Uichi Itoh

Vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8

The vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8 are reported for the wavelength region 107–220 nm using synchrotron radiation as a light source. Absorption maxima of these compounds were found at the exciting wavelengths of 115–119 nm. Broad peaks observed were mostly assigned as primarily Rydberg transitions of the σSiH and σSiSi bonding electrons to the 4s, 4p, and 4d orbitals. The absorption features of germane resemble those of monosilane. In the photoexcitation of monosilane, the emission of the SiH(A 2Δ→X 2Π) transition was observed and its onset was found to be 132±2nm. The absorption spectrum of disilane showed five peaks. They were mostly assigned as 2a1g→4s, 2a1g→np(n=4−6) transitions and the strongest band was overlapped by 1eg→4d and 1eu→4p Rydberg transitions. In trisilane molecules three very weak and broad peaks were recognized and assigned as 3b2→4s, 4p and 4a1→4s, 4d Rydberg transitions. The strongest band was tentatively assigned as the superposition of...

Hydrogenated amorphous silicon prepared by ArF and F2 excimer laser‐induced photochemical vapor deposition

Hydrogenated amorphous silicon (a‐Si:H) films were prepared by laser‐induced photochemical vapor deposition using ArF and F2 excimer lasers. Disilane (Si2H6) and trisilane (Si3H8) diluted with helium were used as the reaction gases for the ArF laser and monosilane (SiH4), disilane, and trisilane for the F2 laser. A good linear correlation was found between the estimate of deposition rate derived from gas phase photoabsorption and the observed deposition rate, indicating that one‐photon process governs the film deposition rate. Density of excited molecules in the gas phase was found to be an important factor in controlling the film properties. Laser irradiation onto the growing surface also affects the film properties through a decrease in the hydrogen incorporated in the film.

Photochemical vapor deposition of hydrogenated amorphous silicon films from disilane and trisilane using a low pressure mercury lamp

The photolysis of disilane (Si2H6) and trisilane (Si3H8) under direct excitation by light from a low pressure mercury lamp was carried out to prepare hydrogenated amorphous silicon films (a‐Si:H). The electronic and optical properties of the films were investigated as functions of preparation conditions such as partial pressure and substrate temperature. The conductivity of the films prepared from Si3H8 at 300 °C was 10−10 S cm−1 in the dark and 10−5 S cm−1 under the illumination of a He‐Ne laser with a photon flux of 1015 cm−2 s−1. The high photoconductivity was attained when the silane gas was blown over the substrate from a slit‐type nozzle placed beside the substrate plate at a pressure of less than 20 Torr.

Absorption spectra of SiCl4, Si2Cl6, SiF3CH3 and GeF4 in the VUV region

Abstract In the range 110–200 nm the absorption features of Si2Cl6 closely resemble those of SiCl4 and the peaks observed are tentatively assigned to the Rydberg transitions of a Cl lone-pair electron. Two diffuse bands in the SiF3CH3 absorption are also assigned to Rydberg excitations. The spectrum of GeF4 shows a broad band considered to be a valence excitation of the outermost orbital. The emission of the SiCl2 (A1B1→X1A1) transition was found in the photoexcitation of Si2Cl6.

Enhaancement of Photoconduction by Detrapping in Anthracene Crystal

The photocurrent in the anthracene crystal remarkably increases when trapped carriers were charged. It is explained as the optical release of the carriers from a deep trap, that is, detrapping process. By use of the increase of the photocurrent due to the detrapping, the informations on the carrier trapping mechanism and on the energy-depth of the deep trap were obtained. The energy-depth of the deep trap in anthracene was about 3 eV. In order to know the behavior of the deep trap, this method is useful.

Ruby-Laser Induced Photoconduction in 9, 10-Dichloroanthracene and 9, 10-Dibromoanthracene

Photoconduction induced by Q -switched ruby laser has been studied in 9, 10-dichloroanthracene and 9, 10-dibromoanthracene single crystals. The dependence of induced charges on the laser intensity was measured in the region from 10 23 to 3×10 24 photons/cm 2 ·s. Both compounds show the third power dependence in the higher intensity region. In the low intensity region, however, they show linear dependence. The carrier generation showing the linear dependence was explained as the process involving triplet excitons produced by the S - T absorption.

The 3-CN-4-MU dye laser in ethanol containing various amounts of water, acid or alkali

Abstract Dye laser emission from 3-cyano-4-methylumbelliferone in alcoholic solutions containing various amounts of water, acid, or alkali was studied, and the best solvent compositions for the dye were determined. By nitrogen laser pumping, (1) anhydrous ethanolic solution gave very intense laser emission in 400–470 nm region. (2) Aqueous ethanol solutions containing more than 4% of water gave laser of longer-wavelength region, 440–510 nm. Among them, the solution of 16% in water content gave the highest powers. Addition of very small amount of perchloric acid solution to them resulted in a slight expansion of the tuning range toward the shorter wavelength without reducing the intensities. By flashlamp pumping, (3) only the laser of the longer-wavelength region was obtained with aqueous ethanol solutions. The optimum water content to give the highest power was 35–45%.

Electrical Conduction of Anthracene Crystal

Electrical conductivity and activation energy were measured in doped-anthracene crystals and a highly purified anthracene crystal in a temperature range from 370 K to 420 K. It was found that the conductivity was proportional to the concentration of impurity molecules. Main carrier generation process in the dark conduction was deduced to be an extrinsic bulk generation associated with impurity molecules. Other mechanisms such as intrinsic generation or carrier injection from electrodes were denied. The conductivity and the activation energy were respectively 1.63 eV and 1.4×10 -17 ohm -1 cm -1 at 400 K in the direction perpendicular to the ab-plane of the purified anthracene crystal. It has not been reported that the conductivity lower than the above value has ever been observed.

Ruby-laser induced photoconduction of α- and β-form crystals of 9, 10-dichloroanthracene

Abstract The carrier generation processes via the two-photon absorption and via the singlet—triplet absorption were investigated. The directions of the transition dipoles of both absorptions are discussed.

Various Detrapping Processes in Anthraquinone-Doped Anthracene Crystal

The photo-carrier generation process by optical detrapping effects has been observed in anthracene crystals provided with hole[1] and electron[2] injecting contacts. It has been reported that there were the direct release of trapped carriers from traps about 1 eV to conduction state and the indirect release due to the interaction of the trapped carriers and two types of excitons, that is, triplet and singlet excitons. On the other hand, it is expected that there are deeper traps than 1 eV in impurity-doped anthracene crystals. In fact, it was found that free carriers in electrical conduction were generated thermally from such deep traps in doped anthracene crystals.[3] In this note, various detrapping processes which include the direct release from the deeper traps than 1 eV are investigated in anthraquinone-doped anthracene crystal. Further, it is reported that the enhancement of the photocurrent by the optical detrapping effects is observed in the crystal provided with non-injecting contacts, when the traps have been charged with carriers before measurements.[4, 5]