Parasitic Channels in SiGe Heterojunction p-Metal Oxide Semiconductor Field Effect Transistors

Heterojunction p-metal oxide semiconductor field effect transistors (p-MOSFETs) with -buffer heterostructure (SiGe p-MOSFETs) were fabricated and their parasitic channels induced at the (gate)/Si-cap interface were investigated. The dependence of the parasitic channel on the substrate doping concentration demonstrated that the parasitic channel caused more degradation in the transconductance of the SiGe p-MOSFETs at higher substrate doping concentrations. Si-cap thickness dependence of the transconductance was also examined. As the Si-cap thickness is decreased, the influence of the parasitic channel on the transconductance is strongly reduced. Furthermore, the reduction of the Si-cap thickness makes the parasitic channel less sensitive to the substrate doping concentration, the gate oxide thickness, and the gate voltage. At a Si-cap thickness of less than 2 nm, the SiGe p-MOSFETs can maintain their advantage over Si p-MOSFETs even in the future for smaller sizes. © 2002 The Electrochemical Society. All rights reserved.