The objective of the proposed research is to investigate a new class of semiconductor devices compatible with dominant silicon technology -- tunneling transistors fabricated in epitaxial germanium-on-insulator channels. These devices are not constrained, in principle, by the subthreshold swing limit of standard field effect transistors, so there is the potential of obtaining large on/off current ratios at room temperature while reducing the power supply voltage and hence the power consumption of large integrated circuits. The enabling approach involves the use of ultrathin single-crystal germanium-on-insulator channels combined with lattice-matched epitaxial high- dielectrics, all grown on silicon substrates.
Intellectual merit: Although silicon-based tunneling transistors are a topic of current research in industry, germanium-on-insulator devices are both unexplored and promising, because the smaller Ge bandgap promises orders of magnitude higher tunneling current at the same power supply voltage and current drive is a key metric for downscaled transistors, tunneling or field-effect, that will determine how much device scaling will help in the future. Another interesting aspect of tunneling transistors is that they can dispense with the inversion channel altogether, greatly reducing the capacitance, which may prove of interest for high-speed analog amplifiers. Planar lateral tunneling transistors, with and without an inversion channel, fabricated in all-epitaxial Ge-on-insulator heterostructures will be studied by the combined IBM-Brown research team, which has complementary expertise and an existing close co-PI collaboration on Ge devices.
Broader Impact: The proposed research will gauge the technological potential of germanium-based tunneling transistors compared to standard field-effect devices. The insertion of alternative channel materials, such as Ge, is a key part of the silicon technology roadmap. The alternative tunneling devices to be studied maintain VLSI compatibility and room temperature operation, making them viable for hybrid electronic circuits. The proposed research will have an educational impact, with Brown graduate students interacting closely with IBM Research (including summer internships), and undergraduates gaining research experience, including undergraduates from minority institutions identified through the Brown MRSEC, which has a focused outreach program.
