Role of SiH2 in 1H Nmr of μc-Si:H Deposited with Different Plasma Excitation Frequencies and Silane Concentrations

Abstract

AbstractPrevious lH NMR and IR studies of six samples of μc-Si:H prepared under plasma excitation frequencies ranging from 13 MHz to 95 MHz and silane concentrations ranging from 3% to 8% revealed three important results: (1) for a fixed plasma excitation frequency (95 MHz) the hydrogen content increases with silane concentration; (2) for fixed silane concentration the hydrogen content is roughly constant over a wide range of plasma excitation frequencies; and (3) the 1H NMR free induction decay exhibits beat frequencies which correspond to the calculated frequencies due to SiH2 in microcrystalline silicon. In this study we investigate the role of SiH2 in the μc-Si:H structure using 1H NMR measurements. We studied two samples prepared at two different plasma excitation frequencies (13 MHz and 95 MHz). The lU NMR lineshapes of these samples were measured at 300 K and 77 K. The motionally narrowed component of the 1H NMR is not as rapid at room temperature as that observed previously, but the linewidth of this component increases significantly at 77 K. Because of this difference between our results and those reported previously, it is possible that H2 molecules are not responsible for the motional narrowing in our samples. We present plausible arguments for the hindered motion of SiH2 groups in our μc-Si:H samples.