AVS 45th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM9
Growth of Si@sub 1-x@Ge@sub x@ on Si(011): Kinetics, Surface Structure, and Morphological Evolution

Wednesday, November 4, 1998, 11:00 am, Room 308

Session: Physics of Semiconductors
Presenter: N. Taylor, University of Illinois, Urbana-Champaign
Authors: N. Taylor, University of Illinois, Urbana-Champaign
H. Kim, University of Illinois, Urbana-Champaign
T. Spila, University of Illinois, Urbana-Champaign
P. Desjardins, University of Illinois, Urbana-Champaign
J.E. Greene, University of Illinois, Urbana-Champaign
Correspondent: Click to Email
Strained Si@sub 1-x@Ge@sub x@/Si(011) heterostructures provide additional degrees of freedom over the more common Si@sub 1-x@Ge@sub x@/Si(001) system for bandgap engineering. The maximum film/substrate conduction band offset is predicted to be substantially larger, the optical bandgap decreases more rapidly with increasing x, and optical selection rules allow hole-intersubband transitions to be excited by light parallel to multiple quantum well layers. In this investigation, Si@sub 1-x@Ge@sub x@ layers with x @<=@ 0.35 were grown on Si(011) by gas-source molecular beam epitaxy (GS-MBE) using Si@sub 2@H@sub 6@ and Ge@sub 2@H@sub 6@ at T = 400-950 °C. The growth kinetics are a function of the following complex surface reconstructions: 16x2 at x < x@sub c@ and 2x8 at x > x@sub c@. The critical Ge concentration x@sub c@ ranges from 0.10 at T = 475 °C to 0.06 at T = 650 °C. As the temperature is raised from 650 to 725 °C, the surface gradually transforms to a 1x1 reconstruction for all x. Temperature-programmed desorption (TPD) measurements show that the 16x2 unit cell consists of 16 adatoms and 8 pi-bonded dimers, resulting in 32 dangling bonds compared to 64 for the 1x1 surface. In the surface-reaction-limited growth mode at T < 500 °C, the rate-limiting growth step is hydrogen desorption from the Si and/or Ge monohydride. The surface structure consists of uniformly-sized terraces, according to atomic force microscopy (AFM) measurements. In the flux-limited regime at T = 500-650 °C, the growth rate is limited by the surface-dependent reactive sticking coefficient and the morphology is characterized by extensive faceted pitting. At T > 650 °C, the growth rate rises with temperature as the dangling bond coverage increases with the surface transformation to a 1x1 reconstruction. At these high temperatures, the surface morphology consists of long ridges oriented along the [100] direction.