K. H. Oh

Charge trapping on different cuts of a single‐crystalline α‐SiO2

A scanning electron microscope is employed for the investigation of charging on different cuts of an α‐SiO2. A method for the determination of trapped charges is proposed. Charging on different cuts is observed to decrease in the order of z cut, 30° cut, 45° cut, and 60° cut of the α‐SiO2. This phenomenon is related to permittivity, defect density, and stress of the samples. Details of the experiments and the method of charge determination are given.

Variation of trapping/detrapping properties as a function of the insulator size

Using the scanning electron microscope we have investigated the physical parameters determining the size effect of various dielectric samples submitted to a surface electric field. It is shown that the size effect is a function of the static permittivity and of the space charge distribution. The results are explained by the consideration of charge diffusion and polarization relaxation processes resulting from the space charge formation. A one‐dimensional mathematical model has also been used to describe space charge distribution. The findings were consistent with the experimental observations.

Dielectric polarization relaxation measurement in α‐SiO2 by means of a scanning electron microscope technique

A scanning electron microscope is used as a tool to study dielectric relaxation processes in α‐SiO2 by measuring the leakage current in the sample surrounded by a metallic aperture. A transient time (t t ) of the order of a few seconds appears before the steady‐state current is established. The time dependence of the trapping rate is found to follow a power law and to be related to relaxation processes of a dielectric under electrical and thermal stress.

Variation of the relative permittivity of charged dielectrics

The variation of the relative permittivity of charged dielectrics with trapped charge density has been investigated by a time-resolved current method, in conjunction with a mirror image method employing a scanning electron microscope. The calculation is made by a mathematical expression derived from classical electromagnetic theory. It is found that the relative permittivity of the charged area in the polymethylmethacrylate sample increases with the trapped charge density and saturates at a certain value of the trapped charge density. These observations have been discussed by analogy with the dielectric saturation occurring at a high applied external electric field.

A Monte Carlo model for trapped charge distribution in electron-irradiated α-quartz

The space dependence of charge carriers trapped in α‐quartz under electron‐beam bombardment is investigated using a Monte Carlo algorithm. The average energy of the electron after being detrapped from a trap site is first calculated by considering both the polar and nonpolar phonon scatterings. Later, the detrapping and trapping rates are also included in the model to obtain a stable trapped charge distribution, which is found to be dependent on the size as well as the temperature of the sample. Comparisons with experimental results of the size effect on the dielectric strength obtained from a scanning electron microscope are also made.

Monte Carlo simulation of size effect on the dielectric strength of /spl alpha/-quartz

The size effect (SF) in a dielectric subjected to a surface space charge field has been defined as the slope of the curve ln(V/sub s//r) vs ln(r), where V/sub s/ and /spl Gamma/ are the critical surface potential and length of the sample, respectively. SF is an important material parameter affecting the breakdown voltage, the space charge detrapping field, the friction coefficient, the wear and the fracture toughness of the dielectric. In the present work, the SF effect was investigated. The experimental study was carried out in an SEM (scanning electron microscope) using an electron beam to bombard the dielectric. The space charge distributions for different sizes are obtained separately from macroscopic equations and microscopic simulation.<<ETX>>

A thermal control unit for microwave measurements of conductivity of a semiconducting material

A simple thermal control unit, together with a transmission microwave bridge have been constructed for the measurement of electrical conductivity at the X-band frequency of a silicon sample in the range 323 to 573 K. The temperature dependence of the conductivity and hence the band gap of Si were obtained. The technique may be used for other semiconducting materials.

A simple microwave method of moisture content determination in soil samples

A simple empirical equation for the measurement of the moisture content in a soil sample by using a microwave bridge to measure attenuation and phase shift through the sample is proposed. A calibration chart has been obtained from this equation for the convenient determination of the moisture content in a soil sample of unknown density. The validity and applicability of the equation has been confirmed by measurements on several soil samples of varying densities and thicknesses.

Field dependence of the overshoot phenomena in InP

Abstract The Ensemble Monte Carlo method has been used to investigate the velocity overshoot effect in InP, for applied fields greater than 10 kV cm -1 . We confirmed that the effect that occurs in InP is caused by the rapid transfer of charge carriers from a high mobility Γ -valley to a low mobility L-valley. Detailed comparison with the results obtained for GaAs by Xing Zhen [Ensemble Monte Carlo modeling of high-field transport and ultra-fast phenomena in compound semiconductors, Thesis (1990)] has also been made and commented on

The investigation of charging on /spl alpha/-quartz facets by a SEM technique

Electrons trapped on different cuts of /spl alpha/-quartz are determined. From an SEM (scanning electron microscope) mirror image for the charge potential. Different charging abilities for the various cuts are observed; charging ability decreases with increase of cutting angle. This phenomenon is related to polarization energy, defect density, and stresses.<<ETX>>