Koichiro Yuki

Fabrication of Novel Si Double-Barrier Structures and Their Characteristics

A novel Si (silicon)-based double-barrier structure (DBS) is newly proposed to study Si resonant tunneling devices. To form a thin Si single-crystal plate as a quantum well, anisotropic wet chemical etching and thermal oxidation are adopted. The DBS has a 43 nm-wide Si quantum well and 2.3 nm-thick SiO 2 barriers. The electrical characteristic exhibits negative differential conductance (NDC)

Bandgap and Strain Engineering in SiGeC Heterojunction Bipolar Transistors

The incorporation of C into Si1-xGex alloys contributes to enlarging the critical layer thickness and to improving the thermal budget. It also realizes a narrower bandgap with compensated strain. These effects would introduce good performance at high frequency in the devices. We fabricate heterojunction bipolar transistors (HBTs) with an Si1-x-yGexCy base layer using ultrahigh-vacuum chemical vapor deposition (UHV-CVD) technology. The bandgaps of Si1-x-yGexCy base layers are measured by the evaluation of the collector current dependence on temperature. The strain of the pseudomorphic Si1-x-yGexCy layer is also extracted by an analysis of the X-ray diffraction spectra. Good flexibility of Si1-x-yGexCy alloy is shown for the bandgap and strain engineering. The devices using the excellent characteristics of Si1-x-yGexCy alloy have numerous applications for wireless telecommunications.

Reduction of neutral base recombination in narrow band-gap SiGeC base heterojunction bipolar transistors

Narrow band-gap SiGeC base HBTs were fabricated by Si compatible processing. By introducing 0.3% carbon into the SiGe layers, lattice strain was decreased and neutral base recombination localized at the collector-base heterojunction was significantly reduced.

Fabrication and Transport Properties of Gate-All-Around Silicon Quantum Wire Transistor

A novel fabrication method of silicon quantum wire Gate-All-Around Iransistor (GAAT), in which the gate oxide and the gate electrode are wrapped around the ultra fine silicon quantum wire, has been proposed. In order to verify one-dimensional (1D) subbands effects, we have studied quantum transport in Si quantum wire GAAT with a width of 50nm at low temperatures in zero-magnetic field and in fields up to 10T. Electrical population of lD subbands and magnetic depopulation of lD subbands are clearly observed.

Base Current Control in Low-VBE-Operated SiGeC Heterojunction Bipolar Transistors Using SiGe-Cap Structure and High-Carbon-Content Base

We have demonstrated the low-VBE operation of SiGeC heterojunction bipolar transistors by introducing a novel device design concept using the SiGe cap structure and high Ge- (up to 25%) and C- (up to 0.8%) content base. We successfully controlled the base current by designing the SiGe cap structure and C content, which enabled us to obtain suitable values of hFE and BVCEO, while maintaining a high collector current and high-frequency performance. We clarified that the recombination around the emitter-base junction is enhanced by introducing the SiGe cap structure and high C content, which contribute to the increase of the base current.