Phosphorus incorporation during silicon(001):phosphorus gas-source molecular beam epitaxy: Effects on film growth kinetics, surface morphology, and the self-organization of germanium quantum dot overlays.

摘要

The effects of P doping on growth kinetics and surface morphological evolution during Si(001):P gas-source molecular-beam epitaxy from Si 2H6 and PH3 at temperatures Ts = 500-900°C have been investigated. With increasing PH3/Si2H 6 flux ratio JP/Si at constant Ts, I observe a decrease in the film growth rate R and an increase in the incorporated P concentration CP, both of which tend towards saturation at high flux ratios, accompanied by increased surface roughening and pit formation. I use in-situ isotopically tagged D2 temperature programmed desorption (TPD) to follow changes in film surface composition and dangling bond density thetadb as a function of JP/Si and T s. The steady-state P surface coverage thetaP reaches a maximum value of ∼1 ML at Ts = 550°C, and decreases with Ts > 600°C due to the onset of P2 desorption. Comparison of thetaP(Ts) with CP(Ts) results obtained during film growth reveals the presence of strong P surface segregation, with a P segregation enthalpy DeltaHs= -0.86 eV. Using the combined set of results, I develop a predictive model for CP vs. T s and JP/Si, incorporating the dependence of the PH 3 reactive sticking probability SPH3 on thetaP, which provides an excellent fit to the experimental data.; I build upon these results to understand the effect of growth rate and P predeposition on Ge/Si(001) island geometry, density, and spatial distributions. Ge quantum dots are deposited on three types of starting surfaces: (1) Si(001) buffer layers which serve as a reference, (2) Si(001) layers with predeposited P coverages thetaP ranging from 0 to 1 ML, and (3) P-doped Si(001) with CP = 3.4x1018-8.3x10 18 cm-3, which corresponds to thetaP = 0.5-0.8 ML. Predeposited P passivates and roughens the Si(001) surface, which inhibits surface diffusion and causes an increase in Ge island density and pyramid-to-dome ratio, accompanied by enhanced island self-organization along 100> directions.