Influence of hydrogen concentration on void-related microstructure in low hydrogen amorphous and crystalline silicon materials

The influence of implanted hydrogen (up to a concentration level of 3 at. %) on the microstructure of silicon (Si) materials is investigated by Fourier transform infrared spectroscopy as well as by effusion of hydrogen and of (low dose) implanted helium. Three materials of low original hydrogen concentration, crystalline Si, electron beam evaporated amorphous Si, and plasma-deposited hydrogenated amorphous Si (using high deposition temperature) were investigated. Significant differences between crystalline and amorphous materials were observed. In crystalline Si, implanted hydrogen is found to generate multivacancies that trap diffusing helium while this is not the case in amorphous Si. Accordingly, cavities where hydrogen is located in amorphous Si must be smaller than divacancies. Those cavities in amorphous Si, present from the growth process, that trap helium tend to disappear when the implanted hydrogen concentration increases. Annealing of the materials up to temperatures of 575°C was also studied. No significant change in the density of voids (trapping helium) occur but in case of crystalline Si the bonding sites of hydrogen as well as the diffusion paths of helium change. PACS Nos.: 61.43.Dq, 61.72.uf, 81.40.-z. Nous utilisons la spectroscopie infrarouge a transformee de Fourier, l'effusion d'hydrogene (H) et l'implantation d'helium (He; a basse dose), pour etudier l'influence de l'implantation d'H (jusqu'a des concentration de 3 at. %) sur les microstructures de materiaux de silicium. Nous etudions trois de ces materiaux de faible concentration initiale en H, le silicium cristallin, le silicium amorphe evapore par faisceau electronique et le silicium amorphe hydrogene par depot (a haute temperature). Des differences importantes apparaissent entre materiaux cristallins et amorphes. Dans le silicium cristallin, l'H implante cree des multi-lacunes qui piegent l'He en diffusion, ce qui n'est pas le cas pour le silicium amorphe. Consequemment, les cavites ou se trouve l'H dans le Si amorphe doivent etre plus petites que des bi- lacunes. Ces cavites qui piegent l'He dans le silicium amorphe, presentes lors de l'elaboration du materiau, tendent a disparaitre lorsque la concentration de l'H implante augmente. Nous etudions aussi l'effet d'un recuit des materiaux jusqu'il 575°C. Aucun changement significatif de la densite de pieges n'apparait, mais dans le cas cristallin, les sites de capture de H et les trajectoires de diffusion de He changent. [Traduit par la Redaction]
1. Introduction Void-related microstructure is an important issue in hydrogenated amorphous silicon (a-Si:H) technology as it may limit the performance and the lifetime of a-Si:H based devices. The relation between [...]