UC Berkeley

Over 40 years of scaling dimensions for new and continuing product cycles has introduced new challenges for transistor design. As the end of the technology roadmap for semiconductors approaches, new device structures are being investigated as possible replacements for traditional metal-oxide-semiconductor field effect transistors (MOSFETs). Band-to-band tunneling (BTBT) in semiconductors, often viewed as an adverse effect of short channel lengths in MOSFETs, has been discussed as a promising current injection mechanism to allow for reduced operating voltage for beyond MOSFET technology.

This dissertation discusses the proposal of BTBT for tunneling feld effect transistors (TFETs). Some early work is briefly reviewed to better appreciate the academic research landscape regarding BTBT. Then, experimental observations of a steeply switching enhanced-Schottky-barrier MOSFET are analysed in detail and the steep characteristic is plausibly explained by metal impurity trap states near the source tunneling junction. Next, follow-up experiments to investigate the role of traps in BTBT are reviewed with a likely explanation that traps in close proximity to the tunneling junction can lower the activation energy for BTBT. Finally, a source design study for a planar homojunction germanium-on-insulator TFET finds that a static reverse bias can dramatically alter the optimal doping profile for the source tunneling junction and highlights the importance of tight electrostatic control for improved I_ON/I_OFF in TFETs.