Demonstration of thermal poling in holey fibres

A second-order nonlinearity is induced for the first time in a holey fibre by thermal poling. Non-phase matched second harmonic generation with a ~10^-8/W conversion efficiency is observed and the electro-optic coefficient is measured to be ~0.02 pm/V     

Modification of thermal poling evolution using novel twin-holefibers

Thermal poling current and electrooptic evolution were studied for a standard twin-hole fiber and two novel design twin-hole fibers. The poling characteristics were modified in the novel fibers, which had a trap or donor region inside the anode hole. Modifications of the poling characteristics were observed in both the current evolution and the electrooptic evolution. The novel fiber designs can facilitate the tailoring of poled fiber device characteristics     

Method to improve thermal poling efficiency in silica glasses

For the first time, thermal polings are performed on Suprasil I samples (Heraeus) under square alternating voltages at variable frequency. Experimental results exhibiting a large increase (×13 compared to a continuous voltage poling) of the second-harmonic signal generated within a sample poled at a frequency of 1 mHz are presented     

Evidence of bandgap-narrowing in the space-charge layer of heavily doped silicon diodes

The gradient voltage has been measured for seven heavily doped, graded-junction silicon diodes at 300 K. Experimental values up to nearly 0.5 V lower than conventional theoretical predictions have been observed. The lowering is attributed to bandgap-narrowing in the space-charge region. This narrowing is expected to be much larger than in neutral material of the same doping density because of the absence of free-carrier screening.     

Allowance for relativistic effects in space-charge spreading of an electron beam

Hollway's determination of the optimum spot size (limited by space-charge spreading) at a target is extended to include higher voltages (above 10kV). His computed data can be used to determine optimum target-spot sizes over the range 0.019 相似文献   

Progress in creating second-order optical nonlinearity in silicate glasses and waveguides through thermal poling

This paper describes progress in characterizing the distribution and localization of the second-order nonlinearity induced in thermally poled silicate glasses and optical waveguides, in particular, optical fibers. It starts by describing the basics of the poling technique, especially the most commonly used "thermal poling" technique. Then results of systematic investigation of the distribution of the second-order nonlinearity in poled glass and special fibers using second-harmonic microscopy are presented. Interesting issues such as the effectiveness of the poling technique for waveguides formed by ultrafast laser pulses are also discussed.     

Lateral space-charge effects on ballistic electron transport across graded heterojunctions

Hot electron transport across graded compound semiconductor heterojunctions has been explored using a two-dimensional formulation of the self-consistent ensemble Monte Carlo method. The Al_xGa_1-xAs/GaAs heterojunction imbedded into a vertical field effect transistor with two ohmic contacts (source, drain) and two lateral Schottky gates has been used as an example. Lateral space charges modulated by the gates are shown to control ballistic injection of electrons over the heterojunction under steady state conditions. The transient response to a gate pulse is found to be determined by carrier transit from the heavily doped source contact region into the channel. A conceptual one-dimensional section model is used to explain the Monte Carlo results.     

高阶空间电荷场对匹配高斯光束自偏转特性的影响

通过数值模拟的方法,研究了高阶空间电荷场对匹配高斯光束在光伏光折变晶体中自偏转特性的影响。结果表明,对于给定的与晶体参量匹配的高斯光束,高阶空间电荷场对其自偏转特性的影响与外电场和光伏场的极性和强度,以及入射光束的强度有关。当外电场、光伏场、入射光束的强度取不同的参数组合时,就可以控制高斯光束的偏转程度,在三者特定的参数组合下,还可以实现高斯光束偏转方向的改变,进而实现高斯光束的无偏转稳定传播。     

An analysis of thermal and space-charge spreading of electron beams from Guns of the pierce type

An existing technique for analyzing the spreading of an electron beam in a drift space is extended to be valid for regions with an arbitrary variation of potential. Equations enabling the complete profile of the beam to be computed are presented.     

Vacuum poling: an improved technique for effective thermal polingof silica glass and germanosilicate optical fibres

The use of thermal poling in a vacuum to eliminate the spreading out of the poled regions beyond the boundaries of the positive electrode is proposed and experimentally demonstrated. A substantial improvement in reproducibility and quality of the induced second-order susceptibility is achieved     

Radiation-induced space-charge buildup in MOS structures

An analysis of a simple model for radiation-induced space-charge buildup in the SiO2layers of MOS structures has been carried out. The model assumes that hole-electron pairs are created in the SiO2by the radiation and that some of the electrons thus created drift out of the SiO2layer under the action of an applied potential across the oxide, VG, while the corresponding holes become trapped. The diffusion of electrons is assumed to be negligible. The analysis predicts 1) a dependence of charge buildup on radiation doseD, approximately of the form (1 - e^{-beta D}); 2) a linear dependence of the charge buildup on VG, for both polarities of VG; and 3) the dependence of the charge buildup on the total dose absorbed and not on the rate at which the dose was received. Experimental observations on the SiO2layers found in commercial MOS-FET's show good general agreement with the predictions of the analysis. To obtain quantitative agreement, however, it was necessary to assume that the mobility-lifetime product for electrons in the oxide is much lower at the SiO2-Si interface than at the SiO2- metal interface. Other discrepancies were observed but they can be explained as the result of oversimplifications employed in the analysis. In particular, it was necessary to postulate that under some circumstances diffusion of electrons out of the oxide was important and that, in addition to holes, a small number of electrons may be trapped in the oxide in some cases. The space charge was found to accumulate within ≤ 200 Å of the cathode-oxide interface.     

Dynamics of moving space-charge domains in germanium

We report the experimental measurement of moving space-charge domains in liquid He cooled ultrapure p-Ge using a movable capacitive probe to map the one-dimensional potential, electric field and space charge distributions along the conduction direction of rectangular samples at successive times. The data show dipole-type domains moving periodically through the sample in the direction of applied dc electric field.     

Electron space-charge effects on high-frequency performance ofAlGaAs/GaAs HBTs under high-current-density operation

The high-frequency characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) under high-current-density biasing condition are investigated in conjunction with the electron space charge in the collector depletion layer. A significant increase in cutoff frequency f_t and maximum oscillation frequency f_max at the early stage of the base push-out was observed in HBTs with a lightly doped n-type collector structure, and is attributed to the collector depletion layer widening and the enhancement of the velocity overshoot effect caused by the increasing electron density     

Surface space-charge waves in open guiding structures

Basic definitions related to the main electrodynamic characteristics of surface space-charge waves are formulated. These characteristics and their relationships with the geometric dimensions of guiding structures (a dielectric cylinder and a planar metal-dielectric waveguide) are determined.     

Hydrogen-induced surface space-charge regions in oxide-protected silicon

This paper presents data on the effects of hydrogen heat treatments on oxide-protected silicon. The test vehicle is a metal-oxide-semiconductor (MOS) transistor with its metal gate electrode not yet attached. The device was exposed to a hydrogen-containing atmosphere for various times and temperatures, and the resultant channel resistances were monitored. These resistances were then normalized to sheet resistivities. The experimental techniques and some of the problems encountered are discussed, as well as early application of the data to MOS and bipolar devices.     

Two-point boundary-value problems in theories of space-charge conduction

A computational technique is described which overcomes numerical difficulties reported previously in the literature in the solution of time-independent space-charge conduction problems that involve three dependent variables. By way of illustration, results are presented for a model describing electron injection into a ptype semiconductor.     

Monte-Carlo simulation of space-charge injection FET

Results of Monte-Carlo simulation of a new type of transistor, the space charge injection FET, are reported. Owing to the use of submicron undoped active regions, it seems possible to achieve low values of gate capacitance associated with high values of transconductance leading to a gain-bandwidth product close to the submillimetric wavelength range.     

A new quasi-static model of space-charge limiting

The classical quasi-static model of space-charge limiting estimates time averages of the potential distribution and the current flow. But numerical studies by Birdsall and Bridges have indicated important limitations in the classical model. In particular, it makes no estimate of the fluctuation in the electric field. This paper proposes an alternative model that does estimate the fluctuation. The model leads to a pair of coupled second-order equations that closely resemble the classical equations. First-order solutions are obtained by an iterative process. The location of the points of zero field are only in fair agreement with the values obtained by discrete-charge methods, but the predicted fluauation in the peak electric field is considerably better. In particular, the model predicts a much larger fluctuation at the anode than at the cathode (for currents near the threshed of instability) in agreement with Birdsall and Bridges' numerical results.     

Unified treatment of small-signal space-charge dynamics in bulk-effect devices

Space-charge dynamics in semiconductors with negative differential mobility are discussed in a small-signal approximation taking account of the role of carrier diffusion and are shown to exhibit fundamentally four different properties. These differences originate from two conditions, one being the direction of propagation of the space-charge wave and the other being whether the space-charge wave is characterized by frequency-independent velocity (convective instability) or frequency-independent wavelength (absolute instability). These behaviors of space-charge waves have a great influence on the performance of bulk-effect devices and give rise to extremely different characteristics. When the space-charge wave is characterized by frequency-independent velocity, two-terminal impedance of bulk-effect devices shows the conventional transit-time effect. On the contrary, the property of space-charge waves characterized by frequency-independent wavelength gives rise to the static negative resistance in two-terminal impedance.