Table of contents

This paper presents an experimental case study of an embedded CMOS analogue IP core for SOC applications. Based on the research and analysis of embedded analogue IP core characteristics and design specification, the embedded voltage reference IP core is implemented by adopting a high speed self-bias amplifier and the sub-threshold characteristics of MOSFETs. The core has the advantages of temperature compensation and width supply source voltage, and the output voltage of reference can be flexibly changed by adjusting the resistor. The IP core was implemented by TSMC 0.35 µm, 0.25 µm and 0.18 µm CMOS technology. The measured results show a temperature coefficient of less than 15 ppm K⁻¹ and power current of less than 5.2 µA. Finally, the design methodology of the embedded CMOS analogue IP core is summarized.

High-speed single transverse mode 850 nm vertical cavity surface emitting lasers (VCSELs) with large emission aperture with a diameter of 8 µm were fabricated. These VCSELs exhibit good performance with threshold currents of 1.5 mA, a single transverse mode emission within the full operational range and a maximum output power of 3.8 mW. The large aperture is advantageous to these VCSELs with a smaller dynamic resistance (60 Ω) than that of conventional single-mode VCSEL. These single-mode VCSELs also demonstrate superior high-speed performance up to 10 Gb s⁻¹.

The unrestricted Pople–Nesbet approach for real atoms is adapted to quantum dots under applied magnetic field. Gaussian basis sets are used instead of the exact single-particle orbitals in the construction of the appropriated Slater determinants. Both system chemical potential and charging energy are calculated, as well as the expected values for total spin and its z-component. We have verified the validity of the energy shell structure as well as the Hund rule for state population at zero magnetic field. Above given fields, we have observed a violation of the Hund rule by the suppression of triplet and quartet states at the 1p-energy shell, taken as an example. We have also compared our present results with those obtained by using the LS-coupling scheme for low electronic occupations. We have focused our attention on ground-state properties of GaAs quantum dots populated up to 40 electrons.

n-type GaSb has been prepared by metal-organic chemical vapour deposition with tellurium donors using diethyltelluride as the dopant precursor. The maximum carrier concentration achieved was 1.7 × 10¹⁸ cm⁻³, as measured by van der Pauw–Hall effect measurements, for an atomic tellurium concentration of 1.8 × 10¹⁹ cm⁻³. The apparent low activation of tellurium donors is explained by a model that considers the effect of electrons occupying both the Γ and L bands in GaSb due to the small energy difference between the Γ and L conduction band minima. The model also accounts for the apparent increase in the carrier concentration determined by van der Pauw–Hall effect measurements at cryogenic temperatures.

In this paper, we present a new approach for separating the bulk lifetime and surface recombination velocities via a single laser microwave photoconductance. When a pulsed laser pumps on the probed sample, with the illumination of first the front surface and then the back surface with the same light wavelength, the bulk lifetime and the surface recombination velocities are obtained. Detailed theoretical analysis and preliminary experimental results are shown to demonstrate the applicability of the method.

Waveguide phase matching of a frequency conversion process within an isotropic semiconductor is studied. The three-wave interaction involves pump and signal beams in the near infrared, and the idler at THz frequencies, i.e. with a wavelength greater than 50 µm in GaAs. Phase matching is obtained by exploiting modal dispersion and, for energies below the reststrahlen region, the semiconductor anomalous dispersion. This original phase matching scheme provides simultaneously a long interaction length, due to waveguide confinement, and efficient wave mixing because only the fundamental modes are involved in a modal phase matching process. Two different types of waveguides are studied: bulk semiconductor rods and plasmon waveguides.

Laterally-coupled distributed feedback (LC-DFB) laser diodes made without an epitaxial re-growth process have the advantage of a simple fabrication process. In this paper, two-dimensional optical field distribution of the fundamental quasi TE (transverse electric) mode is calculated by means of a semivectorial finite-difference method (SV-FDM). The dependence of the effective coupling coefficient (κ_eff) on the dutycycle of first-, second- and third-order LC-DFB LDs is investigated using modified coupled wave equations.

The electrical and structural properties of Ti/W/Au ohmic contacts to moderately doped n-GaN (4.07 × 10¹⁸ cm⁻³) have been investigated. The as-deposited and annealing contacts at temperatures below 750 °C exhibit non-linear behaviour. However, the contact showed ohmic behaviour after annealing at a temperature in excess of 850 °C. Specific contact resistance as low as 8.4 × 10⁻⁶ Ω cm² is obtained from the Ti(12 nm)/W(20 nm)/Au(50 nm) contact annealed at 900 °C for 1 min in N₂ ambient. It is observed that annealing results in a large reduction (by ∼160 meV) in the Schottky barrier height of the contacts, compared to the as-deposited one. The atomic force microscopy results showed that the surface morphology of the contact annealed at 900 °C is fairly smooth with a RMS roughness of 3.8 nm. Based on the Auger electron spectroscopy and glancing angle x-ray diffraction results, possible explanations are given to describe the annealing temperature dependence of the specific contact resistance of the contacts.

The successive ionic layer adsorption and reaction method was used to deposit CdSe thin films on glass substrates at room temperature (300 K). The films were characterized by x-ray diffraction, energy dispersive x-ray analysis, scanning electron microscopy, atomic force microscopy and high-resolution transmission electron microscopy. Optical absorption and electrical resistivity were measured. The CdSe layer grew with nanocrystalline cubic phase along with some amorphous phase present in CdSe film, with an optical band gap 'E_g' of 2.1 eV and room temperature electrical resistivity of the order of 10⁶ Ω cm.

The performance of specific on-state resistance (R_on,sp) versus breakdown voltage (V_br) of a superjunction power MOSFET device is constrained by the quality of its sidewall junctions formed by neighbouring p and n columns in the drift region. The p–n junction quality, which is inevitably affected by the inter-column dopant diffusion in practice, will limit the R_on,sp–V_br device performance if no compensation measure is taken. A detailed study of the influence of sidewall junction quality on performance at various column widths under given thermal process conditions was carried out through process and device simulations. The study discovers the practical optimal performance of superjunction (SJ) DMOS and UMOS structures under the influence of dopant inter-column diffusion. Analysis of the phenomenon shows that the degradation of the breakdown voltage is caused by the p and n column charge imbalance. Practical SJ performance equations, which model the influence reasonably well, are derived in the paper. These equations can be used to predict the practical performance of an SJ device under given thermal conditions, which in turn guides us to the compensation measures required to achieve better performance.

A comprehensive, fully self-consistent, optical–electrical–thermal gain, three-dimensional model of edge-emitting nitride diode lasers has been generalized to simulate a room temperature (RT) continuous-wave (CW) threshold operation of possible designs of a one-dimensional array of these lasers. Nitride A^IIIN materials exhibit higher thermal conductivities than arsenide A^IIIAs ones. Nevertheless, an operation of possible nitride arrays has been surprisingly found to be more influenced by thermal interactions between their emitters than in arsenide ones. Therefore, emitters in nitride arrays should be arranged more sparsely to enable their efficient RT CW operation.

Growth of CdS_0.08Se_0.92 nanocrystals embedded in glass is studied through the combinative analysis of optical absorption and photoluminescence (PL) spectroscopy at room temperature. The quantum confinement effect is observed in these structures. Average nanocrystal radii are found to be in the range of 2.3–4.2 nm with the help of a quantized state effective mass theory. Photoluminescence spectra are studied by means of the model of Ravindran et al (1999 Nanostruct. Mater.11 603). The difference between the energies of the deep trap peak and first exciton peak is found to be ∼0.2–0.3 eV. The possible sources of the overall shift in these peaks are also discussed.

We investigate the near-threshold properties of a two-dimensional curved-grating distributed-Bragg reflector laser provided with high transverse confinement. All fields are described in the spectral domain in the frame of an extended (3 × 3) transfer matrix formalism which takes into account the internal sources, as well as saturation of the gain medium through amplified spontaneous emission.

CuIn_0.5Al_0.5Se₂ thin films are successfully prepared using a four-source co-evaporation technique on soda-lime glass substrates held at a substrate temperature of 673 K. Powder x-ray diffraction studies reveal that the films are polycrystalline in nature with chalcopyrite structure. The optical band gaps, calculated from spectral transmittance data, are found to be 1.56 ± 0.02 eV, 1.60 ± 0.02 eV and 1.85 ± 0.02 eV. Considering the three fold optical structure of chalcopyrite compounds, these are attributed to fundamental absorption and additional transitions arising out of crystal field and spin–orbit interactions. The crystal field (Δ_CF) and spin–orbit (Δ_SO) splitting parameters deduced from these optical band gaps are found to be −0.06 eV and 0.26 eV, respectively. The deformation potential estimated by using a quasi-cubic model is found to be −2.0 eV. The percentage of hybridization of the orbitals was determined using a linear hybridization model. The films are p-type conducting with a room temperature resistivity of 80 Ω cm.

Indium hydroxide (In(OH)₃) nanorods have been synthesized via a novel hydrothermal process at 200 °C without addition of any surfactant. X-ray diffraction (XRD) patterns show that the nanorods are indium hydroxide. The selected area electron diffraction (SAED) patterns indicate that the In(OH)₃ nanorods are single crystalline in nature. Furthermore, the growth mechanism of hydrothermal synthesis of In(OH)₃ nanorods has been preliminarily presented.

We report on the energy and momentum relaxation of hot electrons in n-type epilayer InN grown on sapphire substrate using molecular beam epitaxy (MBE). Hall and pulsed I–V measurements are carried out in the temperature range between 77 and 300 K. Drift velocity versus electric field characteristics show that, at 77 K, the drift velocity saturates just above v_d ∼ 8 × 10⁶ cm s⁻¹ at electric fields in excess of E ∼ 12 kV cm⁻¹. The mobility comparison method together with the power balance equation is used to obtain the electron temperature as a function of applied electric field and the electron energy loss rate as a function of electron temperature. Our results show conclusively that the effective energy relaxation time constant in InN is 200 fs. This is about six times slower than the theoretical value for the e–LO phonon scattering time of 31 fs. The effects of non-equilibrium phonon generation on slowing down of the energy relaxation and increasing the momentum relaxation processes are discussed using a theoretical model first developed for GaAs and then adapted to the III-N material systems.

NPN transistors were irradiated by 95 MeV oxygen ions in a fluence ranging from 5 × 10¹⁰ to 5 × 10¹² ions cm⁻². The dc current gain (h_FE), excess base current (ΔI_B = I_Bpost − I_Bpre), excess collector current (ΔI_C = I_Cpost − I_Cpre) and collector-saturation current (I_CS) of the ion-irradiated transistors were studied systematically. We found that both h_FE and I_CS of the transistors decrease drastically after ion irradiation. Secondly, a significant increase in the collector current (I_C) along with the increase in the base current (I_B) after ion irradiation was observed. The radiation-induced trap levels in the collector–base depletion region of NPN transistors were studied by employing the deep level transient spectroscopy technique and different types of trap levels were observed. The results obtained on the activation energy, density of trap levels, apparent capture cross section of the defects, introduction rate and space charge layer lifetime of different defects for different total fluence are presented and discussed.

GaSb photovoltaic cells are the most common choice for receivers in thermophotovoltaic (TPV) systems. Although nowadays their manufacturing technology is well established, a theoretical simulation frame for their modelling under real TPV operating conditions is still not fully developed. This is basically due to the lack of a reliable and accurate set of GaSb material parameters as input for the semiconductor simulation tools. Thorough GaSb TPV cell models are needed to understand the electro-optical behaviour of the cells and eventually are essential in improving their design. This work will try to go beyond this key issue, carefully analysing and reviewing some of the key parameters for GaSb. A complete set of material parameters, including revised values for the intrinsic concentration, the electron and hole mobilities and the absorption coefficient, is given based on extended reviews of previously published data. For the first time, estimations for their temperature dependences are introduced. Finally, GaSb TPV cells are manufactured and characterized inside a real TPV system prototype. The comparisons between the electrical measurements and the model theoretical predictions confirm the validity of the proposed set of GaSb material parameters and their temperature dependences.

In this paper, we report, for the first time, the fabrication and characterization of Si/SiGe doped-channel field-effect transistors (DCFETs) using an inductively coupled plasma (ICP) dry etching process. ICP can generate high-density plasma under low pressure, independently control plasma density as well as ion bombardment energy, give a better anisotropic etching profile and almost eliminate the parasitic current path between isolated devices. Experimental results show that the doped-channel FET using ICP mesa has higher breakdown voltage, lower leakage current, higher transconductance and larger current drivability as compared to devices fabricated using wet mesa etching.

Tin oxide (SnO₂) microfibres in the rutile structure were synthesized using electrospinning and metallorganic decomposition techniques. Fibres were electrospun from a precursor solution containing 20 mg poly(ethylene oxide) (molecular weight 900 000), 2 ml chloroform and 1 ml dimethyldineodecanoate tin, and sintered in the air for 2 h at 400, 600 and 800 °C, respectively. Scanning electron microscopy, x-ray diffraction and Raman microspectrometry were used to characterize the sintered fibres. The results showed that the synthesized fibres are composed of SnO₂.

A set of equations for calculating the probability for electric-field-induced interband transitions in periodic crystals (Krieger and Iafrate 1986 Phys. Rev. B 33 5494) can be used in combination with the full band Monte Carlo method to study high-field electronic transport properties in semiconductors. However, when the equations are applied to realistic cases in which the underlying band structure is obtained from numerical band structure programmes, the equations are not directly solvable because of the indeterminacy of the phases of the band structure Bloch wavefunctions. Here we discuss this problem and present a method for choosing the phases of the Bloch functions in such a way that the equations yield physically correct interband transition probabilities.

An analytical-band Monte Carlo model incorporating four non-parabolic spherical valleys to represent the first two conduction bands has been developed to model hot electron transport and impact ionization in GaAs. We have tested the performance of this simple model against full-band Monte Carlo simulations for calculating the probability distribution function of impact ionization path length, time and energy; and transient velocity overshoot at high fields. This simpler model is found capable of reproducing the full-band model results satisfactorily but at much lower computational cost.