Study on the growth mechanism of hydrogenated amorphous silicon films by infrared reflection absorption spectroscopy

Due to its non-equilibrated nature, hydrogenated amorphous silicon (a-Si:H) varies its properties depending on the preparation conditions. A precise control of its growth process based on the full understanding of its growth mechanism is thus important to make its properties best desired for each specific application such as large-area solar cells and thin film transistors.;In this work, the growth mechanisms of the a-Si:H films are investigated by use of real time in-situ infrared reflection absorption spectroscopy (IR-RAS). The polarization modulation technique is employed to detect the film absorptions on a metal substrate (typically Al) separately from the isotropic gas phase absorptions. Isotope exchange technique is also employed successfully to detect the monolayer hydrogen coverage on the growing surface.;With increasing the film growth temperature from 25°C to 500°C, the dominant bonding configuration of surface hydrogen is found to shift from higher to lower, namely, tri-hydride (SiH3), di-hydride (SiH2) and then mono-hydride (SiH). At higher growth temperature (typically above 400°C) thermal desorption of surface hydrogen is evidenced by the decrease in the absorption intensity of the surface hydrogen observed after the growth. The growth rate of the a-Si:H film is found to increase at the same temperature region. This behavior is explained by an enhancement of surface reactivity induced by the thermal desorption of surface covering hydrogen that is considered to passivate the growing surface. Additional information obtained by IR probe including the precise determination of monosilane partial pressure and the reactions between the substrate and a-Si:H film is also presented.