Si1-xGex layers with x ranging from 0 to 0.30 were grown on Si(001)2x1 substrates at temperatures ranging from 450 to 950°C by gas-source molecular-beam epitaxy (GS-MBE) from Si2H6 and Ge2H6. In the low-temperature surface-reaction-limited growth regime, the deposition rate RSiGe increases with increasing Ge concentration due to an enhancement in the hydrogen desorption rate resulting in a correspondingly higher steady-state dangling bond density. In the high-temperature impingement-flux-limited regime, where the steady-state hydrogen coverage approaches zero, RSiGe is controlled by the Si2H6 and Ge2H6 reactive sticking probabilities S which decrease with increasing Ge2H6 flux but are not strongly temperature dependent. SSi2H6 and SGe2H6 range from 0.036 and 0.28 on Si(001) to 0.012 and 0.094 during growth of Si0.82Ge0.18 at Ts = 800°C. In both growth regimes, large changes in RSiGe require only modest increases in incident Ge2H6 to Si2H6 flux ratios, JGe2H6/JSi2H6, due to Ge segregation which is strongly coupled to the steady state hydrogen coverage. The Ge to Si ratio in as-deposited films increases linearly, while SGe2H6/SSi2H6 remains constant, with increasing JGe2H6/JSi2H6. Hydrogen desorption and Ge segregation rates, together with Si2H6 and Ge2H6 reactive sticking probabilities, were quantitatively determined from D2 temperature-programmed desorption (TPD) measurements. The combined results from film growth kinetics and TPD studies, together with the assumption of linear superposition, were then used 10 develop a predictive model, with no fining parameters, for RSiGe(Ts,JSi2H6,JGe2H6) during Si1-xGex GS-MBE.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)