Showing papers by "Baojie Yan published in 1997"

Defect structure and conductivity in tetrahedrally coordinated metal chalcogenide amorphous semiconductors

Abstract: We examined the paramagnetic defects and the electrical conductivity mechanisms in thin films of amorphous ${\mathrm{Cu}}_{6}{\mathrm{As}}_{4}{\mathrm{S}}_{9}$ deposited using rf sputtering. Electron-spin-resonance (ESR) measurements show that the defects are mainly sulfur dangling bonds. The ESR spin density is independent of temperature, a fact that suggests that the effective electron-electron correlation energies are positive for these defects. Additional ESR centers can be created by optical excitation at low temperatures. These optically induced centers anneal at temperatures above about 100 K. The electrical conductivity scales with the ESR spin density. Transient, optically induced changes in the photoconductivity and the dark conductivity are accompanied by similar transient, optically induced changes in the ESR. These results provide strong experimental evidence that the transport mechanism is controlled by S-dangling-bond defects that supply holes to the valence band for transport.

Electron Spin Resonance of Hydrogenated Amorphous Silicon Alloyed with Sulfur

Abstract: Electron spin resonance (ESR) and light-induced electron spin resonance (LESR) measurements were performed on sulfur-doped hydrogenated amorphous silicon (a-SiS:H). At low S doping levels (H{sub 2}S/SiH{sub 4} {le} 10{sup {minus}3} in gas phase), the ESR and LESR line shapes are similar to those observed in undoped a-Si:H. The dark spin density generally increases with S doping and reaches 5 x 10{sup 16} cm{sup {minus}3} at H{sub 2}S/SiH{sub 4} {approx} 10{sup {minus}3}. On the other hand, at high S concentration, the dark spin density increases significantly with S concentration. The ESR and LESR line shapes become identical and asymmetric, a fact that implies the ESR and LESR signals result from the same kind of ESR center. Since S doping is very inefficient, the ESR signals probably are due to defects instead of trapped carriers in band tails. The asymmetry of the ESR and LESR line shapes at high sulfur concentration may result from either more than one type of defect or an asymmetry in the g tensor of a single defect. The photo-excitation of H-passivated, S-related defects could also contribute to the LESR.

Light induced effects in a-Si:H films alloyed with sulfur

Abstract: Light-induced effects are studied in hydrogenated amorphous silicon-sulfur alloys (a-SiS{sub x}:H) and compared to those that exist in a-Si:H. The A-SiS{sub x}:H films were grown by decomposition of pre-mixtures of SiH{sub 4} and H{sub 2}S. The light-induced effects were monitored using electrical (dark conductivity and photoconductivity, including the constant photocurrent method [CPM]) and optical (photoluminescence) measurements and electron spin resonance. It is found that sulfur alloying results in a significant reduction in the degradation in the dark- and photo-conductivity. For an a-SiS{sub x}:H film grown with a gas mixture of H{sub 2}S/SiH{sub 4} = 0.02, there is an increase of over an order of magnitude in the dark conductivity and a small decrease in the photoconductivity after 50 hours of light soaking. The subgap deep defect density as measured by CPM increases with illumination time, following a stretched exponential to saturation. The saturated defect density is an order of magnitude higher than that observed in the annealed state.