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

Abstract

Hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effects of varying the microwave power from 100 to 1000 W on the deposition rate, optical band gap, film composition, and disorder were studied using various techniques such as Rutherford backscattering spectrometry, spectrophotometry, Fourier-transform infrared absorption, and Raman scattering. Samples deposited at 100 W are found to have a carbon fraction (x) of 0.49 which is close to that of stoichiometric SiC, whereas samples deposited at higher microwave powers are carbon rich with x which are nearly independent of the microwave power. The optical gaps of the films deposited at higher microwave powers were noted to be related to the strength of the C–Hn bond in the films. The photoluminescence (PL) peak emission energy and bandwidth of these films were investigated at different excitation energies (Eex) and correlated to their optical band gaps and Urbach tail widths. Using an Eex 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 of 600 W. At increasing optical gap, the PL peak energy was found to be blueshifted, accompanied by a narrowing of the bandwidth. Similar blueshift was also observed at increasing Eex, but in this case accompanied by a broadening of the bandwidth. These results can be explained using a PL model for amorphous semiconductors based on tail-to-tail states radiative recombination. A linear relation between the full width at half maximum of the PL spectra and the Urbach energy was also observed, suggesting the broadening of the band tail states as the main factor that contributes to the shape of the PL spectra observed.