A GATE-QUALITY DIELECTRIC SYSTEM FOR SIGE METAL-OXIDE-SEMICONDUCTOR DEVICES

The use of Si(1-x)Ge(x) alloys for p-channel high-transconductance MOSFET's requires a high-quality dielectric system. Direct oxidation of Si(1-x)Ge(x) alloys or even low-temperature deposition of SiO2 directly on Si(1-x)Ge(x) results in a very high interface state density. We show that the use of a thin (6-8 nm) Si cap layer grown epitaxially on the Si(1-x)Ge(x) layer with the subsequent plasma-enhanced chemical vapor deposition of silicon dioxide gives low (below 10(11) eV-1.cm-2) interface state density. The Si cap layer leads to a sequential turn-on of the Si(1-x)Ge(x) channel and the Si cap channel, as clearly observed in the low-temperature CV curves. We show that this dual-channel structure can be designed to suppress the parasitic Si cap channel. The MOS capacitors are also used to extract valence-band offsets.