Kazuo Morigaki

Screening and Stark Effects Due to Impurities on Excitons in CdS

Properties of intrinsic and bound excitons in CdS with Cl donor concentrations over a wide range are investigated by measuring emission and reflection spectra at liquid helium temperature. As a res...

Electron Spin Resonance Studies of Interacting Donor Clusters in Phosphorus-Doped Silicon

Electron spin resonance of donor electrons has been investigated in phosphorus-doped silicon at 46GHz and in the temperature range from 1.5 K to 4.2 K. From the temperature variation of the resonance line due to the donor clusters, that consist of more than several donor atoms, it is concluded that the exchange coupling between donor atoms within the cluster is antiferromagneric. The analysis of the peak shift of the central line indicates that there exists a weak ferromagnetic exchange coupling between the donor clusters. One of the striking result in our experiment is that two resonance lines separated by 0.8 Oe from each other at 1.5 K are observed at the donor concentration of 1.74×10 18 cm -3 which belongs to the intermediate concentration region, that is the transition region from the non-metallic to metallic type of impurity conduction. Both resonance lines are interpreted as being due to two types of the donor clusters which may correspond to the non-metallic and the metallic region in the crystal.

Effect of hydrogen dilution on the optical properties of hydrogenated amorphous silicon prepared by plasma deposition

Abstract A series of experimental studies has been made on the effect of the dilution of silane with hydrogen on optical properties of hydrogenated amorphous silicon films (a-Si:H) prepared by plasma deposition as functions of the gas-volume ratio γ (=[SiH4]/([SiH4] + [H2])) and the substrate temperature T s. The effect of hydrogen dilution has been discussed in terms of the obtained values of the deposition rate R d, the optical gap E g, the Urbach energy E u, the defect density N d, the hydrogen content C H and the refractive index n 0 and their correlations between them and the hydrogen-bonding configuration estimated from infrared absorption spectra. Its effect strongly depends on T s and decreases N d and E u from γ = 100% to about 20%. The effect for reducing them is discussed in terms of the surface-limited optimal growth model containing the hydrogen dilution effect. On decreasing γ from about 10%, both N d and E u increase in spite of the decrease in R d. This result is due to the onset of the fo...

Temperature dependence of electron spin resonance in fluorinated amorphous carbon films

Electron spin resonance (ESR) measurements were carried out at 9.2 GHz in the temperature range between 5 and 300 K on fluorinated amorphous carbon (a-C:F) films prepared by plasma chemical vapor deposition (CVD) with different fluorine concentrations and dangling bond densities. The observed temperature dependences of the line width are interpreted in terms of motional narrowing due to hopping motion of dangling bond electrons and also surrounding fluorine motion, taking into account that the original line broadening arises from hyperfine splitting due to surrounding fluorine nuclei. From the temperature dependences of the line width, we conclude that several types of dangling bond centers with different environments are present with different relative densities among a-C:F samples.

Resistivity Decrease Due to Donor Spin Resonance in n-Type Germanium

A decrease in the resistivity associated with donor spin resonance has been observed in the liquid helium temperature range in arsenic- and phosphorus-doped germanium, whose donor concentrations belong to the intermediate concentration region of impurity conduction phenomenon. The relative changes of the resistivity due to the donor spin resonance have been measured as a function of static electric field applied to samples, temperature, microwave power, and donor concentration. The experimental results are explained on the basis of the spin energy transfer model in which the existence of the two different electronic systems, that is, the donor spin system being responsible for the donor spin resonance and the mobile electron system contributing to the charge transport of the intermediate concentration region at low temperatures is assumed, and the microwave energy absorbed by the donor spin system is transferred to the mobile electron system through their mutual exchange interaction and it turns out to in...

Model of the light-induced creation of two types of dangling bonds in a-Si:H

We present a new model of the light-induced creation of two types of dangling bonds in a-Si:H. The numerical calculation on the rate equation based on the model accounts for differences in the presence of two types of dangling bonds between high-quality samples and low-quality samples and also the observed kinetics of light-induced dangling bond densities in a-Si:H.

Light-Induced Annealing of Dangling Bonds in a-Si:H

We have investigated the kinetics of light-induced defect (dangling bond) creation and annealing processes in a-Si:H containing a large amount of hydrogen at 300 K and 77 K using the ESR technique. We have obtained direct evidence for the light-induced annealing of dangling bonds at 300 K. A model, in which nonradiative recombination of electrons and holes at hydrogen-related dangling bonds is taken into account, is presented to interpret the experimental results.

Light-induced defect creation under pulsed subbandgap illumination in hydrogenated amorphous silicon

We have observed that pulsed subbandgap illumination creates dangling bonds with a density of about 10 18 cm m 3 in high-quality hydrogenated amorphous silicon films. Such a light-induced creation of dangling bonds can be accounted for in terms of a model in which self-trapping of holes in weak Si-Si bonds adjacent to a Si-H bond plays an important role. The kinetics of thermal annealing of the light-induced dangling bonds have been examined, in which half of the defects are annealed out at temperatures above 180C, but half of them remain.

Anisotropic magnetic centres in hydrogenated microcrystalline and polymorphous silicon

Abstract Anisotropic magnetic centres in hydrogenated microcrystalline and polymorphous silicon have been observed in electron spin resonance spectra. The nature of anisotropic magnetic centres is discussed in terms of dangling bonds with axially symmetric g -values through a diagram of δ g // vs. δ g ⊥ , i.e. the g -shifts parallel and perpendicular to the symmetric axis, respectively.

Light-induced defect creation under intense optical excitation in hydrogenated amorphous silicon

A model of light-induced creation of dangling bonds under intense illumination in hydrogenated amorphous silicon is presented. Numerical calculations on the density of light-induced dangling bonds are compared with the observed results obtained by Ogihara et al. under pulsed illumination for high-quality hydrogenated amorphous silicon. Good agreement between calculations and experiments is obtained for the density of light-induced dangling bonds and its dependence on illumination time.