Effect of H on Si molecular-beam epitaxy

Abstract

In Si crystal growth by molecular-beam epitaxy (MBE) at low temperatures there is known to be an epitaxial thickness: an initially crystalline regime before the deposited film becomes amorphous. The predominant impurity in MBE is hydrogen, but the role of background H in low-temperature MBE has not previously been assessed. Here the effect of deliberate dosing of the Si surface with atomic H during low-T growth is studied. The epitaxial thickness is shown to be sensitive to very small additional H fluxes (≊10−9 Torr, i.e., an increase in H only marginally above ambient). With further increases in dose rate, the epitaxial thickness decreases as hepi=h0−k(ln PH). Using secondary-ion-mass spectrometry data on the segregated H at the interface, we argue that breakdown in epitaxy is not caused directly by the surface concentration of adsorbed impurities. It is deduced that very small concentrations of H may influence the Si surface diffusion rate. The possible effect of background H adsorption on previous experiments on Si steps and surface diffusion is discussed.