Hybrid surface roughening modes during low-temperature heteroepitaxy: Growth of fully-strained metastable Ge1-xSnx alloys on Ge(001)2x1

Fully-strained single-crystal metastable Ge1-xSnx alloys were grown on Ge(0 01) up to their critical epitaxial thickness values t(epi)(x) in order to p robe surface roughening pathways leading to heteroepitaxial breakdown durin g low-temperature molecular-beam epitaxy under large compressive strain. Al l films with x > 0.09 have comparable roughnesses while films with x < 0.09 are considerably tougher with larger lateral feature sizes. Roughening rat es increase with increasing x for films with x > 0.09,due to a new hybrid r elaxation path which only becomes accessible under high strain as kinetic r oughening provides surface oscillations on lateral length scales that allow bulk relaxation through strain-induced islanding at growth temperatures wh ere it could not otherwise proceed. [S0163-1829(99)01247-3].