Yuichi Masaki

Kinetics of solid phase interaction between Al and a‐Si:H

The kinetics of solid phase interaction between Al and a‐Si:H have been investigated. The experiment led to the observation of low‐temperature crystallization as has been reported. The crystallization temperature was found to be 300–350 °C from diffraction studies. From the x‐ray photoelectron spectroscopy study, electron transfer from Al to Si was observed in the intermixing layer in samples annealed at RT and 200 °C whereas there is no evidence of the electron transfer for 300 and 350 °C annealed samples. To explain these results, a comparison is made with the interaction in the Cr/a‐Si:H system previously reported and the interdiffusion model is proposed.

Interaction in the Cr/amorphous‐silicon system

The kinetics of a low‐temperature silicide formation have been investigated in experiments on the solid‐phase interaction between Cr and amorphous Si (a‐Si). For the Cr/plasma‐enhanced chemical‐vapor‐deposited a‐Si:H system, it was found that amorphous interlayer was formed at the interface at RT. The compositional ratio of Cr to Si in the amorphous interlayer formed at RT was found to be about 5%. On the other hand, for the Cr/sputtered a‐Si system at RT, an interfacial amorphous layer with negligible thickness seemed to exist. From the experimental results and from the results previously reported, the kinetics of the low‐temperature interaction were discussed and a new model of an internal‐field‐assisted interaction was proposed.

Transient phases of a‐Si by rapid heating

A structural model of a‐Si and a model for its transient phases have been proposed. In these models, it is assumed that a‐Si is composed of many small regions (or clusters with a radius of about 50 A) having different free energies. When a‐Si is rapidly heated to a temperature slightly less than 1450 K so as to avoid crystallization, it transforms to a new phase in which both a‐Si clusters and super‐cooled l‐Si coexist. By using these models, anomalous phenomena observed in explosive crystallization and enhanced diffusion phenomena in rapid thermal annealing (RTA) process can be explained. Furthermore, the viscosity of super‐cooled Si fluid at 1000 °C induced by the RTA process is estimated to be 107–108 mPa s, which leads to the determination of T0 value of about 1300 K in Vogel–Fulcher–Tammann (VFT) relation. However, this T0 value differs from that previously reported. This discrepancy has been discussed and it is concluded that T0 in the VFT relation is not a constant but a function of (dT/dt).

Effects of gas flame annealing on the structure of poly‐Si films

The effect of gas flame annealing on the structure of polycrystalline Si films was studied using transmission electron microscopy and electron spin resonance. This annealing technique involved heating the sample surface to more than 1100 °C using flat gas flames with a scan rate of 1 mm/s and a heating rate of about 260 °C/min. Electron microscopy images revealed that the secondary grain growth proceeded with increasing the number of annealing times (annealing frequency) and that the grain size for samples annealed at 1360 °C was more than 1 μm whereas secondary grain growth was not significant for samples annealed at 1150 °C. Further, it was found that the spin density in the samples annealed at 1360 °C decreased from 1.5×1018 cm−3 to 3.8×1017 cm−3. It was concluded from the spin resonance results and the electron microscopy images that the secondary grain growth consists of two processes, the initial structural rearrangement of the grain boundaries and the subsequent grain growth.

Heating rate dependence of phase transition temperature in Se7Te3 glasses

The crystallization and the glass-transition temperatures, T c and T g , of Se 7 Te 3 glasses were measured at heating rates of 10 -2 to 10 2 °C/min. T c and T g exhibit weak heating-rate dependences at low heating rates, but the slopes of their heating-rate dependences become steep with increasing heating rate. T c and T g as a function of the heating rate are interpreted in terms of nucleation and fragmentation processes in random networks.

Effects of high temperature rapid thermal annealing using a flat gas flame on the electrical properties of phosphorus‐doped polycrystalline silicon films

The effects of high temperature rapid thermal annealing (HT‐RTA) using a flat gas flame on the electrical properties of phosphorus‐doped polycrystalline silicon (poly‐Si) films in association with their microscopic structure were studied. Samples with a phosphorus concentration of 3.1×1017–6.0×1020 cm−3 were prepared and annealed by HT‐RTA ranging from 1150 to 1350 °C. During HT‐RTA, the sample surface was laterally swept by gas flames. The resistivity of the samples decreased with increasing annealing temperature, and the lowest resistivity was 4.8×10−4 Ω cm for the sample doped with P of 6.0×1020 cm−3 when annealed at 1350 °C. Hall mobility, on the other hand, increased first and then decreased with increasing P concentration. The highest Hall mobility was 71.3 cm2/V s for the sample annealed at 1350 °C of which the P concentration was 3.5×1019 cm−3. The results suggest that the grain boundary potential barriers for carriers decreased with increasing doping concentration and annealing temperature, and t...

On the viscosity change in strong and fragile glasses

Abstract The viscous behaviour of strong and fragile glasses has been interpreted on the basis of the fragmentation model in which it is assumed that (1) a vitreous system consists of “pseudomolecules” and (2) the system is fragmented and the fragment size decreases with increasing temperature. The results of numerical calculations show that the size of fragments in viscous flow is constant for strong glasses whereas for fragile glasses it decreases as temperature is increased from T g to T m .

Phase transition in non-crystalline solids viewed from heating

The heating-rate dependence of crystallization temperature, Tc, and the glass transition temperature, Tg, is studied from the view points of nucleation and fragmentation processes in disordered structures. Tc and Tg are expected to increase monotonically with heating rate. Such behaviors of Tc and Tg are classified into four characteristic regions with respect to the heating rate. Results are summarized in the Transient Phase Diagram where Tc and Tg are given as a function of heating rate. The scaling rule in the Transient Phase Diagram is given.

Study of glass transition based on the fragmentation model

Glass transition phenomena for a fictive V{sub 2}-VI{sub 3} compound have been described on the basis of fragmentation model in which glass materials begin to fragmentize at a certain temperature and the fragment size becomes small with increasing temperature. By a numerical calculation, the heating rate dependence of glass transition temperature was clearly presented, and fragment sizes at glass transition and melting temperature were estimated at 1.4 {micro}m and 20{angstrom} respectively. Further, thermodynamic aspects were discussed using the model and it was concluded that the glass transition is a sort of the first order transition.