Increase in the random dopant induced threshold fluctuations andlowering in sub-100 nm MOSFETs due to quantum effects: a 3-Ddensity-gradient simulation study

In this paper, we present a detailed simulation study of the influence of quantum mechanical effects in the inversion layer on random dopant induced threshold voltage fluctuations and lowering in sub-100 mn MOSFETs. The simulations have been performed using a three-dimensional (3-D) implementation of the density gradient (DG) formalism incorporated in our established 3-D atomistic simulation approach. This results in a self-consistent 3-D quantum mechanical picture, which implies not only the vertical inversion layer quantization but also the lateral confinement effects related to current filamentation in the “valleys” of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical dopant fluctuations, is an increase in both threshold voltage fluctuations and lowering. At the same time, the random dopant induced threshold voltage lowering partially compensates for the quantum mechanical threshold voltage shift in aggressively scaled MOSFETs with ultrathin gate oxides     

A comparative study of NEGF and DDMS models in the GAA silicon nanowire transistor

In this article, we have used quantum and semiclassical models to analyse the electrical characteristics of gate all around silicon nanowire transistor (GAA SNWT). A quantum mechanical transport approach based on non-equilibrium Green's function (NEGF) method with the use of mode space approach in the frame work of effective mass theory has been employed for this analysis. Semiclassical drift diffusion mode space (DDMS) approach has also been used for the simulation of GAA SNWT. We have studied the short-channel effects on the performance of GAA SNWT and evaluated the variation of the threshold voltage, the subthreshold slope (SS), the leakage current and the drain-induced barrier lowering (DIBL) when channel length gets shorter. The results showed that quantum mechanical effects increase the threshold voltage and decrease the leakage current, whereas it has also an impact on the SS and DIBL. We have also investigated the effects of high-κ materials as gate dielectric on the device performance.     

Experimental evidence for quantum mechanical narrow channel effectin ultra-narrow MOSFET's

The authors describe a new narrow channel effect by quantum mechanical effects in ultra-narrow MOSFET's. Threshold voltage increase is observed at room temperature in ultra-narrow MOSFET's whose channel width is less than 10 nm. This result is in excellent agreement with simulation that takes account of quantum confinement in the silicon narrow channel, indicating that the increase in threshold voltage is caused by the quantum mechanical narrow channel effect     

基于密度梯度理论的MOS量子隧穿解析模型

提出了一种基于物理的MOS电容超薄氧化层量子隧穿解析模型,量子力学效应在应用奇异微扰法求解密度梯度方程时得以体现.将泊松方程和经量子修正的电子势方程同时求解,得出电子和静电势在垂直于沟道方向的分布.结果反映出量子效应明显不同于经典物理学的预测.对解析解结果和精确的数值模拟进行比较,结果表明,在栅极偏压和氧化层厚度的较大变化范围内,二者都能很好地吻合.     

Random dopant induced threshold voltage lowering and fluctuationsin sub-0.1 μm MOSFET's: A 3-D “atomistic” simulationstudy

A three-dimensional (3-D) “atomistic” simulation study of random dopant induced threshold voltage lowering and fluctuations in sub-0.1 μm MOSFETs is presented. For the first time a systematic analysis of random dopant effects down to an individual dopant level was carried out in 3-D on a scale sufficient to provide quantitative statistical predictions. Efficient algorithms based on a single multigrid solution of the Poisson equation followed by the solution of a simplified current continuity equation are used in the simulations. The effects of various MOSFET design parameters, including the channel length and width, oxide thickness and channel doping, on the threshold voltage lowering and fluctuations are studied using typical samples of 200 atomistically different MOSFETs. The atomistic results for the threshold voltage fluctuations were compared with two analytical models based on dopant number fluctuations. Although the analytical models predict the general trends in the threshold voltage fluctuations, they fail to describe quantitatively the magnitude of the fluctuations. The distribution of the atomistically calculated threshold voltage and its correlation with the number of dopants in the channel of the MOSFETs was analyzed based on a sample of 2500 microscopically different devices. The detailed analysis shows that the threshold voltage fluctuations are determined not only by the fluctuation in the dopant number, but also in the dopant position     

Sensitivity of double-gate and FinFETDevices to process variations

We investigate the manufacturability of 20-nm double-gate and FinFET devices in integrated circuits by projecting process tolerances. Two important factors affecting the sensitivity of device electrical parameters to physical variations were quantitatively considered. The quantum effect was computed using the density gradient method and the sensitivity of threshold voltage to random dopant fluctuation was studied by Monte Carlo simulation. Our results show the 3/spl sigma/ value of V/sub T/ variation caused by discrete impurity fluctuation can be greater than 100%. Thus, engineering the work function of gate materials and maintaining a nearly intrinsic channel is more desirable. Based on a design with an intrinsic channel and ideal gate work function, we analyzed the sensitivity of device electrical parameters to several important physical fluctuations such as the variations in gate length, body thickness, and gate dielectric thickness. We found that quantum effects have great impact on the performance of devices. As a result, the device electrical behavior is sensitive to small variations of body thickness. The effect dominates over the effects produced by other physical fluctuations. To achieve a relative variation of electrical parameters comparable to present practice in industry, we face a challenge of fin width control (less than /spl sim/1 nm 3/spl sigma/ value of variation) for the 20-nm FinFET devices. The constraint of the gate length variation is about 10/spl sim/15%. We estimate a tolerance of 1/spl sim/2 /spl Aring/ 3/spl sigma/ value of oxide thickness variation and up to 30% front-back oxide thickness mismatch.     

Macroscopic simulation of quantum mechanical effects in 2-D MOSdevices via the density gradient method

Here, for the first time, are presented results of two-dimensional (2-D) simulations of metal-oxide-semiconductor (MOS) devices, including quantum mechanical modeling throughout the entire device region, calculated using the density gradient method. The importance of quantum mechanical modeling of the entire device structure, including the gate, source, drain, and channel, is demonstrated through one-dimensional (1-D) examples and through analysis of double and single-gated fully-depleted silicon-on-insulator (SOI) devices. A comparison of density gradient results with literature data is also presented     

Effect of strain on CHSH Auger recombination in strainedIn0.53+xGa0.47-xAs on InP

We calculate the |conduction, heavy hole〉- |split-off hole, heavy hole〉 (CHSH) Auger rates in strained In_0.53+xGa _0.47-xAs on InP, a widely used material system for quantum well lasers. The bandstructure is obtained from an eight-band tight binding model with spin-orbit coupling, strain effects being included via the deformation potential theory. Adding excess In decreases the hole density of states: this effect acts to decrease the Auger rates. The excess In also decreases the bandgap, however, and increases the split-off gap: these effects act to increase the Auger rates. When we include both of these effects we find that the reduction in the net bandgap dominates; hence, the Auger rates increase with excess In for a fixed carrier concentration. We include these Anger rates in the threshold current calculation for a strained layer multi quantum well laser. We find that for x<0.15 the strain-induced reduction in the threshold carrier concentration is able to offset the higher Auger rates; thus, the threshold current decreases rapidly with x. For x>0.15, however, the threshold carrier concentration changes little and the Anger rates continue to increase; thus, the threshold current begins to increase rapidly with x     

考虑量子效应的双栅MOSFET的阈电压解析建模

推导了双栅MOSFET器件在深度方向上薛定谔方程的解析解以求得电子密度和阈电压.该解析解考虑了任意深度情况下沟道中深度方向上电势的不均匀分布,结果与数值模拟吻合.给出了电子密度的隐式表达式和阈电压的显式表达式,它们都充分考虑了量子力学效应.模型显示,在亚阈值区或者弱反型区,电子密度随深度增加而增加;然而,在强反型区,它与深度无关,这与数值模拟的结果吻合.结果进一步显示,只考虑方形势阱的量子力学结果,略高估计了阈电压,且低估了电子密度.误差随着深度的增加或者栅氧厚度的减少而增加.     

耦合波导结构量子阱激光器的理论设计与分析

报道了一种具有垂直集成无源波导的耦合波导结构量子阱激光器的理论设计，它可以使垂直结平面方向的远场光束发散角得到有效的降低。通过数值计算分析，详细研究了结构参数对远场及阈值电流密度等的影响。结果表明，只需增加较小的阈值电流密度，即可使远场光束得到较大改善。经优化设计，可获得发散角为２１°的９８０ｎｍＩｎＧａＡｓ／ＡｌＧａＡｓ量子阱激光器结构。     

量子线和量子箱激光器—下一代高性能半导体激光器

本文讨论了量子线和量子箱激光器的特性,如呈现非常低的阈值电流、展宽的调制带宽和窄的谱线宽度。还介绍了量子尺寸结构的制造工艺、尺寸起伏和非线性增益对激射特性的影响。最后给出量子微腔激光器的新概念。     

两种激光模型的量子起伏

本文研究激光理论中使用的两种模型（Ｈａｋｅｎ模型和Ｌｏｕｉｓｅｌｌ模型）的量子起伏，在Ｈａｋｅｎ模型中，激光介质由两能级原子组成，而Ｌｏｕｉｓｅｌｌ模型中是由三能级电子组成，在原了量绝热消除条件下，研究两种模型在阈值附近或远高于阈值时，输出光谱的振由幅起伏。     

Localized Auger Recombination in Quantum-Dot Lasers

We have calculated radiative and Auger recombination rates due to localized recombination in individual dots, for an ensemble of 10⁶ dots with carriers occupying the inhomogeneous distribution of energy states according to global Fermi-Dirac statistics. The recombination rates cannot be represented by simple power laws, though the Auger rate has a stronger dependence on the ensemble electron population than radiative recombination. Using single-dot recombination probabilities which are independent of temperature, the ensemble recombination rates and modal gain decrease with increasing temperature at fixed population. The net effect is that the threshold current density increases with increasing temperature due to the increase in threshold carrier density. The most significant consequence of these effects is that the temperature dependence of the Auger recombination rate at threshold is much weaker than in quantum wells, being characterized by a T₀ value of about 325 K. Observations of a strong temperature dependence of threshold in quantum dot lasers may have explanations other than Auger recombination, such as recombination from higher lying states, or carrier leakage.     

Analysis of high-frequency response and nonlinear coherent generation of resonance-tunneling diodes within a broad frequency range with account of electron-electron interaction

The response and power of the coherent generation of a resonance-tunneling diode have been calculated numerically taking into account the electron-electron interaction within a broad frequency range within the framework of a consistent quantum mechanical model. The “quantum” generation mode is shown to persist even in the presence of electron-electron interaction. Thus, a high-power generation at frequencies exceeding the resonance level width is possible. One can even expect an improvement of the generation parameters in the “classical” mode, in particular, the lowering of the generation threshold. This results from a rise in the negative differential conductance due to electron-electron interaction.     

Compact Threshold Voltage Model for FinFETs

A 2D analytical electrostatics analysis for the cross-section of a FinFET (or tri-gate MOSFET) is performed to calculate the threshold voltage.The analysis results in a modified gate capacitance with a coefficient Ｈ introduced to model the effect of trigates and its asymptotic behavior in 2D is that for double-gate MOSFET.The potential profile obtained analytically at the cross-section agrees well with numerical simulations.A compact threshold voltage model for FinFET,comprising quantum mechanical effects,is then proposed.It is concluded that both gate capacitance and threshold voltage will increase with a decreased height,or a decreased gate-oxide thickness of the top gate，which is a trend in FinFET design.     

An accurate two-dimensional CAD-oriented model of retrograde doped MOSFETs for improved short channel performance

An analytical CAD-oriented model for short channel threshold voltage of retrograde doped MOSFETs is developed. The model is extended to evaluate the drain induced barrier lowering parameter (R) and gradient of threshold voltage. The dependence of short channel threshold voltage and R on thickness of lightly doped layer (d) has also been analyzed in detail. It is shown that a retrograde doping profile reduces short channel effects to a considerable extent. A technique is developed to optimize the device parameters for minimizing short channel effects. The results so obtained are in close proximity with published data.     

Theoretical studies of GaInP-AlGaInP strained quantum-well lasersincluding spin-orbit split-off band effect

We studied the GaInP-AlGaInP strained quantum-well laser characteristics, taking into account the spin-orbit split-off bands. When the well width is kept constant at 85 Å, the threshold current of the unstrained quantum-well structure is most degraded by the effect of the spin orbit split-off subbands, due to the larger hole density of states near the band-edge. While the linear gain of the compressive-strained quantum well is slightly changed by the effect, it has the lowest threshold current with the lower threshold gain. In the tensile-strained quantum-well structure, the spin-orbit split-off bands improve the differential gain because they increase the density of states at the valence band-edge. When the lasing wavelength is fixed at 630 nm, the threshold current of the compressive-strained quantum well is the lowest as well. The tensile-strained quantum well has lower threshold current than the unstrained quantum well, and this phenomena is not observed in the analysis without the spin-orbit split-off bands. However, the reduction of threshold current of the tensile-strained quantum well is smaller than that of compressive-strained quantum well, The tensile strain is more preferable for high speed modulation because of its large differential gain, due to the mixing between the light hole and the spin-orbit split-off subbands     

GCS法及多晶区量子效应的集约建模

提出了一种新的建立集约模型的方法,即栅电容修正法.此方法考虑了新型效应对栅电压的依赖关系,且可以对各种效应相对独立地建模并分别嵌入模型中.另外,利用该方法和密度梯度模型建立了一个多晶区内量子效应的集约模型.该模型与数值模拟结果吻合.模型结果和模拟结果均表明,多晶区内的量子效应不可忽略,且它对器件特性的影响与多晶耗尽效应相反.     

GCS法及多晶区量子效应的集约建模

提出了一种新的建立集约模型的方法,即栅电容修正法.此方法考虑了新型效应对栅电压的依赖关系,且可以对各种效应相对独立地建模并分别嵌入模型中.另外,利用该方法和密度梯度模型建立了一个多晶区内量子效应的集约模型.该模型与数值模拟结果吻合.模型结果和模拟结果均表明,多晶区内的量子效应不可忽略,且它对器件特性的影响与多晶耗尽效应相反.     

Intrinsic threshold voltage fluctuations in decanano MOSFETs due tolocal oxide thickness variations

Intrinsic threshold voltage fluctuations introduced by local oxide thickness variations (OTVs) in deep submicrometer (decanano) MOSFETs are studied using three-dimensional (3-D) numerical simulations on a statistical scale. Quantum mechanical effects are included in the simulations employing the density gradient (DG) formalism. The random Si/SiO₂ and gate/SiO₂ interfaces are generated from a power spectrum corresponding to the autocorrelation function of the interface roughness. The impact on the intrinsic threshold voltage fluctuations of both the parameters used to reconstruct the random interface and the MOSFET design parameters are studied using carefully designed simulation experiments. The simulations show that intrinsic threshold voltage fluctuations induced by local OTV become significant when the dimensions of the devices become comparable to the correlation length of the interface. In MOSFETs with characteristic dimensions below 30 nm and conventional architecture, they are comparable to the threshold voltage fluctuations introduced by random discrete dopants