Theory and observation of enhanced, high field hole transport in Si1-xGex quantum well p-MOSFET's

Kaushik Bhaumik, Yosi Shacham-Diamand, J. P. Noel, Joze Bevk, L. C. Feldman

Research output: Contribution to journalArticlepeer-review


We report on the observation of enhanced high field hole velocity in strained Si/Si1-xGex/Si quantum wells. This effect manifests itself in the drive current capability of nanometer scale p-channel Quantum Well Metal-Oxide-Semiconductor-Field-Effect-Transistors (p-QWMOSFET's). The high-field transport of a two-dimensional hole gas confined in a Si/Si1-xGex/Si quantum well is formulated and solved. The results indicate an increase in the hole saturated drift velocity in strained SiGe quantum wells with increasing Ge mole fractions up to x = 0.5. This is a consequence of the optical phonon spectrum of the strained SiGe alloy remaining Si-like (i.e., high energy) while the carrier transverse effective mass decreases with higher Ge content. To investigate the theoretical prediction of increased high-field drift velocity, p-QWMOSFET's were fabricated with Si/Si1-xGex/Si quantum well heterostructures grown by Molecular Beam Epitaxy (MBE) with varying Ge mole fractions, x. The fabrication sequence maintained a low thermal budget to prevent strain relaxation in the SiGe layer and involved a mixed optical/electron beam lithography scheme to define junction-isolated transistors with a minimum drawn gate lengths of 200 nm. The measured saturated transconductance, gmsat, of the p-QWMOSFET's were 20-50% higher than that of a reference Si p-MOSFET under equivalent biasing conditions. The importance of this gmsat increase for high-speed, low-power VLSI applications is discussed.

Original languageEnglish
Pages (from-to)1965-1971
Number of pages7
JournalIEEE Transactions on Electron Devices
Issue number11
StatePublished - Nov 1996
Externally publishedYes


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