Ken Idota

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.

Ultrahigh vacuum system for atomic-scale planarization of 6 inch Si(001) substrate

Abstract Ultrahigh vacuum (UHV) system equipped with aluminum radiation shields has been developed in order to obtain atomically flat Si(001) surfaces in a large area. Aluminum radiation shields were employed to suppress the temperature rise of chamber walls. The UHV system has enabled a 6 inch substrate to be heated up to 700°C under a pressure of less than 10 −8 Pa range. The surface structure of the substrate was confirmed by the reflection high energy electron diffraction (RHEED), when the 6 inch substrate was heated at 600°C in UHV after a modified RCA cleaning, the RHEED pattern indicated oxide free surface consisted of2 × 1structure. The roughness was evaluated from numerous observations by cross-sectional transmission electron microscopy (XTEM). Root-mean-square roughness of the Si surface was less than 0.1 nm for almost all over the 6 inch substrate. This implies that the heating in this system gives rise to the atomic-scale planarization of the 6 inch substrate.