Physical modeling of an optical memory cell based on quantum dot-in-well hybrid structure

In this paper we present a physical modeling and simulation result of an optical memory cell based on a semiconductor quantum-dot in quantum-well hybrid structure. The physical modeling and simulation were done in Crosslight Apsys software which offers advanced models for photoelectric devices. We have optimized the scan conditions, iterative algorithm and other simulation parameters in order to obtain a solution. The calculated I–V and C–V curves agree with the experimental results and demonstrate that the cell can be used for photon storage.     

Some non-linear aspects of the electronic stages in time-domain modelling of NDE pulse-echo ultrasonic systems

Electronics interfacing with NDE probes frequently include non-linear switching devices and semiconductor networks, which influence the excitation pulses and detected echo signals. Classical approaches to modelling a pulse-echo process use ideal assumptions for the electronics and do not consider these influences on the echoes, which can be very relevant in HF cases. This paper proposes new ways to consider these non-linear effects in a time-domain simulation process, extending previous approaches by including new elements in the modelling. Specific electrical models covering the pulse-echo process are applied in the evaluation of echo-graphic signals. They include semiconductor devices and other non-ideal elements. From these models, and using SPICE as a simulation tool, strong non-linear effects on pulsed responses, computed for both E/R stages of typical NDE transceivers, are analysed.     

Coupling atomistic and finite element approaches for the simulation of optoelectronic devices

Multiscale methods coupling quantum mechanical/atomistic models such as envelope function and tight binding approaches with continuous media models e.g. for strain or electronic transport are very useful for an accurate simulation of modern and emerging electronic and optoelectronic devices based on nanostructured active regions. We present simulations using TiberCAD whose main focus is on providing an integrated multiscale/multiphysics simulation environment.     

Semiconductor processing

The impact of ion implantation on present day semiconductor device processing and future applications to simplify and improve processing are described.

So far implantation has generally been used to introduce electrically active dopants into the semiconductor but it can also be used to improve other stages of the technology of making semiconductor devices. Ion implantation can be used to improve masks, etching, step coverage, and slice distortion and such applications are reviewed.

The many processes involved in making semiconductor devices interact in a complex way. Apparently small changes, such as replacing depositions by implantation, can lead to unsatisfactory device properties unless significant changes are made in subsequent processing. The complex interactions make the design of new processes critical if optimum properties are to be achieved. Special constraints can be placed on the implantation process itself. Examples are given of these interactions.     

Numerical analysis of steady-state and transient charge transport in organic semiconductor devices

A one-dimensional numerical model for the simulation of organic semiconductor devices such as organic light-emitting devices and solar cells is presented. The model accounts for the energetic disorder in organic semiconductors and assumes that charge transport takes place by a hopping process between uncorrelated sites. Therefore a Gaussian density of states and the use of the Fermi-Dirac statistics are introduced. The model includes density-, field- and temperature- dependent mobilities as well as the generalized Einstein relation. The numerical methods to solve the underlying drift-diffusion problem perform well in combination with the novel physical model ingredients. We demonstrate efficient numerical techniques that we employ to simulate common experimental characterization techniques such as current-voltage, dark-injection transient and electrical impedance measurements. This is crucial for physical model validation and for material parameter extraction. We also highlight how the numerical solution of the novel model differs from the analytical solution of the simplified drift-only model.     

Quantum mechanical Monte Carlo approach to electron transport at heterointerface

With the progress of LSI technology, the electronic device size is scaled down to the sub 0.1μ m region. In such an ultrasmall device, it is indispensable to take quantum mechanical effects into account in device modeling. In this paper, we present a newly developed quantum Monte Carlo device simulation applicable to ultrasmall semiconductor devices. In this model, the quantum effects are represented in terms of quantum mechanically corrected potential in the classical Boltzmann equation. It is demonstrated that the quantum transport effects such as tunneling and energy quantization in ultrasmall semiconductor devices are obtained for the first time by using the standard Monte Carlo techniques.     

Recent applications of Monte Carlo methods for semiconductor microdevice simulation

Monte Carlo simulations for semiconductor devices are very time consuming. We have investigated ways to speed up calculations on supercomputers and a method to incorporate overshoot effects in simple drift-diffusion models for submicron devices, using coefficients obtained from Monte Carlo experiments. An Ensemble Monte Carlo algorithm, suitable for self-consistent device simulation, has been vectorized, and in preliminary runs three times faster on a CRAY X/MP 48 supercomputer. The inclusion of overshoot terms in a drift-diffusion simulation for a MESFET structure, shows that the main overshoot effects can be incorporated in a simple model suitable for circuit simulation. Increased problems in stability, however, reduce the efficiency of traditional finite difference schemes and require further refinement in the numerical methods.     

Single quantum dot nanolaser

Recent theoretical and experimental progress on nanolasers is reviewed with a focus on the emission properties of devices operating with a few or even an individual semiconductor quantum dot as a gain medium. Concepts underlying the design and operation of these devices, microscopic models describing light‐matter interaction and semiconductor effects, as well as recent experimental results and lasing signatures are discussed. In particular, a critical review of the “self‐tuned gain” mechanism which gives rise to quantum‐dot mode coupling in the off‐resonant case is provided. Furthermore recent advances in the modeling of single quantum dot lasers beyond the artificial atom model are presented with a focus on the exploration of similarities and differences between the atomic and semiconductor systems.     

Ion implantation for semiconductor processing

The potential advantages of ion implantation have been exploited in virtually every kind of semiconductor device. Several commercially important devices owe their existence to this technique.

Ion implantation provides precise control over the amount of dopant, concentration profile and lateral dimensions in device fabrication. The high degree of uniformity and reproducibility have made it possible to produce sophisticated devices and integrated circuits with high yield and tight tolerances. This is a truly planar process. It is possible to achieve high doping concentrations with relatively lower processing temperatures thereby avoiding lifetime degradation. The process is carried out in an inherently clean environment. A wide range of dopants is available and one is not limited by the particular properties of the substrate. There is great flexibility in choice of masking materials and self-alignment of doped regions in MOS devices is facilitated.

The increasing impact of ion implantation on device technology is discussed with reference to some recent developments. Specific commercially manufactured devices are mentioned.

Ion implantation machines continue to undergo development aimed at higher throughputs and cleaner vacuum. There is the need for greater reliability of machines. Effort is also directed at the development of low cost machines for dedicated applications.

Design of implanted devices continues to be an empirical process in some respects. The ability to accurately predict profile shapes in samples implanted (perhaps through a screen oxide) and subject to complicated post-implantation process steps, would cut down development time and costs.     

Femtosecond hybrid mode-locked semiconductor laser and amplifier dynamics

We describe the generation of femtosecond high power optical pulses using hybrid passive-active mode-locking techniques. Angle stripe geometry GaAs/AlGaAs semiconductor laser amplifiers are employed in an external cavity including prisms and a stagger-tuned quantum-well saturable absorber. An identical amplifier also serves as an optical power amplifier in a stretched pulse amplification and recompression sequence. After amplification and pulse compression this laser system produces 200 fs, 160 W peak power pulses. We discuss and extend our theory, and supporting phenomenological models, of picosecond and subpicosecond optical pulse amplification in semiconductor laser amplifiers which has been successful in calculating measured spectra and time-resolved dynamics in our amplifiers. We have refined the theory to include a phenomenological model of spectral hole-burning for finite intraband thermalization time. Our calculations are consistent with an intra-band time of approximately 60 fs. This theory of large signal subpicosecond pulse amplification will be an essential tool for understanding the mode-locking dynamics of semiconductor lasers and for analysis of high speed multiple wave-length optical signal processing and transmission devices and systems based on semiconductor laser amplifiers.     

Investigation of the transport mechanism in graphene-induced metal-oxide-semiconductor capacitors (MOSCAP)

Graphene is the most promising contender for the future generation of electronic and photonic devices, based on its extraordinary properties. The effect of the metal interface with graphene, however, which completely alters its properties, is of great importance. The effects of the substrate supporting the graphene matrix, the graphene/metal contact resistance and the overall metal oxide semiconductor capacitors (MOSCAP) for possible CMOS circuitry have been thoroughly investigated in this research work. We have fabricated a structure with pertinent deposition techniques and performed a detailed electrical analysis to obtain the transport characteristics. Nickel (Ni) is chosen as the transition metal which makes the chemisorption bonding with graphene while qualifying as an interface. We present an analysis of the metal contacts, a study of the metal resistivity at various planes, a study of the graphene (carbon) atom's resistance at the atomistic scale, the graphene based MOSCAP leakages, the necessary charge accumulation at the metal–graphene interface and the charge inversion just beneath the oxide layer.     

Physical device models: A potential tool in investigating conductivity in ionic and mixed conductors

Extensive work has been done in the last three decades on modelling classical semiconductor devices through physical device models. The majority of these models is based on the simultaneous solution of Poisson's equation, current and continuity equations for electrons and holes using iterative techniques. The vast work done on classical semiconductor devices has been extended to include the study of the motion of charged species upon the application of external fields in insulators, ionic materials, mixed conductors or proton conductors. In this paper the methods used are discussed together with their potential in leading to an understanding of the mechanisms governing charge transport in materials exhibiting more complex conductivity than classical semiconductors. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Top down nano technologies in surface modification of materials

This article contains a broad overview of etch process as one of the most important top-down technologies widely used in semiconductor manufacturing and surface modification of nanostructures. In plasma etching process, the complexity comes from the introduction of new materials and from the constant reduction in dimensions of the structures in microelectronics. The emphasis was made on two types of etching processes: dry etching and wet etching illustrated by three dimensional (3D) simulation results for the etching profile evolution based on the level set method. The etching of low-k dielectrics has been demonstrated via modelling the porous materials. Finally, simulation results for the roughness formation during isotropic etching of nanocomposite materials as well as smoothing of the homogeneous materials have also been shown and analyzed. Simulation results, presented here, indicate that with shrinking microelectronic devices, plasma and wet etching interpretative and predictive modeling and simulation have become increasingly more attractive as a tool for design, control and optimization of plasma reactors.     

单管体硅,SOI及DSOI MOSFET热分析

本文简单介绍了SOI和 DSOI半导体器件制造技术,并提出了单管体硅,SOI及 DSOI MOSFET的热阻模型。进而对体硅,SOI MOSFET器件,特别是DSOI MOSPET的热学特性进行数值计算,比较并分析了其数值计算结果。     

Physically based model for trapping and self-heating effects in 4H-SiC MESFETs

In order to accurately and simply extract the trapping parameters in SiC metal semiconductor field effect transistors (MESFETs) a method is proposed based on device dc and ac small-signal models. By combining modeling techniques, material physics, and measured device characteristics, we are able to estimate the important information about the trap property and heat flow in 4H-SiC material and their influences on performance of MESFET devices, including gate lag, frequency-related dispersion, and the self-heating effect. Simulations indicate that the gate lag is due to the traps located at the channel/buffer interface and the transition frequency is up to ∼ MHz at 600 K. PACS 72.15.Jf; 72.20.Jv; 72.15.Eb     

SPICE modeling of flux-controlled unipolar memristive devices

Unipolar memristive devices are an important kind of resistive switching devices. However, few circuit models of them have been proposed. In this paper, we propose the SPICE modeling of flux-controlled unipolar memristive devices based on the memristance versus state map. Using our model, the flux thresholds, ON and OFF resistance, and compliance current can easily be set as model parameters. We simulate the model in HSPICE using model parameters abstracted from real devices, and the simulation results show that the proposed model caters to the real device data very well, thus demonstrating that the model is correct. Using the same modeling methodology, the SPICE model of charge-controlled unipolar memristive devices could also be developed. The proposed model could be used to model resistive memory cells, logical gates as well as synapses in artificial neural networks.     

半导体器件多物理场计算中的热边界条件北大核心CSCD

基于半导体器件的物理模型,联立并求解由电磁场、半导体物理及热力学方程构成的多物理场方程组,实现半导体器件及电路的电磁效应计算。为了更加准确地仿真半导体器件的温度变化,深入研究了多物理场计算中的热边界条件。以肖特基二极管HSMS-282c为例,采用多物理场算法仿真并对比了器件在相同激励(幅值为2V的阶跃脉冲)、不同边界条件下的温度变化情况。实际测量了器件在正向偏置下的表面温度,并于多物理场计算结果进行对比。结果表明,采用热对流边界可以准确仿真半导体器件的热效应。