Nanocavities in silicon: an infrared investigation of internal surface reconstruction after hydrogen implantation

The preparation of tetrakaidecahedron-shaped nanocavities in silicon via thermal treatments of high fluence helium-implanted silicon is a well established process. When the mean distance between such cavities is on the length scale of the exciton diameter, they are expected to modulate the silicon band structure. This property, however, can hardly be exploited due to the large number of dangling bonds remaining on the cavity inner surface at the end of the process. An easy way to reduce their amount is to passivate them with hydrogen. To investigate the interaction of hydrogen with (i) bulk silicon and (ii) the inner surface of the nanocavities, hydrogen was implanted in silicon on preformed nanocavity arrays and the evolution of the Si H complexes after isochronal annealings in the temperature range 150–800 °C was sensed by infrared spectroscopy in multiple internal reflection geometry. In contrast with previous findings, we will provide evidence that there is no measurable redistribution from bulk defects to inner surface during the thermal treatments. Thus, within the limits of experimental sensitivity, surface passivation was proved to occur upon implantation. Annealing eliminates first the most reactive species (SiH3 and SiH2 above 500 and 550 °C, respectively); at higher temperatures only signals related to the remaining H passivation of the ideal reconstructed H (1 x 1)–Si(1 1 1), H (7 x 7)–Si(1 1 1), and H (2 x 1)–Si(1 0 0) surfaces are observed.