Accurate analysis of multimode interference devices

The accurate analysis of multimode interference devices is demonstrated by using the least-squares boundary residual (LSBR) method. Accurate modal propagation constants and spatial field profiles in the multimode interference (MMI) section can be obtained by using the finite-element method. The accurate calculation of the excited modal coefficients is achieved by using the LSBR, which satisfies the continuity of the transverse field components more rigorously than the simple overlap integrals.     

Evidence of two-dimensional carrier confinement in thin n-channelSOI gate-all-around (GAA) devices

The effect of two-dimensional electron confinement is observed in thin-film, gate-all-around SOI transistors operated at low temperature. Physical 3D confinement in a thin silicon film using the silicon/gate oxide potential barrier (in contrast to heterojunction or electrostatic confinement) is shown for the first time. In these devices volume inversion gives rise to a 2DEG, and the population of the energy subbands can be controlled by the gate voltage. The position of transconductance peaks and valleys, corresponding to the population of different subbands as the gate voltage is increased, is in good agreement with theoretical predictions     

Radial confinement in lateral power devices

The aim of this paper is to demonstrate a novel, radial confinement approach to improve the breakdown performance of a lateral power device. The key feature is that the drift region width decreases gradually from the anode to the cathode to achieve charge confinement in the radial direction. As a result, the n⁻ drift region concentration can be increased by a factor of 7 in comparison to a conventional counterpart leading to a lower specific on-state resistance. This technique is applicable to silicon-on-insulator technologies, such as the SOI or SOS, and to high-voltage thin-film transistor technologies on glass. Experimental results from radial diodes fabricated in SOS technology show a blocking capability higher than from those of their conventional counterparts.     

Optical and confinement properties of two-dimensional photoniccrystals

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered     

Accurate time-domain analysis of microwave and optical signal interaction in electrooptic devices

This paper presents a novel formalism based on the application of the generalized telegrapher's equations to the modeling and designing of integrated electrooptical devices. In this approach, we eliminate the restrictions commonly introduced in the past, such as a weakly guiding condition and isotropic unperturbed medium, while evaluating the modulator time response to an arbitrary modulating signal. Small dielectric perturbations and a large difference between the optical and modulating signal frequencies are the only hypotheses used in deriving the linear model. By applying a multiple-scale perturbation method, we reach an analytical solution to the problem of multipolarization interaction. Some applications are discussed.     

Drain-induced barrier-lowering analysis in VSLI MOSFET devices using two-dimensional numerical simulations

In recent publications the drain-induced barrier-lowering (DIBL) effect has been included in the determination of the drain current of short-channel MOSFET's by way of analytical expressions. The validity of these published expressions has not been verified so far for small-geometry devices of different parameters. Further, the relationship between the threshold voltage shift and the barrier lowering due to the DIBL effect has not been clarified in the literature. In our present paper we carried a detailed study of the drain-induced barrier lowering in ion-implanted 1-µm VLSI MOSFET devices, leading to a better understanding and clarification of the fundamental mechanisms involved in the DIBL variation and its effect on the threshold voltage and subthreshold current. Further, we found that the calculated DIBL parameters of the analytical model reported in the literature do not agree with the numerically computed values. Hence we determined a set of new geometry parameters η andB/Afor the DIBL threshold relationship that can be used with the analytical model. Our work stresses the necessity of the use of two-dimensional numerical simulations when accurate evaluation of the DIBL effect in short-channel MOSFET's is required. Also, our results should be useful for calibrating existing analytical MOSFET models. In addition, our data and method could be used as a design tool for performance optimization of micrometer and submicrometer devices.     

Accurate current calculation in two-dimensional MOSFET models

Two-dimensional simulations of MOSFET's are widely used for the design of short-channel transistors used in VLSI circuits. These models use low order methods of discretization of solution variables. In this paper, a method of current calculation is presented which works with these methods and yields good accuracy. The method uses integration of the solution variables, rather than differentiation, and is similar to applying Ohm's law in two dimensions.     

Recent advances in two-dimensional photovoltaic devices

Two-dimensional (2D) materials have attracted tremendous interest in view of the outstanding optoelectronic properties, showing new possibilities for future photovoltaic devices toward high performance, high specific power and flexibility. In recent years, substantial works have focused on 2D photovoltaic devices, and great progress has been achieved. Here, we present the review of recent advances in 2D photovoltaic devices, focusing on 2D-material-based Schottky junctions, homojunctions, 2D−2D heterojunctions, 2D−3D heterojunctions, and bulk photovoltaic effect devices. Furthermore, advanced strategies for improving the photovoltaic performances are demonstrated in detail. Finally, conclusions and outlooks are delivered, providing a guideline for the further development of 2D photovoltaic devices.     

渐变截面多模干涉器件中MMI区长度的计算

从渐变截面波导与强导近似的阶跃截面波导之间的区别入手,推导出了渐变截面ＭＭＩ区长度的精确表达式,并对成像的振幅和相位关系进行了研究。结果表明,在相同ＭＭＩ区宽度条件下渐变截面器件中ＭＭＩ区最短长度为阶跃截面的两倍,但它的设计灵活性却是阶路截面器件所无法比拟的。     

Simulation study of Short-Channel Effects and quantum confinement in double-gate FinFET devices with high-mobility materials

We developed a quantum-mechanical simulation code to study subthreshold performances and carrier quantum confinement in double-gate MOSFETs with high-mobility channel materials like Ge and III-V semiconductors. The code is based on the two-dimensional and self-consistent numerical solving of Poisson and Schrödinger equations coupled with the drift-diffusion transport equation. We systematically evaluate and analyze drain-induced barrier lowering and carrier quantum confinement in Si, Ge, In_0.53Ga_0.47As and GaAs based double-gate devices. Results show that SCEs in In_0.53Ga_0.47As and GaAs devices are lower than in Si and Ge counterparts. However, when the channel film thickness is reduced, carrier confinement is found to strongly impact double-gate device operation with high-mobility materials owing to their low confinement effective mass in the lowest energy valley.     

Semiconductor three-dimensional and two-dimensional photoniccrystals and devices

Semiconductor three-dimensional (3-D) and two-dimensional (2-D) photonic crystals and their effects on the control of photons are investigated for possible applications to optical chip and functional devices. First we review our approaches creating full 3-D photonic bandgap crystals at near-infrared wavelengths, and also functional devices based on 2-D photonic crystals where the focus is on surface-emitting-type channel-drop filtering devices utilizing single defects in 2-D photonic crystal slabs. Then, we describe the recent progress on 3- and 2-D crystals. On 3-D crystals, the effect of the introduction of a light emitter into the 3-D photonic crystal is investigated, and the design of a single defect cavity is performed. On the 2-D photonic crystals, the photonic states are investigated from the perspective of their polarization properties     

Quantum confinement and charge control in deep mesa etched quantumwire devices

Novel aspects of charge confinement in quantum wires are investigated with a self-consistent Schrodinger-Poisson model in the high-temperature regime. A decreasing eigenenergy separation with gate bias is revealed which differs from the behavior observed in 2-D devices. In addition, charge control is examined and an analytical approximation relating charge density to gate bias is obtained     

Accurate analysis of two-dimensional electromagnetic scattering from multilayered periodic arrays of circular cylinders using lattice sums technique

A very efficient and accurate method to characterize two-dimensional (2-D) electromagnetic scattering from multilayered periodic arrays of parallel circular cylinders is presented, using the lattice sums technique, the aggregate T-matrix algorithm, and the generalized reflection and transmission matrices for a layered system. The method is quite general and applies to various configurations of 2-D periodic arrays. The unit cell of the array can contain two or more cylinders, which may be dielectric, conductor, gyrotropic medium, or their mixture with different sizes. The periodic spacing of cylinders along each array plane should be the same over all layers, but otherwise the cylinders in different layers may be different in material properties and dimensions. The numerical examples validate the usefulness and accuracy of the proposed method.     

Accurate algorithm for temperature calculation of devices in nonlinear-circuit-analysis programs

An exact method is given for the temperature determination of devices in circuits analysed by nonlinear-circuit-analysis programs. The method is based on the simultaneous solution of the electronic and thermal network equations by introducing the `thermal-node? temperatures as well as the node voltages. These voltages and temperatures are arranged in a joint state vector.     

On solving Poisson's equation in two-dimensional semiconductor devices

An iterative method is proposed for solving Poisson's linear equation in two-dimensional semiconductor devices which enables two-dimensional field problems to be analysed by means of the well known depletion region approximation. An example of its application to an FET structure is then presented.     

Accurate two-dimensional approach for capacitance calculation inmicrocoplanar MES transmission lines

A new two-dimensional approach is proposed for the analysis of microcoplanar metal-semiconductor structures, where the depletion layer capacitance is calculated accurately after an exact determination of its boundary. The Green function, which is used to invert the Laplacian operator, is obtained by means of a conformal mapping technique to take into account the real position of the ground planes. The method constitutes a solid base for a further study of slow-wave MES coplanar waveguides and, with a small change in the boundary conditions, it can be extended to the analysis of MESFET propagating structures     

Square ring laser diode with MMI coupler cavity

A square ring laser diode is designed and fabricated in which a multimode interference 3-dB coupler operates as an output coupler and a ring resonator simultaneously. This merged structure allows a shorter cavity length and a lower loss in the output branching. Lasing in the ring cavity is confirmed and the spectra are also measured.     

二维限制多模干涉器非对称自映像特性

采用导模传输法分析了二维限制多模干涉器 (MMI)的自映像效应 ,详细讨论了二维限制MMI器件的非对称自映像性质 ,并用三维全矢量光束传输法验证了分析结果