AVS 50th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM4
Sn-mediated Ge/Ge(001) Growth by Low-temperature Molecular Beam Epitaxy: Effects on Surface Roughening and Epitaxial Thickness

Thursday, November 6, 2003, 9:20 am, Room 329

Session: Modeling & Fundamentals in Thin Film Deposition
Presenter: K.A. Bratland, University of Illinois
Authors: K.A. Bratland, University of Illinois
Y.L. Foo, University of Illinois
T. Spila, University of Illinois
P. Desjardins, École Polytechnique de Montréal, Canada
J.E. Greene, University of Illinois
Correspondent: Click to Email
Fully-strained single-crystal metastable Ge@sub 1-x@Sn@sub x@ layers were grown on Ge(001) in order to probe the role of dopant and dilute alloy concentrations (C@sub Sn@ = 1x10@super 18@ cm@super -3@ to 6 at%) on surface roughening pathways leading to epitaxial breakdown during low-temperature molecular beam epitaxy (LT-MBE) of compressively strained films. The growth temperature was chosen to be 155 °C due to limited epitaxial thicknesses at lower temperatures and significant Sn surface segregation at higher temperatures. The addition of Sn during Ge(001) LT-MBE was found to give rise to two competing effects. At very low concentrations (x < 0.02), the dominant effect is a Sn-induced enhancement in both the Ge adatom mobility and the rate of interlayer mass transport, thereby suppressing kinetic roughening and resulting in significant enhancements in the critical thickness h@sub 1@ for the onset of epitaxial breakdown. With x = 0.010, for example, the surface width w normalized to h@sub 1@, which is 2.6x10@super -3@ for pure Ge(001) layers, decreases to 1.5x10@super -3@ while h@sub 1@ increases from 7700 Å to 1.40 µm. Furthermore, layers which are fully epitaxial to thicknesses h > 1.9 µm are obtained with the incorporation of Sn in concentrations ranging from 1x10@super 18@ cm@super -3@ to 1.0 at%. However, for x @>=@ 0.02, strain-induced roughening overcomes the Sn-induced surface smoothening effects and gives rise to a rapid decrease in h@sub 1@, which ranges from 5700 Å with x = 0.029 to 2350 Å with x = 0.061.