Toshihiko Hamasaki

Low‐temperature crystallization of doped a‐Si:H alloys

Crystallization of phosphorus‐doped a‐Si:H has been initiated at a substrate temperature below 200 °C, under the deposition conditions of a low flow rate of silane and in the presence of an external magnetic field. Along with the crystallization, the doping efficiency of the resulting Si:H films has been remarkably improved. Room‐temperature conductivity as high as 27 Ω−1 cm−1 has been achieved at a doping ratio of NPH3/NSiH4=5.6×10−3 for a specimen deposited at 30 C. Optical emission spectroscopy during the plasma deposition has revealed that a weak emission intensity of the SiH band with respect to hydrogen lines and the absence of emission from the doubly excited states of hydrogen molecules are necessary conditions for the crystallization of doped Si:H films.

High‐rate deposition of amorphous hydrogenated silicon from a SiH4 plasma

An extremely high deposition rate of amorphous hydrogenated silicon has been achieved by employing a new rf discharge technique. The deposition rate has been increased to more than 50 A/s at a substrate temperature of 200u2009°C without accompanying any appreciable deterioration in the electronic and structural properties as compared to those of specimens prepared at a conventional deposition rate (∼1 A/s). Thermal stability of the high‐rate samples is improved with respect to that of low‐rate specimens.

Novel effects of magnetic field on the silane glow discharge

We have measured the optical‐emission spectra of the silane plasma as a function of the external magnetic field, together with the growth rate and vibrational spectra of the resulting a‐Si:H films. The optical‐emission intensities of the reactive species SiH, H2, and H produced in the plasma are appreciably affected by the magnetic field, and the corresponding change in the hydrogen bonding of the deposited films is interpreted in terms of chemical reaction among the species.

Two-Phase Structure of a-Si1-xNx:H Fabricated by Microwave Glow-Discharge Technique

Amorphous Si1-xNx:H films (x lesssim0.1) were made by the microwave discharge technique. At x less than 0.05, both the activation energy Ea of the conductivity σ and the optical energy bandgap Eop of a-Si1-xNx:H films were almost constant, while σ decreased rapidly with increasing x. It is predicted from the intensity variation of the Si-H stretching modes as a function of x that the film consists of mixed phases of a-Si and a-Si3N4, and that Eop and Ea are determined by the a-Si phase.

Nucleation of Microcrystallites in Phosphorus-Doped Si:H Films

Structural properties of partially crystallized Si:H films prepared by glow discharge technique have been studied by Raman scattering and optical absorption spectra. The structure of the Si:H films is found to be a mixture of microcrystalline and amorphous phases. The volume fraction of a microcrystalline part in the Si:H network was determined to be 0.37–0.58 on the basis of the effective-medium theory.

Preferential segregation of dopants in μc-Si:H

Abstract Electronic and structural properties of heavily B-doped μc-Si:H films prepared by rf glow discharge technique have been studied by Raman scattering, IR absorption, SIMS and conductivity measurements. It is found that boron atoms in μc-Si:H tend to segregate in the amorphous tissue. The remarkable difference in doping efficiency between B- and P-doped μc-Si:H was interpreted in terms of the different degree of dopant segregation in the amorphous phase.

New mode of plasma deposition in a capacitively coupled reactor

A new technique of radio frequency plasma‐enhanced chemical vapor deposition is developed to achieve extremely high growth rates exceeding 40 A/s. The two disk electrodes are surrounded by a stainless‐steel mesh at ground potential, and an external variable reactance is connected between the substrate electrode and the ground. When the resonance condition in the circuit composed of the variable reactance and the substrate sheath capacitance is satisfied, a very high deposition rate is obtained as a result of dramatic change in the potential distribution between the two electrodes.

A New Technique of Boron Doping in Si: H Films

Very high doping efficiency of boron atoms in hydrogenated silicon has been achieved using the glow discharge of a SiH4-B2H6 mixture gas under conditions of a low concentration of SiH4 and application of magnetic field to the plasma column. A maximum conductivity of 7.8 Ω-1cm-1 has been obtained at a doping ratio of NB2H6 /NSiH4 =2.6%. This high conductivity is found to be related to partial crystallization of amorphous Si:H network.

Growth kinetics of amorphous hydrogenated silicon studied by pulsed rf discharge

Abstract The growth rate and hydrogen bonding configuration of a-Si:H prepared by a pulsed rf discharge technique were measured as a function of repetition frequency. The result was compared with the case of the gas-phase polymerization of monomers C 2 H 2 , C 2 H 4 , and C 2 H 6 in a pulsed rf discharge. From distinct difference between the pulsed-plasma depositions of a-Si:H and C:H films, it is concluded that the growth of a-Si:H proceeds through the heterogeneous reactions among chemical species on the substrate surface.

Effect of Annealing on Hydrogenated Amorphous Silicon Prepared at High Deposition Rate

Structural and electronic stabilities in hydrogenated amorphous silicon (a-Si:H) prepared at deposition rates ranging 10–50 A/sec have systematically been investigated by observing annealing effects on the spectra of optical absorption, photoluminescence and infrared absorption. High-rate samples deposited at a substrate temperature of 200°C exhibited excellent thermal stability in electronic properties at annealing temperatures up to 465°C.