Leakage currents in Si1-xGex virtual substrates:: measurements and device implications

Leakage currents originating in the Si1-xGex virtual substrates which are required in many Si heterostructure systems have been measured. Both ohmic (AuSb) and Schottky (Pt) contacts to a modulation-doped Si:SiGe heterostructure show significant leakage when the contacts cover deep pits originating from growth defects and contaminants. Shallower pits emerging later in the growth process do not contribute to extra conduction. These pits appear after growth of the graded Si1-xGex layer which leads us to conclude that carrier transport from the contact along the dense network of dislocations formed in the graded buffer layer is responsible for the leakage found in Si:SiGe systems making use of virtual substrates.