Effects of microwave power on the structural and emission properties of hydrogenated amorphous silicon carbide deposited by electron cyclotron resonance chemical vapor deposition

Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films have been deposi ted using an electron cyclotron resonance chemical vapor deposition system. The effects of varying the microwave power from 100 to 1000 W on the depos ition rate, optical band gap, film composition, and disorder were studied u sing various techniques such as Rutherford backscattering spectrometry, spe ctrophotometry, Fourier-transform infrared absorption, and Raman scattering . Samples deposited at 100 W are found to have a carbon fraction (x) of 0.4 9 which is close to that of stoichiometric SiC, whereas samples deposited a t higher microwave powers are carbon rich with x which are nearly independe nt of the microwave power. The optical gaps of the films deposited at highe r microwave powers were noted to be related to the strength of the C-H-n bo nd in the films. The photoluminescence (PL) peak emission energy and bandwi dth of these films were investigated at different excitation energies (E-ex ) and correlated to their optical band gaps and Urbach tail widths. Using a n E-ex of 3.41 eV, the PL peak energy was found to range from 2.44 to 2.79 eV, with the lowest value corresponded to an intermediate microwave power o f 600 W. At increasing optical gap, the PL peak energy was found to be blue shifted, accompanied by a narrowing of the bandwidth. Similar blueshift was also observed at increasing E-ex, but in this case accompanied by a broade ning of the bandwidth. These results can be explained using a PL model for amorphous semiconductors based on tail-to-tail states radiative recombinati on. A linear relation between the full width at half maximum of the PL spec tra and the Urbach energy was also observed, suggesting the broadening of t he band tail states as the main factor that contributes to the shape of the PL spectra observed. (C) 2001 American Institute of Physics.