Sn-enhanced epitaxial thickness during low-temperature Ge(001) molecular-beam epitaxy

The incorporation of dilute Sn concentrations C-Sn during Ge(001) low-temperature molecular-beam epitaxy significantly increases the critical thickness h(1)(T-s) for the onset of epitaxial breakdown. With C-Sn=6x10(19) cm(-3), h(1) increases by an order of magnitude at T-s=95 degreesC, while gains in h(1)(T-s) by factors ranging from 3.2 at 95 degreesC to 2.0 at 135 degreesC are obtained with C-Sn=1x10(18) cm(-3) (20 parts per million!). Nevertheless, the ratio of the surface width at breakdown to the in-plane correlation length remains constant, independent of T-s and C-Sn, showing that epitaxial breakdown for both Ge(001) and Sn-doped Ge(001) is directly related to surface roughening. We attribute the dramatic Sn-induced increases in h(1)(T-s) to enhancements in both the Ge surface diffusivity and the probability of interlayer mass transport. This, in turn, results in more efficient filling of interisland trenches, and thus delays epitaxial breakdown during low-temperature growth. (C) 2003 American Institute of Physics.