Strain modification in thin Si1-x-yGexCy alloys on (100) Si for formation of high density and uniformly sized quantum dots

The effects of alloying C with Ge and Si and varying the C/Ge ratio during the growth of very thin layers of the ternary alloy SiGeC grown on Si (100) substrates and the resulting strain modification on self-assembled and sel f-organized quantum dots are examined. During coherent islanded growth, whe re dislocations are not formed yet to relieve the strain, higher strain ene rgy produced by greater lattice mismatch acts to reduce the island size, in crease the density of islands, and significantly narrow the distribution of island sizes to nearly uniformly sized quantum dots. Strain energy can als o control the critical thickness for dislocation generation within the thre e-dimensional islands, which then limits the maximum height which coherent islands can achieve. After the islands relax by misfit dislocations, the is land sizes increase and the island size distribution becomes broader with t he increase of misfit and strain. The optimal growth for a high density of uniform coherent islands occurred for the Si0.49Ge0.48C0.03 alloy compositi on grown on (100) Si, at a growth temperature of 600 degrees C, with an ave rage thickness of 5 nm, resulting in a narrow size distribution (about 42 n m diameter) and high density (about 2 X 10(10) dots/cm(2)) of quantum dots. (C) 1999 American Institute of Physics. [S0021-8979(99)00801-4].