Static versus electron-phonon disorder in amorphous Si: H and its alloys

We present new results from photoluminescence studies of a-Si: N: H alloys which enable us to distinguish between the effects of rigid-band (i.e. static) and electron-phonon disorder. Using predictions of correlations between the M-band width, the Urbach slope and the Tauc gap, we show that static structural disorder determines the photoluminescence band width. Analysis of earlier work on the a-Si: C: H and a-Si: Ge: H systems supports these conclusions. By using subgap excitation of luminescence, we provide further evidence that in the nitrogen-rich alloys this disorder is predominantly due to long-range alloy compositional fluctuations.