Characterization of Si-rich a-Si1-xNx : H alloys deposited by laser-CVD

Highly silicon-rich amorphous hydrogenated silicon nitride (a-Si1-xNx:H) al loys (0.11 < x < 0.34) were prepared by ArF laser-induced photolysis perfor med in parallel configuration using Ar-buffered disilane/ammonia gas mixtur es. The combined W-induced photodissociation of both precursor gases genera tes high growth rates in the range of 0.3 to 0.7 nm s(-1) whose dependencie s on the substrate temperature (200-400 degrees C) and the percentage of di silane in the gas mixture are presented. While the growth rate increases ex ponentially with the temperature, its variation with the decreasing disilan e content shows an initial decrease followed by sharp increase at a critica l precursor gas composition and subsequent decrease for gas mixtures having very low disilane content. Films have been analysed by Fourier transform i nfrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), profilom etry and UV spectroscopy. The band gap measurements reveal that these silic on-rich films with compositions below the percolation threshold of Si-Si bo nds (i.e., x < 0.52) show fine band gap controllability in the range of 1.6 to 2.9 eV. The band gap value seems to be directly linked to the bonded hy drogen content and to have low sensitivity to variations in the nitrogen co ntent. (C) 1999 Elsevier Science B.V. All rights reserved.