Table of contents

For colour CMOS digital image sensors irradiated with different γ-ray doses, the average brightness and non-uniformity of the dark output images increase noticeably above 0.6 kGy. Some light regions appear on the images, their brightness and area becoming greater with increasing γ-ray dosage. The whole region becomes bright at 1.6–1.8 kGy. The light region has different positions at different doses, showing that the non-uniformity exists due to an unstable fabrication process. For sensors maintained at room temperature for 7 days after irradiation, the brightness and area of these regions increase, as well as the average brightness and non-uniformity. An explanation for the changes of the characteristic parameters is presented.

We have used the heat pulse technique to study phonon transport in 6H–silicon carbide. We have directly detected ballistic acoustic phonons which have propagated across the substrate and have observed the arrival of phonons multiply reflected from the surfaces, suggesting high crystal quality. From the heat pulse data, we deduce the velocities of the longitudinal and transverse acoustic modes. We have used phonon imaging techniques to obtain images of the phonon focusing in 6H–silicon carbide and have compared these with the results of theoretical calculations.

Modern electronic and optoelectronic devices are approaching nanometric dimensions where microscopic details cannot be treated in an effective way. Atomistic approaches become necessary for modelling structural, electronic and optical properties of such nanostructured devices. On the other hand, theoretical developments and numerical optimizations make device modelling approachable by atomistic methods. The purpose of this review is to report on microscopic theories to describe these nanostructured semiconductor devices. Empirical and density functional tight-binding as well as pseudopotential approaches are applied to the study of organic and inorganic semiconductor nanostructures and nanostructured devices. We show how these microscopic methods overcome the limitations imposed by the simplified approaches based on envelope function approximations and in the meantime keep the computational cost low. Typical calculations are shown for one-, two- and three-dimensional confined nanostructured devices, and comparisons with other approaches are outlined.

Au/CdTe Schottky devices were used to investigate various opto-electronic parameters such as open circuit voltage, short circuit current, fill factor, efficiency, spectral response, activation energy and the band gap of CdTe. The dependence of various device parameters on illumination and temperature has been investigated. The activation energy measurements revealed two trapping levels with energies 0.31 eV and 0.53 eV under 0.8 V bias. These levels showed voltage dependence and the zero-field values of the activation energy were estimated to be 0.49 eV and 0.66 eV, respectively. Devices with higher open circuit voltage showed an enhanced photo response in the long wavelength region. The dependence of the long wavelength cut-off on the open circuit voltage of the devices was explained as being due to the influence of the bulk collection function. The absolute zero value of the band gap was estimated to be 1.61 eV.

The high-bias behaviour of the dark forward and reverse current–voltage (I–V) characteristics of an undoped radio frequency (rf) magnetron sputter deposited boron carbide (p-B₅C)/p-type crystalline silicon heterojunction has been investigated at different ambient temperatures (130–300 K). The experimental forward current–voltage–temperature (I–V–T) characteristics indicate that the non-ohmic bulk conduction mechanisms operable in the highly resistive polycrystalline B₅C counterpart material of this heterojunction largely determine the behaviour of its forward current at high-bias voltages (>0.3 V). The hopping conduction model of Apsley and Hughes for a flat density of localized energy states (Apsley N and Hughes H P 1975 Phil. Mag.31 1327) can be utilized to elucidate the bias dependence of the measured heterojunction forward current over an extended bias-voltage range (0.4–2.7 V) at temperatures below 260 K. On the other hand, the junction-like conduction processes occurring in the depletion region should limit the high-bias behaviour of the measured heterojunction reverse current. Bardeen's model for a modified Schottky-like barrier at the p-B₅C/p⁺-Si interface can be satisfactorily applied to describe the reverse current–voltage characteristics at bias voltages larger than 0.4 V.

In this paper, we report on a systematic study of the formation of ohmic contacts to a GaTe layered crystal grown by the directional freezing method. In this study, the transmission line method (TLM) was used for the measurement of specific contact resistance of ohmic contacts to GaTe. We used In, Au, Al and Ag metals and Au–In eutectic alloy as contact elements. A ladder pattern was formed directly on the GaTe surface by evaporation of metals through a pre-patterned shadow mask. The lowest ohmic contact resistance, 2.5 ± 1.4 × 10⁻⁵ ohm cm², was achieved by annealing In at 200 °C for 2.5 min. Ohmic contacts fabricated by this process remained very stable up to six months after the anneal, although In contacts on some other samples, processed at 175–250 °C for 2.5–14 min, and having higher contact resistance, were unstable. The other elements used in this study showed rectification behaviour after annealing at 175–400 °C for 5 min. X-ray diffraction measurements showed that InGaTe₂ formation at the In/GaTe interface was minimized for the sample annealed with the optimum process. We found that the formation of InTe was essential for the successful production of ohmic contacts, and that the quality of the contacts was determined by the competition between InTe and InGaTe₂.

We investigate the transmittance of thin doped GaAs layers in the terahertz (THz) frequency range taking into account multiple reflections. Our experimental and theoretical study aims at providing a guideline for designing the top-side contact layers for THz emitters and receivers with direct, antenna-free coupling of the radiation. It is shown that the surface conductivity of the contact layer is the determining factor for the THz transmittance.

The influence of nitrogen incorporation on the reliability of ultrathin (<2 nm) rapid thermal oxides grown on strained Si/SiGe/Si heterolayers has been investigated. It is shown that rapid thermal oxidation using N₂O followed by N₂-annealing results in improved electrical properties and reliability in terms of stress induced leakage current, low bulk trap density, trap generation rate and high lifetime.

The physical system under study is a strained porous Si/Si/GeSi mesa stripe on a rigid Si substrate. We analyse the relaxation of elastic deformations in a pseudomorphic GeSi film using the finite element method. Calculations were carried out for stripes with a porosity of about 60% (the Young modulus is less than that of GeSi by a factor of ten). The widths of the stripe were 5 and 10 μm and larger, the heights were 1 and 5 μm. The calculations have proven that the relaxation is facilitated by the increase of the porous mesa height-to-width ratio (aspect ratio). However, the Si membrane (an ultra-thin Si film between the porous Si and GeSi films) decreases the value of elastic relaxation in the pseudomorphic layer. This effect is stronger for high aspect ratios. Contrary to the mesa stripe, an extensive porous Si layer cannot be a compliant substrate for the growth of a lattice-mismatched GeSi film. The residual elastic strains in GeSi films grown on porous mesa stripes appear to be much lower than those on non-porous mesas.

This study focuses on using synchrotron x-ray topography to study fully processed silicon wafer lots with varying, though, low average yields. The electrical circuits were fabricated in a mixed-signal complementary metal-oxide semiconductor (CMOS) process. Synchrotron x-ray section topographs are analysed with image processing software written entirely for this study. The software reduces image data by encoding the relevant factors into curve feature parameters, in order to quantify the strain gradients and defect factors present in the images. This information is then correlated against the integrated circuit process control monitoring (PCM) data and the yield, i.e. the electrical semiconductor process parametric values of the wafers. Several image features extracted from the synchrotron x-ray topographs show a strong correlation with certain PCM parameters, e.g. PMOS transistor threshold voltage, polysilicon sheet resistance and N⁻ contact chain sheet resistance, rather than with others, e.g. NMOS breakdown voltage. A positive correlation between good yield and strong near-surface strain gradient is found.

An investigation of the electrical properties of the SiON/n-Si interface is presented for applications in MOS and/or optical devices. The SiON films were deposited onto n-type Si substrates by CVD using different [O]/[N] ratios. Subsequent metallization led to the creation of metal-oxide-semiconductor (MOS) devices and electrical characterization took place in order to identify their electrical properties. Electrical measurements included current–voltage, capacitance–conductance–voltage (C–G–V) measurements and admittance spectroscopy, allowing the determination of the interface state density, the traps time constant and their distribution. Post-deposition annealing was also used and the annealed samples were subjected to the same investigation. The interface state density was found to lie between 1.74 × 10¹² eV⁻¹ cm² and 1.72 × 10¹¹ eV⁻¹ cm⁻² and the post-deposition annealing reduced these values.

In this paper, the effect of two-dimensional electron plasma formed on the surface of a semiconductor on the refraction phase of an optical beam is investigated. Both the density and effective mass of the surface state electrons can be controlled by a transverse electric field. While the surface density of electrons varies slowly with the applied field, their effective mass changes instantaneously. Therefore, a high bandwidth for the phase modulation can be obtained. It is expected that the device operates in the far-infrared region with a semiconductor as the base material. GaAs is one of the best candidates having both large dynamic range, and large ratio of free electron to the crystal effective mass. The device operates in a waveguide configuration, as discussed throughout the paper. The electron effective mass is found through quantum mechanical calculations, and the interaction with the incident light beam is treated classically. Finally, a waveguide light phase modulator is proposed.