AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM2-ThM

Paper EM2-ThM9
Formation of Flat, Relaxed Si@sub 1-x@Ge@sub x@ Alloys on Si(001) Without the Use of Buffer Layers

Thursday, November 3, 2005, 11:00 am, Room 310

Session: Heteroepitaxy and Low-Dimensional Structures
Presenter: S. Hong, Seoul National University, South Korea
Authors: S. Hong, Seoul National University, South Korea
H.-W. Kim, Seoul National University, South Korea
D.K. Bae, Seoul National University, South Korea
S.C. Song, Seoul National University, South Korea
G.-D. Lee, Seoul National University, South Korea
E. Yoon, Seoul National University, South Korea
C.S. Kim, Korea Research Institute of Standards and Science
Y.L. Foo, University of Illinois at Urbana-Champaign
J.E. Greene, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
Flat, fully-strained Si@sub 1-x@Ge@sub x@ layers with thicknesses ranging from 40 to 240 nm were grown on Si(001) at 450 @super o@C by ultrahigh vacuum chemical vapor deposition and subjected to furnace annealing at 1000 @super o@C for 20 min to induce relaxation. In order to suppress the thermally-activated surface adatom diffusion leading to surface roughening, while simultaneously promoting misfit dislocation formation, SiO@sub 2@ capping layers were deposited prior to annealing. The degree of strain relaxation R and the root-mean-square surface roughness w are determined as a function of layer thickness. For Si@sub 1-x@Ge@sub x@ layers annealed without SiO@sub 2@ cap layers, the primary relaxation mechanism is strain-induced roughening leading to the formation of a self-organized mound structure with high w and R. However, for capped layers, strain-relaxation occurs through the formation of misfit dislocations and surface roughening is controlled by the resulting cross-hatch. Detailed analysis using atomic force microscopy line scans show that the crosshatch patterns consist of slip steps produced by misfit dislocations at the Si@sub 0.77@Ge@sub 0.23@/Si(001) interface. The presence of oxide cap layers during annealing changes the mechanism of strain relaxation from strain-induced to misfit dislocation induced roughening and inhibits surface diffusion such that the evolution of crosshatch ridges from slip steps is limited. As a result, with oxide capped 240-nm-thick films, we obtain smooth, relaxed Si@sub 0.77@Ge@sub 0.23@ layers with w = 0.68 nm and R = 68% without the necessity of using several-µm-thick compositionally-graded buffer layers.