对称三材料双栅应变硅金属氧化物半导体场效应晶体管二维解析模型

提出了对称三材料双栅应变硅金属氧化物半导体场效应晶体管器件结构,为该器件结构建立了全耗尽条件下的表面势模型、表面场强和阈值电压解析模型,并分析了应变对表面势、表面场强和阈值电压的影响,讨论了三栅长度比率对阈值电压和漏致势垒降低效应的影响,对该结构器件与单材料双栅结构器件的性能进行了对比研究.结果表明,该结构能进一步提高载流子的输运速率,更好地抑制漏致势垒降低效应.适当优化三材料栅的栅长比率,可以增强器件对短沟道效应和漏致势垒降低效应的抑制能力.     

自旋场效应晶体管中隧道磁阻的势垒相关反转效应

考虑自旋场效应晶体管中Rashba自旋轨道相互作用和自旋输运量子相干性,研究了势垒强度对自旋场效应晶体管的自旋相关量子输运的影响. 研究发现,势垒强度较低时,隧道结电导随Rashba自旋轨道相互作用强度的变化呈现明显的振荡现象,势垒强度较高时,电导表现出明显的势垒相关“电导开关”现象. 当势垒强度逐渐增强时,平行结构电导呈现出单调下降趋势,而反平行结构电导产生波动,这种波动导致该隧道磁阻也随势垒强度的变化表现出振荡现象,且在合适的准一维电子气厚度情况下隧道磁阻值可以产生正负反转,这个效应将会在基于自旋的电子器件信息的存储上获得应用. 关键词： 自旋场效应管 开关效应 量子相干 隧道磁阻     

界面势垒对碳纳米管场发射特性的影响

以界面势垒对碳纳米管(CNT)场发射的影响为研究目的,在硅衬底上引进很薄的二氧化硅层,以二氧化硅层作为绝缘势垒,然后在二氧化硅界面层上直接生长CNT,来研究二氧化硅绝缘势垒层对CNT场发射的影响。场发射结果为:Fowler-Nordheim(F-N)曲线分为两部分,高电场下偏离F-N曲线并趋于饱和。在双势垒模型的基础上,从电场在两势垒上的分布不同及电子在两势垒上的隧穿几率不同,理论上分析了界面势垒对场发射的影响:低电场下电子在界面势垒的隧穿几率大于在表面势垒的隧穿几率,界面势垒对场发射不起阻碍作用,场发射遵守F-N规律;高电场下电子在界面势垒的隧穿几率小于在表面势垒的隧穿几率,场发射偏离F-N规律。理论对实验结果进行了合理的解释。     

外加轴向磁场下碳纳米管场效应晶体管的电学性质

在紧束缚理论的基础上推导出轴向磁场下碳纳米管的能带公式,研究外加磁场下碳纳米管场效应晶体管的电学特性.说明磁场可使碳管的导电性质在金属型和半导体型之间转变,转变的磁场周期为0.5₀.进一步应用场效应晶体管Natori理论模拟计算了外加磁场对碳纳米管场效应晶体管的电流-电压特性的影响,研究结果显示zigzag管和armchair管的电流随外电压和磁场都有振荡行为,而且两类管的振荡行为有明显差别. 关键词： 碳纳米管 紧束缚理论 费米能 能带结构     

表面势垒对梯度掺杂GaN光电阴极电子逸出几率的影响

研究表面势垒对梯度掺杂GaN光电阴极电子逸出几率的影响.计算梯度掺杂透射式GaN光电阴极的电子能量分布及逸出几率,结果显示梯度掺杂与均匀掺杂相比,可以获得更大的电子逸出几率;I势垒对电子逸出几率的影响显著,而Ⅱ势垒影响较小.利用GaN光电阴极多信息量测试系统,测试两种GaN阴极样品的光电流.实验结果表明,梯度掺杂GaN样品比均匀掺杂电子逸出几率更大;单独进行Cs激活形成的I势垒对电子逸出几率有显著影响,而Cs/O共同激活形成的Ⅱ势垒对其影响较小.     

非金属元素掺杂二硒化钨/石墨烯异质结对其肖特基调控的理论研究

采用平面波超软赝势方法研究了非金属元素掺杂对二硒化钨/石墨烯肖特基电子特性的影响.研究表明二硒化钨与石墨烯层间以范德瓦耳斯力结合形成稳定的结构.能带结果表明二硒化钨与石墨烯在稳定层间距下形成n型肖特基势垒.三维电子密度差分图表明石墨烯中的电子向二硒化钨移动,使二硒化钨表面带负电,石墨烯表面带正电,界面形成内建电场.分析表明,将非金属原子掺杂二硒化钨可以有效地调控二硒化钨/石墨烯肖特基势垒的类型和高度. C, O原子掺杂二硒化钨时,肖特基类型由p型转化为n型,并有效降低了肖特基势垒的高度; N, B原子掺杂二硒化钨时,掺杂二硒化钨体系表现出金属性,与石墨烯接触表现为欧姆接触.本文结果可为二维场效应晶体管的设计与制作提供相关指导.     

Ni/4H-SiC 肖特基势垒磁场下输运性质的分析

采用高真空电子束蒸发的方法将镍 (Ni)淀积在 4H SiC(0 0 0 1)面上 ,制备出良好的Ni/4H SiC肖特基接触 .研究了Ni/4H SiC肖特基势垒在强磁场和低温下的I -V特性 ,并以热电子发射理论为基础 ,结合弛豫近似玻尔兹曼方程对Ni/4H SiC肖特基势垒在磁场下的输运性质进行了分析和计算 ,发现电流的变化与磁场的平方和电压成线性关系 ,和温度成反比关系 ,与实验结果基本符合     

GaAs光电阴极表面电子逸出概率与波长关系的研究

GaAs光电阴极量子效率公式中用到的表面电子逸出概率,在阴极工作波段范围内通常视为与入射光子波长无关的常数。应用该结论对反射式GaAs光电阴极激活实验结果进行了拟合分析。实验采用分子束外延GaAs材料,外延发射层厚度为1.6μm、掺杂浓度为1×1019cm-3,分析结果显示理论曲线与实验曲线存在偏差,而在激活台内阴极灵敏度下降后的光谱响应曲线拟合结果偏差更大。这种偏差是由于表面电子逸出概率对入射光子波长的依赖关系造成的,并非通常认为的与波长无关。经过光谱响应曲线的拟合分析得出,反射式阴极表面电子逸出概率与入射光子波长之间近似满足指数关系,两者通过表面势垒因子相联系。高、低温激活后阴极表面势垒因子分别为3.53和1.36。     

Bi2212体系的层间耦合对临界电流密度的影响

通过对具有不同层间耦合强度的Bi2212单晶样品的磁滞回线的测量,得到了样品的临界电流密度Jc随层间耦合强度和磁场的变化关系．实验结果显示,样品的层间耦合减弱,Jc明显减小．同时发现Jc与磁场间存在Jc ∝ exp(-H^a)关系,进一步分析表明,Jc的这种磁场依赖关系是对数钉扎势垒模型的必然结果．     

成型压力对CrO2低温输运性质的影响

本文研究了压力对CrO₂样品低温磁输运性质的影响.样品的X射线衍射结果表明(110)峰的相对强度随压力的增加而增大，说明压力对CrO₂针状纳米颗粒有取向的作用.低温时CrO₂样品的电阻和磁阻均随压力的增加而减少.实验结果表明，低温下样品的电导呈现出典型的晶粒间隧穿特征，其Δ值随着压力和磁场的增加而减小，并且Δ随磁场的变化幅度与成型压力有关，成型压力越高，Δ随磁场的变化越小.这些变化可以归因为压力对晶粒间隧穿势垒的调制. 关键词： 磁阻 压力 隧穿 势垒厚度     

栅极电势对强光场下石墨烯场效应管中电子隧穿的影响

利用时域有限差分方法研究了强光场下石墨烯场效应管中栅极电势对电子隧穿的影响. 在强光场下由于光学stark效应,石墨烯场效应管的完美手征透射被抑制.这种抑制除了 可以利用光场来调控外,也可以通过改变栅极电势的宽度、势垒高度等来调控. 研究了非方势垒中电子的隧穿. 研究发现,当电势的倾斜较小时,电子隧穿概率变化不大.而当电势倾斜很大时,电子隧穿概率急剧改变.     

Spectral photoresistive effect of the field in CdS crystals at low temperatures

The influence of the surface electric field on the low-temperature (T=77 K) photoconductivity spectra of CdS crystals in the region of exciton and interband transitions is experimentally studied by the field-effect method. The photoconductivity spectra of a semiconductor are numerically calculated in the framework of a model allowing for the dependence of the surface recombination rate of nonequilibrium charge carriers on the surface electric field. It is demonstrated that the surface electric field plays a decisive role in the formation of the fine spectral structure associated with the excitons. A correlation between the type of fine structure and the surface bending of the energy bands is revealed. It is shown that the surface electric field can be evaluated from the shape of the low-temperature photoconductivity spectrum of the semiconductor.     

Probing the spin state of a single electron trap by random telegraph signal

We have studied the random telegraph signal (RTS) generated by a single paramagnetic spin center adjacent to a submicrometer silicon metal-oxide-semiconductor field-effect transistor. An in-plane magnetic field induces a substantial change in the statistics of the RTS. We show that a model using the grand partition theorem can qualitatively explain the change in statistics of the RTS as a function of the applied magnetic field. While the data at high temperatures can be well described by this simple model, quantitative discrepancy increases as the temperature is lowered.     

Surface impedance of a superconducting slab in the mixed state: Effect of the surface barrier

The effect of the surface barrier on the surface impedance Z of a type-II superconductor slab with a finite thickness is investigated in dc magnetic fields H ₀, which are aligned parallel or perpendicular to the slab plane. It is demonstrated that, in a perpendicular geometry, the surface resistivity ρ_s=ReZ has a maximum when the depth of penetration of the ac magnetic field is of the order of the slab thickness (size effect). For a parallel orientation of the magnetic field H ₀, the effect of the Bean-Livingston surface barrier manifests itself as a decrease in the dissipative loss and a change in the field dependence of the surface resistivity characterized by a magnetic hysteresis. It is shown for the first time that, under the conditions of persistent trapped magnetic flux, the dependence ρ_s(H ₀) is a decreasing function, which is associated, in particular, with a nontrivial suppression of the size effect.     

Two-step flux penetration in classic antiferromagnetic superconductor

The influence of antiferromagnetic order on the mixed state of a superconductor may result in creation of spin-flop domains along vortices. This may happen when an external magnetic field is strong enough to flip over magnetic moments in the vortex core from their ground state configuration. The formation of domain structure causes modification of the surface energy barrier, and creation of the new state in which magnetic flux density is independent of the applied field. The modified surface energy barrier has been calculated for parameters of the antiferromagnetic superconductor DyMo₆S₈. The prediction of two-step flux penetration process has been verified by precise magnetization measurements performed on the single crystal of DyMo₆S₈ at milikelvin temperatures. A characteristic plateau on the virgin curve B(H ₀) has been found and attributed to the modified surface energy barrier. The end of the plateau determines the critical field, which we call the second critical field for flux penetration. Received 16 August 2002 / Received in final form 22 October 2002 Published online 29 November 2002     

黏性、表面张力和磁场对Rayleigh-Taylor不稳定性气泡演化影响的理论分析

采用理论分析的方法考察了磁场中非理想流体中Rayleigh-Taylor(RT)不稳定性气泡的演化过程,在与磁场垂直的平面中,综合考虑流体黏性和表面张力的影响,推导了二维非理想磁流体RT不稳定性气泡运动的控制方程组,给出了不同情况下气泡速度的渐近解和数值解,分析了流体黏性、表面张力和磁场对气泡发展的影响,分析结果表明:流体黏性和表面张力能够降低气泡速度和振幅,即能够抑制RT不稳定性;而磁场对RT不稳定性的影响是由非线性部分引起的,并且磁场非线性部分的方向决定了磁场是促进还是抑制RT不稳定性的发展,     

Surface versus bulk pinning in a HgBa2Ca2Cu3O8+x ceramics

Flux creep measurements on a HgBa₂Ca₂Cu₃O_8+x ceramics are reported. The results of the magnetic relaxation measurements are analyzed both by assuming that the pinning is due to the existence of a surface barrier or exclusively caused by bulk pinning. The action of both the surface and the bulk barriers is evidenced. At 70 K, a very high critical current density of the surface currents is determined, which is higher than the critical current density of the bulk. The field and temperature dependence of the pinning behaviour reflects mainly bulk pinning in 2D. The measurements were repeated after 4 and 12 months to investigate the influence of aging. A destruction of the superconducting properties of the grain boundaries accompanied by a degradation of the surfaces of the grains with time is proved.     

AlGaN/GaN HEMT器件电流坍塌和膝点电压漂移机理的研究

考虑了势垒层、缓冲层体陷阱及表面电荷的浓度变化对电流坍塌和膝点电压的影响,发现表面电荷和势垒层体陷阱浓度的变化对沟道电子的浓度影响较小,表面电荷浓度变化下的膝点电压的偏移和坍塌强度的大小与势垒层势阱能量的变化有着主要的关系.缓冲层有着比势垒层更强的局域作用,势垒层和缓冲层的体陷阱浓度在一定范围变化时的膝点电压偏移主要是由沟道电子浓度的变化而引起的,但偏移量却比表面电荷浓度变化的情况下小很多.势阱能量的变化是造成膝点电压偏移的重要原因,坍塌强度主要取决于势阱能量和沟道的电子浓度. 关键词： AlGaN/GaN高电子迁移率晶体管 电流坍塌 膝点电压 陷阱俘获