Optically controlled characteristics of a new heterojunction field effect transistor

A new heterojunction field effect transistor has been proposed and studied analytically to investigate its suitability as a high speed optical detector. The characteristics of the device have been studied in the dark as well as in the illuminated conditions. In the new structure the Schottky gate of a typical high electron mobility transistor (HEMT) has been replaced by a junction gate in order to facilitate the absorption of optical radiation. The performance of the new device has been compared with that of the existing HEMT structure for similar application. It is seen that the absorption of optical radiation of suitable wavelength in the larger bandgap material results into conductivity modulation of the channel giving rise to a considerable change in the saturation drain current in illuminated conditions. This enables the device to respond to an intensity modulated optical signal. It has further been observed that due to an increased optical absorption region the modified structure shows a much better optical sensitivity than the existing one.     

The contribution of space charge in a high non-homogenous electric field to the creation of negative differential conductivity

The paper describes anomaly origination on current or voltage characteristics in time of positive potential on small curvature radius electrode rod against plane electrodes. An anomaly phenomenon occurred in the narrow voltage area in a high non-homogenous electric field close to the electrode (E > 10⁷ V m^?1). A mathematical – physical analysis of the observed processes in close proximity to the electrode with the above mentioned form is made. The differential equations, which analytically and theoretically describe this phenomenon, are compiled and solved. The space charge created by element particles (electrons, ions) which causes negative differential conductivity origination in narrow voltage area by their behaviour in electric field, plays a substantial role in this phenomenon. Current–voltage characteristics at both polarities of corona electrode were continuously measured at the study of static and dynamic processes occurring during discharge in the surrounding of a small curvature radius electrode. It was proved that an anomaly, in the form of negative differential conductivity (dI/dU < 0), appeared on a highly curved electrode at positive polarity in a narrow voltage area. This phenomenon was subjected to detailed experimental research including investigation of the influence of the shape and material of the electrode (output voltage), electrode temperature, influence of photoionization on the profile of the anomaly, the contribution of exoelectrons to particle distribution, and study of electrochemical potential of metal electrode. Oscillation of low ionized plasma at positive and negative polarity of small curvature radius electrodes has been analyzed. At the same time, the influence of the external forced electric field on the change of current–voltage characteristic profile was investigated. Theoretical justification of the anomaly phenomenon resulted from a change of energy conditions in the investigated place (the distance limit from the electrode is 10^?4–10^?6 m).     

MOS transistors with epitaxial Si,laterally grown over SiO2 by liquid phase epitaxy

We describe the first MOS transistors fabricated in silicon-on-insulator layers, obtained by liquid phase epitaxial lateral overgrowth of Si over SiO₂. Growth is performed around 930°–920° C using indium as a solvent. The layers are therefore p-type and have a doping of 4·10¹⁶ cm^–3. Electron mobilities of 540 cm²/Vs are obtained in the inversion channel; the threshold voltage of transistors with a gate length of 14.1 m is 510 mV. Our data demonstrate the applicability of liquid-phase epitaxial Si grown over oxidized Si for future use in three-dimensional integrated-device processing.     

Phonon-assisted tunneling and shot noise in double barrier structures in a longitudinal magnetic field

The phonon-assisted resonant tunneling is studied for the double barrier structures in a longitudinal magnetic field. Using the scattering matrix approach with an appropriate one-particle Green's function we are able to calculate the current and the zero frequency shot noise power spectrum in a large range of the magnetic field and to any order of the electron-phonon interaction. Obtained results describe well the relevant experimental data and provide new suggestions for further examinations.     

Influence of electric field on heterogeneous reactions stimulated by laser light

We present experimental data for vanadium and copper oxidation by cw CO₂ laser light in an external electric field. Direct influence of the external field on the crystallisation process has been demonstrated in both vanadium and copper cases; the oxidation rate and surface morphology depend sensitively on the sign and strength of the external field.     

Low-cost 3D nanocomposite solar cells obtained by electrodeposition of CuInSe2

Thin CuInSe₂ films have been prepared by electrodeposition from a single bath aqueous solution on both dense and nanoporous TiO₂. The films are deposited potentiostatically using a N₂-purged electrolyte at different potentials. Various deposition times and solution compositions have been employed. The effect of annealing in air and in argon at different temperatures and times is also investigated. Thin films and nanocomposites of TiO₂ and CuInSe₂ have been studied with electron microscopy, X-ray diffraction, Raman spectroscopy, and optical absorption spectroscopy. After a thermal anneal in argon at 350 °C for 30 min excellent CuInSe₂ is obtained. In particular the nominal crystal structure and the bandgap of 1.0 eV are found. Although pinholes are present occasionally, good samples with diode curves showing a rectification ratio of 24 at ±1 V are obtained. Upon irradiation with simulated solar light of 1000 W m⁻² a clear photoconductivity response is observed. Furthermore, also some photovoltaic energy conversion is found in TiO₂|CuInSe₂ nanocomposites.     

Pair creation by a photon in an electric field

The process of pair creation by a photon in a constant and homogeneous electric field is investigated basing on the polarization operator in the field. The total probability of the process is found in a relatively simple form. At high energy the quasiclassical approximation is valid. The corrections to the standard quasiclassical approximation (SQA) are calculated. In the region of relatively low photon energies, where SQA is unapplicable, the new approximation is used. It is shown that in this energy interval the probability of pair creation by a photon in electric field exceeds essentially the corresponding probability in a magnetic field. This approach is valid at the photon energy much larger than the “vacuum” energy in electric field: ω?eE/m. For smaller photon energies the low energy approximation is developed. At ω?eE/m the found probability describes the absorption of soft photon by the particles created by an electric field.     

Pair creation in the field of a moving charge

We consider the creation of fermion and boson pairs in the field of a charge moving in a circle. We show that the effect is observable for χ=(Ω/m)(E/m_Q)²～ 1.     

Magnetoquantum transport in a modulated 2D electron gas with spin-orbit interaction

We investigate the effects of spin-orbit interaction (SOI) and plane-perpendicular magnetic field on the conductivity of a two-dimensional electron system in the presence of one-dimensional electrostatic modulation. The calculations are performed when a low-intensity, low-frequency external electric field is applied. The Kubo formula for the conductivity is employed in the calculation. The single-particle eigenstates which depend on the strengths of the magnetic field, the SOI and modulation potential, are calculated and then used to determine the conductivity. We present numerical results for the conductivity along the channels as well as the tunneling conductivity perpendicular to the constrictions as functions of the modulation potential, the SOI and the magnetic field. We demonstrate that the effect of finite frequency is to related to the reduction of both the longitudinal and transverse conductivities.     

Rapid growth of ultra thin SiO2 films by a large-area electron beam

Rapid growth of ultra thin oxide films (40–180Å) of silicon using a low-energy large-area electron beam has been performed with a pressure ratio of 31 (O₂/He) and a total pressure of 0.5–0.7 Torr. A higher oxidation rate of about 625Ų/s is found for shorter irradiation time of the e-beam in the e-beam dose range 0.75–3 Coulomb/cm² and at lower substrate temperature 540–740°C. AES and XPS demonstrated a rapid electron-stimulated oxidation process of the Si surface. For the grown ultra thin oxide films, C-V characteristics, dielectric strength, uniformity of the film over the entire Si wafer and its thickness as a function of the processing time of the e-beam are also presented.     

Particle creation in a time-dependent electric field revisited

We adopt the general formalism for analyzing evolution of gaussian states of quantized fields in time-dependent backgrounds in the Schrodinger picture (presented in detail in Mahajan and Padmanabhan [G. Mahajan, T. Padmanabhan, Gen. Rel. Grav. 40 (2008) 661]) to study the example of a spatially uniform electric field background (in a time-dependent gauge) which is kept turned on for a finite duration of time. In particular, we study the time-dependent particle content, defined in terms of the concept of instantaneous eigenstates, and describe how it captures the time evolution of the quantized field modes. The actual particle creation process occurs over a relatively short interval in time, and the particle content saturates rather quickly. We also compare the power spectrum of the field modes, computed in the asymptotic limit, with the corresponding situation in a cosmological de Sitter background. Particle creation under the influence of a spiked electric field localized in time, as a particular limiting case of the above general model, is also considered.     

Laser-induced damage in SiO2 and CaF2 with picosecond and femtosecond laser pulses

Single- and multiple-shot damage thresholds and plasma-emission thresholds for fused silica and CaF₂ are reported for 790 nm photons as a function of laser pulse width (190 fs – 4.5 ps). The results are compared with single-shot plasma-emission measurements [1] and with multiple-shot damage measurements [2]. Both the damage threshold and the plasma-emission threshold are shown to decrease with decreasing pulse width over the entire pulse-width range investigated.     

Defect reduction and surface passivation of SiO2/Si by heat treatment with high-pressure H2O vapor

Heat treatment with high-pressure H₂O vapor was applied to improve interface properties of SiO₂/Si and passivate the silicon surface. Heat treatment at 180–420 °C with high-pressure H₂O vapor changed SiO_x films, 150 nm thick formed at room temperature by thermal evaporation in vacuum, into SiO₂ films with a Si-O-Si bonding network similar to that of thermally grown SiO₂ films. Heat treatment at 130 °C with 2.8×10⁵ Pa H₂O for 3 h reduced the recombination velocity for the electron minority carriers from 405 cm/s (as-fabricated 150-nm-thick SiO_x/Si) to 5 cm/s. Field-effect passivation was demonstrated by an additional deposition of defective SiO_x films on the SiO₂ films formed by heat treatment at 340 °C with high-pressure H₂O vapor. The SiO_x deposition reduced the recombination velocity from 100 cm/s to 48 cm/s. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Passivation of n-GaAs (100) surface by a Langmuir-Blodgett film

We report the results of passivation of n-GaAs surface by Langmuir-Blodgett films. The capacitance-voltage and current-voltage characteristics in a metal-insulator-semiconductor configuration fabricated using films as insulators, show that the frequency dispersion of the accumulation capacitance is small, indicating that the high frequency capacitance under accumulation is due to the LB film. It has been shown that it reduces the surface barrier characteristic of GaAs surfaces, and may offer hope for unpinning the surface Fermi level. We offer a possible explanation for these findings in terms of the advanced unified defect and the effective work function models.     

The coalescence of silicon layers grown over SiO2 by liquid-phase epitaxy

We have investigated by liquid-phase epitaxy (LPE) the coalescence of defect-free silicon-on-insulator (SOI) layers. The SOI lamellae grow out laterally from neighbouring seeding windows and spread over the SiO₂. In our study, the seeding window edges are straight. The long window edges are parallel and extend in the (111) substrate plane in direction. Coalescence of SOI lamellae takes place without the formation of defects whenever it begins at one point and then proceeds in directions parallel to the longer edges of the windows in a zip-like mechanism. Defect-free coalescence seams reach lengths of up to 150 m.     

Effect of interface states on negative capacitance characteristics in GaAs homojunction far-infrared detectors

Bias-, frequency- and temperature-dependent capacitance characteristics of p-GaAs homojunction interfacial work-function internal photoemission (HIWIP) far-infrared detectors are reported. A strong negative capacitance phenomenon has been observed. The origin of this effect is believed to be due to the carrier capture and emission at interface states, and has been confirmed by a comparison study of capacitance characteristics on p-GaAs HIWIP detectors with different interface state densities. A fitting data based on charging–discharging current and the inertial conducting current model show good agreement with the experimental observations. Received: 15 November 1999 / Accepted: 20 April 2000 / Published online: 5 October 2000     

Erratum to: Peculiarities of pair creation by a peak electric field

Russian Physics Journal -     

长直带电导体柱的电场及其电荷面密度

通过保角变换法及其变换关系,求解长直带电导体柱的电场分及电荷面密度,利用数学软件MATLAB对其场分布进行数值模拟,并绘制出电荷面密度的分布曲线.     

Arc plasma jet cleaning of the silicon surface before CoSi2/Si contact formation

Cleaning of the silicon surface before Co film deposition is a key procedure in the synthesis of silicide (CoSi₂) and, hence, in the production of the metal-semiconductor contact. This study deals with a new method of surface cleaning using arc plasma jet treatment (APJT) at atmospheric pressure. The results show that cleaning of the Si surface using APJT (Ar/CCIF₃) improves the Schottky barrier contact parameters in comparison with conventional wet HF final cleaning and additional cleaning using in situ Ar-ion-beam sputter etching. Moreover, substantially longer time of wafer exposure to air between final cleaning and metal deposition is acceptable. Auger electron spectroscopy shows that APJT removes oxygen from the Si surface.