Chemical bonds and spin properties of a-Si/sub x/Ge/sub y/:H/sub z/ alloys

International audienceHydrogenated amorphous silicon-germanium alloy's are considered important low band gap materials for thin film solar cell technology, but the dangling bond densities increase with the germanium content to prohibitive values. The authors report on IR and electron spin resonance spectra and show some relationships between the preferential attachment of hydrogen, the dangling configurations and the preparation conditions in the plasma. They discuss the g values using the theoretical model proposed by Ishii (1982) for such binary alloys. These values and the peak-to-peak linewidth Delta H deduced from derivative absorption curves exhibit a strong modification with the germanium content of the local environment of the dangling bond. They confirm that a moderate substrate temperature and a high dilution of the reactant gases in hydrogen lead to better alloys

Effect of substrate temperature and deposition rate on the photoconductivity of sputtered a-Si : H

The variation of the photoconductivity versus photon energy is reported for samples deposited at 150 °C, 190 °C and 250 °C at low (30 Å/min.) and high (∼ 150 Å/min.) deposition rates. The spin densities of the same samples are also reported. Taking into account the hydrogen concentration and distribution in these samples, a model according to the photoconductivity is mainly limited by the density and depth of shallow traps originating from hydrogen independent matrix defects is proposed.La variation de la photoconductivité en fonction de l'énergie des photons a été étudiée pour des échantillons produits à 150 °C, 190 °C et 250 °C à faible (30 Å/min.) et grande (∼ 150 Å/min.) vitesse de dépôt. De plus, les densités de spins ont été étudiées. Prenant en considération la concentration et la distribution de l'hydrogène, nous proposons un modèle selon lequel la photoconductivité est principalement limitée par la densité et la profondeur de pièges peu profonds provenant de défauts matrice non compensés par l'hydrogène

Gap state studies in a-Si/sub 1-x/Ge/sub x/:H alloys

The changes in gap state density with increasing Ge concentration in glow-discharge a-Si/sub 1-x/Ge/sub x/:H alloys prepared under well controlled conditions are investigated by analyzing the optical transmission and photothermal deflection measurements. The results are correlated with those of electron spin resonance experiments. A model is proposed for the defect state density

Study of hydrogen configurations by infrared spectroscopy, effusion and nuclear analysis in A-Si/sub x/Ge/sub y/H/sub z/ alloys

International audienceInfrared spectroscopy, thermal effusion, and nuclear analysis were used to perform a systematic investigation of hydrogen incorporation and types of bonding in glow discharge deposited a-Si/sub x/Ge/sub y/H/sub z/ thin films. The study is focused on samples with a low germanium content corresponding to an optical gap EO4 varying between 1.9 eV (a-SiH) and 1.6 eV (35% Ge). From infrared measurements the authors deduce the preferential attachment of hydrogen on Si or Ge atoms and the presence of polysilanes groups, according to the deposition conditions. They also propose a quantitative correlation between (SiH/sub 2/)n (n>or=1) concentrations deduced from IR stretching bands (2080-2090 cm/sup -1/) and weakly bonded hydrogen measured by thermal effusion

Gap state studies in a-Si/sub 1-x/Ge/sub x/:H alloys

The changes in gap state density with increasing Ge concentration in glow-discharge a-Si/sub 1-x/Ge/sub x/:H alloys prepared under well controlled conditions are investigated by analyzing the optical transmission and photothermal deflection measurements. The results are correlated with those of electron spin resonance experiments. A model is proposed for the defect state density