99) prepared by cosputtering of separated carbo n and silicon targets using continuous-wave (cw) and time-resolved pho toluminescence. A fast analog technique with a time resolution of 100 ps was used for time-resolved measurements. We have analyzed the decay s in terms of a model function, with which the experimental time broad ening is removed by deconvolution. The model function is given by I(t) =a0 + SIGMA(i=1)n a(i) exp(-t/tau(i)), where a0, a(i), and tau(i) are the fitting parameters. The fits with this model yield three dominatin g lifetimes tau(1) = 0.8 +/- 0.2 ns, tau2 = 3.5 +/- 0.6 ns, and tau3 = 14.5 +/- 2.5 ns for 0 < x less-than-or-equal-to 0.65. We proposed an excitonic origin for these three processes and suggest that they are c onnected with some short-range aspects of the a-Si:H network. For the film with highest carbon content (x = 0.99), we get two shorter lifeti mes with tau1 = 0.36 +/- 0.1 ns and tau2 = 1.1 +/- 0.1 ns, and attribu te them to a major structural change in the network.