Bombardment-produced disorder and SiH bonds in crystalline and amorphous silicon

Abstract

Hydrogenation of silicon has been investigated under conditions in which lattice disorder and hydrogen concentration are independently controlled. Control of hydrogen concentration and disorder to produce a crystalline-to-amorphous transition was achieved by hydrogen ion implantation and self-ion bombardment, respectively. Hydrogen concentrations and depth distributions were determined by ion-beam-analysis techniques, and infrared absorption was used to measure the SiH stretch modes for chemically bound hydrogen. Hydrogen implanted into crystalline silicon is chemically trapped at the end of its range and introduces numerous Si---H stretch frequencies associated with crystalline defects. Subsequent amorphization by self-ion bombardment causes a coalescence of the SiH stretch modes to a 1985 ${\mathrm{cm}}^{\ensuremath{-}1}$ band which is characteristic of monohydride centers in amorphous silicon. We also find that the presence of hydrogen in silicon stabilizes disorder and reduces the silicon-ion fluence necessary to produce amorphization. Monohydride centers dominate in hydrogenated bombardment-amorphized silicon, but there is evidence for saturation of the monohydride center for concentrations greater than a few percent. Ion bombardment of sputter-deposited amorphous silicon with 3 at.% hydrogen causes a thermally stable transfer of hydrogen from dihydride to monohydride centers. The predominance of monohydride centers and saturation of such centers in silicon amorphized by ion bombardment is consistent with predictions of Phillips's model.