Chihiro Hamaguchi

STUDY OF INTERFACE ROUGHNESS DEPENDENCE OF ELECTRON MOBILITY IN SI INVERSION LAYERS USING THE MONTE CARLO METHOD

The electron mobility in the inversion layer of a metal–oxide semiconductor field effect transistor formed on the (100) silicon surface is calculated by using a Monte Carlo approach which takes into account size quantization, acoustic phonon scattering, intervalley phonon scattering and surface roughness scattering. Degeneracy is also considered because it is important at higher normal effective fields (high gate voltages). The main emphasis is placed on the influence of the specific autocovariance function, used to describe the surface roughness, on the electron mobility. Here we compare the mobilities obtained using exponential and Gaussian autocovariance functions. It is found that the electron mobility calculated with roughness scattering rates based on the exponential function shows good agreement with experiments. The effect of the degeneracy and screening on the roughness scattering is also discussed.

Contact and distributed effects in quantum well infrared photodetectors

We propose a simple distributed model for intersubband quantum well infrared photodetectors (QWIPs), which explicitly takes into account the injecting properties of the contacts. We show that the QWIP operation with multiple QWs involves the formation of a high‐field domain near the emitter, caused by the modulation of the bound electron density in the QWs by applied voltage and infrared radiation. The external characteristics of the QWIP (total current, differential resistance, and quasistatic capacitance) are strong functions of the voltage and radiation intensity.

A comparison of numerical solutions of the Boltzmann transport equation for high-energy electron transport silicon

In this work we have undertaken a comparison of several previously reported computer codes which solve the semiclassical Boltzmann equation for electron transport in silicon. Most of the codes are based on the Monte Carlo particle technique, and have been used here to calculate a relatively simple set of transport characteristics, such as the average electron energy. The results have been contributed by researchers from Japan, Europe, and the United States, and the results were subsequently collected by an independent observer. Although the computed data vary widely, depending on the models and input parameters which are used, they provide for the first time a quantitative (though not comprehensive) comparison of Boltzmann Equation solutions. >

High-Sensitivity SOI MOS Photodetector with Self-Amplification

A high-sensitivity silicon-on-insulator (SOI) metal-oxide-silicon (MOS) photodetector compatible with conventional silicon technology is proposed. Its operation principle is based on that of a lateral bipolar transistor in spite of an SOI MOS device structure. Photodetectors with narrow base width or short channel length have high current gain which is attributed to a self-biased effect under illumination. Current gain as high as 100 has been achieved for the device with a channel length of 1.0 µm. Measured intrinsic response time for optical pulses is 19 µs for the photodetector with a channel length of 0.7 µm.

Theoretical model for self-interstitial generation at the Si/SiO2 interface during thermal oxidation of silicon

Using a grating pattern of parallel nitride and oxide stripes on the silicon surface, self‐interstitial concentration at the Si/SiO2 interface is accurately determined by means of oxidation‐induced stacking fault growth observation. The results show that the interstitial concentration at the interface is found to be determined by the oxidation of interstitials in the oxide rather than self‐interstitial diffusion in bulk silicon. A newly proposed physical model incorporates the balance among the generation rate of interstitials at the oxidizing interface, the annihilation rate of interstitials due to surface regrowth, and the rate at which they diffuse into the oxide and react with incoming oxidants. For higher oxidation rates, the model predicts that the interstitial concentration follows a 0.5 power dependence on oxidation rate. For slower oxidation rates, the concentration at the interface becomes lower than the equilibrium interstitial concentration, leading to the oxidation‐retarded diffusion of dopan...

Density relaxation of silicon dioxide on (100) silicon during thermal annealing

Measurements of the refractive index of thermally grown oxide after annealing reveal that the density relaxation of the oxide is well described by a stretched exponential decay function. The experiments of two‐step oxidation show that oxygen diffusivity in the oxide exponentially decreases with the oxide density. The relation between the oxide density and the refractive index is well expressed by a simple power relation rather than the Lorenz–Lorenz formula.

A model of impact ionization due to the primary hole in silicon for a full band Monte Carlo simulation

The rate of impact ionization due to the primary hole in silicon is numerically derived from pseudo‐wave‐functions and realistic energy band structure based on a nonlocal empirical pseudopotential method including the spin‐orbit interaction. The calculated impact‐ionization rate SII [s−1] is well fitted to an analytical formula with a power exponent of 3.4, indicating a soft threshold of the impact ionization rate: SII [s−1]=1.14×1012 [s−1 eV−3.4]×(e [eV]−1. 49 [eV])3.4, where e [eV] is the energy of the primary hole relative to the valence band edge. The soft threshold originates from the complexity of the silicon band structure. The calculated impact‐ionization rate shows strong anisotropy at low hole energies (e<3 eV), while it becomes isotropic at high hole energies, indicating the isotropy of the joint density of states at high energies. Numerical calculation also makes it clear that average energies of secondary generated carriers e depend linearly on primary hole energies at the moment of their ge...

Electron Mobility in Si Inversion Layers

Gate voltage dependence of electron mobility in n-channel MOSFETs is investigated using Hall effect and channel conductance measurements at room temperature and at 77 K. The electron mobilities obtained by the two different methods show a good agreement with each other and exhibit a decrease with increasing gate voltage in the region of high effective normal field. The theoretical model for electron mobility is given based on the interactions of two-dimensional electron gas confined in the inversion layer with acoustic phonons, intervalley phonons, surface-roughness and ionized impurities. An analytical expression is obtained for the electron mobility, where three types of f- and g-intervalley phonons are included. The calculated results show a good agreement with the experimental data and the decrease in the mobility at high effective normal field is interpreted in terms of surface-roughness scattering which results in Eeff-2 dependence at high normal fields.

Optical Properties 1

This chapter deals with fundamental theory of optical properties in semiconductors. First reflection and absorption coefficients are derived by using Maxwell’s equations. Then quantum mechanical derivations of direct and indirect optical transition rates are given in addition to the classification of the joint density of states. Optical transitions associated with electron-hole pair, excitons, are also discussed. Dielectric functions are discussed in connection with the critical points of semiconductors. Also we will discuss stress effect on the optical transition such as piezobirefringence and stress-induced change in the energy band structure. The results are used in Chap. 9 to evaluate the strain effect in quantum well lasers.

Analytical Device Model of SOI MOSFETs Including Self-Heating Effect

A simple analytical model for device characteristics of silicon-on-insulator (SOI) MOSFETs is proposed. The effect of the self-heating is incorporated into a pseudo-2-dimensional drain-current model through an analytical expression using a thermal distribution-constant circuit. The device characteristics calculated with the model were found to agree well with experimental drain-current characteristics.