Light-emitting properties of amorphous Si:C:O:H layers fabricated by oxidation of carbon-rich a-Si:C:H films

摘要

Amorphous hydrogenated carbon-rich silicon-carbon alloy film (a-Si_(0.3C_(0.7): H) was deposited by reactive dc-magnetron sputtering of silicon target in argon-methane gas mixture. As-deposited film exhibits white photoluminescence at room temperature. After the deposition the samples were thermally annealed in dry Ar, wet Ar, or dry O_2 flow at 450 deg C for 30 minutes that resulted in the enhancement of the photoluminescence intensity by a factor of about 5, 8 and 12 respectively. Spectral distribution of light emission was almost unchanged at the annealing in dry and wet argon while the oxidation in pure oxygen resulted in strong enhancement of a "blue" shoulder in the spectrum. EPR measurements at room temperature showed the decrease of spin concentration after thermal treatment in dry and wet argon and no EPR signal was detected after annealing in oxygen. FTIR and XPS measurements evidenced the formation of a-Si:O:C:H composite material after dry oxidation. Based on the measurements of photoluminescence in the temperature range 7-300 K it is suggested that light-emitting efficiency of a-Si_(0.3)C_(0.7): H is determined by migration of the photo-excited carriers to non-radiative recombination centers. The physical mechanisms that can be involved in the strong enhancement of visible photoluminescence in Si:C:O:H layers are discussed.