Growth of Si1-xGex(011) on Si(011)16x2 by gas-source molecular beam epitaxy: Growth kinetics, Ge incorporation, and surface phase transitions

Single crystal Si1-xGex(011) layers with x less than or equal to 0.35 have been grown on double-domain Si(011) "16 x 2'' surfaces from Si2H6/Ge2H6 mix tures at temperatures T-s = 400-950 degrees C. D-2 temperature programmed d esorption was used to show that the structure of the Si(011) "1632'' surfac e unit cell, more correctly written as [(17)(1)(2 2)] since the unit cell v ectors are nonorthogonal, is composed of 16 adatoms and eight pi-bonded dim ers with a dangling bond density half that of the 1 x 1 surface. Si1-xGex(0 11) overlayers are "16 x 2'' when x < x(c)(T-s) and "2 x 8'' with x > x(c)( T-s). The value of x(c) decreases from similar or equal to 0.10 at T-s = 47 5 degrees C to 0.08 at 550 degrees C to 0.06 at 650 degrees C. Both the "2 x 8'' and "16 x 2'' Si1-xGex(011) surface reconstructions gradually and rev ersibly transform to 1 x 1 at T-s between 650 and 725 degrees C. Film growt h kinetics exhibit three distinct regimes. At low temperatures (T-s less th an or similar to 500 degrees C), the film deposition rate R-SiGe decreases exponentially with 1/T-s in a surface- reaction-limited growth mode for whi ch the rate- limiting step is hydrogen desorption from Si and Ge monohydrid e phases. R-SiGe becomes essentially constant with T-s in the intermediate impingement-flux- limited range, T-s = 500-650 degrees C. At T-s > 650 degr ees C, R-SiGe increases again with T-s due initially (T-s similar or equal to 650-725 degrees C) to an increase in the steady- state dangling bond cov erage as the surface reconstruction gradually transforms to 1 x 1. The cont inued increase in R-SiGe at even higher T-s is associated with strain-induc ed roughening. Ge/ Si ratios in as- deposited films are linearly proportion al to the incident Ge2H6/Si2H6 flux ratio J(Ge2H6)/J(Si2H6) and nearly inde pendent of T-s indicating that the reactive sticking probabilities of Si2H6 and Ge2H6 have very similar temperature dependencies. R-SiGe (J(Ge2H6)/J(S i2H) (6),T-s) in both the surface- reaction- limited and flux- limited regi mes is well described by a simple kinetic model incorporating second- order dissociative chemisorption and second- order hydrogen desorption as rate- limiting steps.