Kazuaki Ohmi

A 2.4-GHz/5-GHz CMOS low noise amplifier with high-resistivity ELTRAN(R) SOI-Epi/sup TM/ wafers

The performance of radio frequency integrated circuits (RFICs) in silicon-on-insulator (SOI) technology can be improved by using a high-resistivity SOI substrate. We investigated the correlation between substrate resistivity and the performance of a low noise amplifier (LNA) on ELTRAN SOI-Epi wafers, whose resistivity can be controlled precisely. The use of high-resistivity ELTRAN wafers improves the Q-factor of spiral inductors, and increases the gain and narrows the bandwidth of the LNA.

An experimental observation of photo-induced carrier multiplication in hydrogenated amorphous silicon

A photo-induced carrier multiplication in a hydrogenated amorphous silicon has been observed. A careful measurement of photo-carrier generation has been done with amorphous silicon Schottky barrier structure junctions as a function of incident photon energy in the range between 1.55eV and 6.2eV. The quantum efficiency is estimated to be multiplied by a factor of two in higher photon energy region than 5.4eV. This multiplication can be explained by an interband carrier ionization due to the energy given by a high energy photo-carrier.

Amorphous Avalanche Photodiode with Large Conduction Band Edge Discontinuity

An amorphous avalanche photodiode (APD) with a heterojunction of hydrogenated amorphous silicon carbide (a-SiC:H) and hydrogenated amorphous silicon germanium (a-SiGe:H) was formed. The band gaps of a-SiC:H and a-SiGe:H are 3.5 eV and 1.55 eV, respectively. The discontinuity of conduction bands at the heterojunction is larger than the band gap of a-SiGe:H. In this amorphous APD, photocurrent multiplication is observed under low electric field. The quantum efficiency starts to exceed unity when the conduction band discontinuity becomes larger than the band gap of a lower-gap material, and it is likely to saturate at 2. The slope of photoelectric conversion characteristics is 1.00. The multiplication is explained by the impact ionization process at the band edge discontinuity region.