| As silicon CMOS technology advances into the sub-20mn regime, fundamental and manufacturing limits impede the traditional scaling of transistors. Innovations in materials and device structures will be needed for continued transistor miniaturization and commensurate performance improvements. In this thesis, we introduce novel, strained germanium, heterostructure, Double Gate (DG) MOSFETs, which can significantly reduce the off-state leakage currents, while retaining their high current drivability and excellent electrostatic control.; In the first part, we look at the various challenges encountered in improving the performance of nanoscale MOSFETs. We discuss some of the current approaches to engineering the device structure and the channel material to enhance the overall device performance. We then present the electrical properties of Si(1-x)Gex alloys, going from Si(x=0) all the way to Ge(x=1), and the effect of strain on their bandstructure, carrier effective mass and mobility. We also discuss the material properties, growth technologies and state-of-the-art experimental research results on high mobility p-MOSFETs utilizing strained-SiGe layers.; Large Band-To-Band Tunneling (BTBT) leakage currents can ultimately limit the scalability of high mobility (small bandgap) materials. Through 1-D Poisson-Schrodinger, full-band Monte-Carlo and detailed BTBT simulations, we thoroughly analyze the tradeoffs between carrier transport, electrostatics and BTBT leakage in high mobility, sub-20nm, strained-SiGe (high germanium concentration), heterostructure, PMOS DG FETs. Our results show a dramatic (>100X) reduction in BTBT and excellent electrostatic control of the channel, while maintaining very high drive currents and switching frequencies, in these nano-scale transistors.; For the first time, through detailed experiments, we examine the transport and leakage in ultra-thin, strained-Ge MOSFETs on bulk and SOI. The fabricated devices show very high mobility enhancements of >4X (over bulk Si devices), while simultaneously achieving a low off-state leakage.; Finally, the tradeoffs between drive current, intrinsic delay, BTBT leakage and short channel effects have been systematically compared in futuristic high mobility channel materials, like strained-Si (0-100%), strained-SiGe (0-100%) and Ge. All possible combinations of strained Si(1-x)Ge(x) alloys grown on relaxed Si(1-y)Ge(y) virtual substrates have been evaluated. A detailed discussion on the optimal channel materials and device structures for future nanoscale p-MOSFETs is presented. |
