Mitsuru Kikuchi

Hall Effect in Bulk-Doped Organic Single Crystals

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N, cm-3 ) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk-doped organic single crystals. Here, the Hall effect in bulk-doped single-crystal organic semiconductors is measured. A key feature of this work is the ultraslow co-deposition technique, which reaches as low as 10-9 nm s-1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N, cm-3 ) and the Hall mobility (μH ) of bulk-doped rubrene single crystals, which have a band-like nature, are systematically observed. It is found that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.

Parts-per-Million-Level Doping Effects in Organic Semiconductor Films and Organic Single Crystals

Controlling the pn-type behavior of a semiconductor such as silicon by adding an extremely small quantity of an impurity (doping) is a central part of inorganic semiconductor electronics since the 20th century. Recent progress in the doping of organic semiconductors strongly suggests the advent of a new era of doped organic semiconductors. Here, the principles and effects of doping at the level of parts per million (ppm) in organic semiconductor films and single crystals are described, including descriptions of complete pn-control, doping sensitization, ppm doping using an extremely low-speed deposition technique reaching 10-9 nm s-1 , and emerging ppm-level doping effects, such as trap filling, majority carriers, homojunction formation, and decreased mobility, as well as ppm-level doping effects in organic single crystals measured by the Hall effect, which shows a doping efficiency of 24%. The Wannier excitonic doping of organic single crystals possessing band conduction and the defect science of organic single crystals related to carrier trapping and scattering are introduced as a new scientific field. The dawn of organic single-crystal electronics is also discussed.

Enhancing the photocurrent in high-photovoltage organic solar cells by doping

We obtained a 50% improvement in photocurrent with a photovoltage of 1.0 V by impurity doping organic photoactive codeposited films consisting of fullerene and a novel organic semiconductor. A reduced cell resistance and the formation of band bending were revealed to be the main reasons for the doping-induced improvement in photocurrent. A conversion efficiency of 3.8% was observed.

Modelling of noble gas-SiH4 gas mixture glow discharge positive column plasmas

Numerical modelling of He-SiH 4 , Ne-SiH 4 and Ar-SiH 4 gas mixture glow discharge positive column plasmas is conducted for the gas pressure from 0.1 to 30 Torr, the percentage silane gas mixture in a noble gas from 0.01 to 10%, and the electron density from 10 9 to 10 13 cm -3 . The results show that the plasma parameters significantly depend on the combination of the choice of the noble gas and the silane mixture fraction