Superlattices and Microstructures 44 (2008) 79–85 www.elsevier.com/locate/superlattices Effect of the Ge mole fraction on the formation of a conduction path in cylindrical strained-silicon-on-SiGe MOSFETs Tarun Vir Singh, M. Jagadesh Kumar ∗ Department of Electrical Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi – 110 016, India Received 18 December 2007; received in revised form 11 February 2008; accepted 13 February 2008 Available online 19 March 2008 Abstract Using two-dimensional simulation, we have demonstrated the effect of the strain or Ge mole fraction x in a Si 1−x Ge x pillar on the conduction path in cylindrical strained-silicon (s-Si) MOSFETs. We show that for low values of the Ge mole fraction x in a Si 1−x Ge x pillar, the conduction path forms in the middle of the cylindrical SiGe pillar and not in the s-Si layer at the surface. Only for large values of the Ge mole fraction x in Si 1−x Ge x pillar does the current conduction path form in the s-Si layer, enabling the advantage of the mobility enhancement of carriers in the device operation. On the basis of our simulation study, we provide the minimum amount of strain or Ge mole fraction x in a Si 1−x Ge x pillar necessary in a device for the current to flow through the s-Si layer. c  2008 Elsevier Ltd. All rights reserved. Keywords: Strained silicon; SiGe; MOSFET; Threshold voltage; Mobility; Two-dimensional simulation 1. Introduction Scaling down of devices is one of the key methods of enhancing the transistor switching speed. But device length scaling beyond 100 nm has been seriously impeded by the increasing short channel effects (SCEs). Several structures have been proposed for overcoming SCEs, with double-gate (DG) and cylindrical surround gate MOSFETs being the most promising concepts [1–4]. For equivalent silicon and gate oxide thickness, cylindrical MOSFETs can be scaled to 35% shorter channel lengths than DG-MOSFETs for the same SCEs [5]. Cylindrical ∗ Corresponding author. Tel.: +91 11 2659 1085; fax: +91 11 2658 1264. E-mail address: mamidala@ieee.org (M. Jagadesh Kumar). 0749-6036/$ - see front matter c  2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.spmi.2008.02.007