MOS电容微分量的频率特性——确定Si/SiO_2界面态密度分布及俘获截面的一种新方法

本文用单一能级界面态模型和均匀连续分布界面态模型研究了MOS电容微分量((de)/dv)与频率ω的关系,得到了归一化的(1-e/c_i)~3d/dV(e/ci)-V及(1-e/c_i)~(-3)d/dV(e/c_i)-ω解析式;用非均匀分布模型研究了界面电荷随机涨落的影响,并且,数字计算了相应的曲线.(1-e/c_i)~(-3)d/dV(e/c_i)-ω曲线是具有峰值的谱线,其峰值、峰位分别与界面态密度及发射时间常数相关.此谱线的峰值、峰位与 MOS栅压的关系对应界面态密度及发射时间常数的能量分布.这种方法与电导技术类似,具有可以同时得到态密度及俘获截面数据的优点.实验结果与理论计算结果相符合.     

衬底参数及界面特性对硅异质结电池性能的影响

针对a-Si:H(n)/c-Si(p)双面异质结太阳电池结构,数值研究了不同p型单晶硅衬底厚度、氧缺陷密度、电阻率以及异质结界面缺陷态密度与电池转化效率之间的关系.结果表明:异质结界面缺陷态密度是影响电池性能的最主要因素,衬底前表面界面缺陷密度增大,主要降低开路电压和填充因子,衬底背表面界面缺陷态密度主要影响短路电流和填充因子.其次,p型硅衬底厚度减小和氧缺陷密度的增大,均导致短路电流密度下降,电池转化效率降低,特别是在界面缺陷态密度较低时,氧缺陷密度对电池性能影响较大;最后,在衬底前表面界面缺陷态密度为5×1010 cm-2,后表面界面缺陷态密度为5×1010 cm-2以及氧缺陷密度为109 cm-2时,衬底电阻率存在最优值1 Ω·cm.     

a-Si TFT亚阈特征参数与有源层的厚度效应

从异质界面处的有效界面态出发 ,研究了 a-Si Nx:H/a-Si:H异质结 a-Si:H TFT的亚阈特征参数的界面效应和有源层的厚度效应 ,发现 a-Si:H的特性不仅与材料、工艺有关 ,而且其几何结构参数对 a-Si:H TFT的特性也有明显的影响。实验结果表明 :亚阈特征参数主要由异质界面的有效界面态密度决定 ,当 NH3/Si H4 比增加时亚阈特征参数下降 ,增加 a-Si Nx 材料的淀积温度 ,可使亚阈特性得到明显的改善 ,a-Si:H有源层的厚度减小 ,抑制了亚阈参数的增加 ,阈值电压也减小并趋于稳定 ,且 TFT的 ION/IOF F随有源层厚度呈现近似抛物线状变化规律。文中从理论上分析了有源层厚度与 TFT特性的关系 ,计算的最佳有源层的厚度约为 2 0 0 nm,这与实验结果基本一致。     

Si/GaAs异质结界面态及其价带不连续性

本文报道用自洽EHT方法研究Si/GaAs异质结界面态分布和价带不连续性。用准共度晶格模型处理晶格失配问题,并对晶格常数作了修正。通过对Si/GaAs(111)、Si/GaAs(111)和Si/GaAs(110)异质结中Si应变和GaAs应变的情况,分别进行计算,得到界面态分布和价带不连续值等物理量,结果表明:它们不仅依赖于组成异质结的两种材料的体性质,而且还依赖于界面晶向和材料应变。文中给出了这些计算结果,并作了初步的讨论。     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用.     

用电导法测定Si-SiO_2低界面态密度和俘获截面

<正> 本文用国产仪器完成了电导法的测量装置,对氯化氢氧化的硅样品测量结果表明,能够可靠地获得界面态密度几乘 10~9cm~(-2)·eV~(-1)的测量数据和相应的俘获截面. 已知,N型衬底MOS电容中界面态的等效并联电导G_p为:     

基于c-Si(P)衬底的a-Si/c-Si异质结模拟研究

本文中研究了影响 a-Si/c-Si 异质结界面复合的主要因素： 表面固定电荷 ,缺陷态载流子俘获界面： ,以及界面缺陷态密度 。当缺陷能级 接近c-Si本征能级,且 满足时,缺陷态复合中心复合速度达到最大。AFORS-HET 软件模拟显示, a-Si/c-Si界面能带不连续显著影响电池Voc、界面缺陷态密度大于1*1010 cm-2.eV-1时,界面态密度的增加会严重降低电池Voc,但其对电池电流密度影响不大。对于c-Si (P)/a-Si (P ) 结构异质结,C-Si衬底的势垒 和a-Si材料内的势垒 对降低c-Si (P)/a-Si (P ) 结构的接触电阻和界面复合速度,表现各不相同。     

ZnO/p-Si异质结的I-V及C-V特性研究

通过磁控溅射Al掺杂的ZnO陶瓷靶,在p-Si片上沉积n型电导的ZnO薄膜而制备了ZnO/p-Si异质结,并通过测试其光照下的I-V、C-V特性对其光电特性以及载流子输运特性与导电机理进行了研究。研究表明ZnO/p-Si异质结存在良好的整流特性与光电响应,可以广泛应用在光电探测和太阳电池等领域。由于在ZnO/p-Si异质结界面处的导带补偿与价带补偿相差太大的缘故,在正向电压超过1V时,导电机理为空间电荷限制电流导电。同时,研究表明ZnO/p-Si异质结界面存在大量界面态,可以通过减小界面态进一步提高其光电特性。     

HEMT及其界面态效应的二维数值模拟

本文提出了一个调制掺杂异质结界面态模型,并首次将界面态效应引入到HEMT的二维数值模型中.本文用基于异质结漂移-扩散模型建立的 HEMT二维数值模型对常规结构的 AlGaAs/GaAs HEMT进行了模拟,讨论了 HEMT的内部工作机制,特别是异质结效应.本文着重模拟分析了HEMT中界面态对器件性能的影响。模拟结果表明界面态对HEMT的特性有显著的影响.     

A single-frequency approximation for interface-state density determination

Fast interface state densities in the SiSi₂ system can be determined by measurements of the MIS capacitor admittance. Traditional detailed analysis require elaborate frequency dependent techniques. The more commonly used approximation techniques are difficult to interpret for interface state densities less than 1 × 10¹¹ eV^?1 cm^?2. We present here a new single frequency technique as an approximation method which provides quantitative criteria on the quality of such interfaces. The data required are a single high frequency capacitance vs voltage measurement and a corresponding conductance vs voltage measurement. The validity of this technique is best demonstrated in a three-dimensional plot of conductance, frequency and voltage. This also gives added insight into the relationship between the temporal and thermodynamic properties of interface electronic states. Comparison of results using this approximation to more detailed treatments demonstrates the validity of this new method for low surface state density determination in a range from 7 × 10⁹ eV^?1 cm^?2 to 8 × 10¹¹ eV^?1 cm^?2.     

Characterization of a-Si:H and a-SiGe:H p-i-n and Schottkyjunctions by admittance circuit modeling

The midgap density of states (MGDOS) and junction properties of a-Si:H and a-SiGe:H alloys are investigated by admittance measurements on p-i-n solar cells. An expression for the capacitance is derived from the frequency, temperature, and bias dependence of the deep state response. The measured admittance is analyzed with an equivalent circuit model. The density of states g₀, attempt-to-escape frequency, and the Fermi energy are adjusted to fit the measured admittance. Close agreement is found with the measured capacitance and conductance over a wide range of temperature and frequency. The single junction model is shown to apply equally well to p-i-n and Schottky diodes, justifying the neglect of the n-i junction and thin doped layers in the p-i-n device analysis. Fitted values of g₀ are confirmed by values of g₀ obtained from the limiting capacitance at high temperature     

Characterization and modeling of IMPATT oscillators

A method has been found for large-signal characterization of IMPATT diodes. Waveguides of different heights are used so that the effect on efficiency of load impedance at a fixed oscillation frequency can be observed. Experimental large-signal admittance plane plots for two p-n diodes operating in Ku-band are presented. A nonlinear phenomenological model of an IMPATT oscillator is developed which correctly predicts the experimentally observed dependence of efficiency on load conductance and admittance plane characteristics. In addition to aiding the visualization of oscillator performance, analysis of this parallel circuit model shows that efficiency increases rapidly with small-signal negative conductance.     

Impact of weak Fermi-level pinning on the correct interpretation of III-V MOS C-V and G-V characteristics

The commonly encountered frequency dispersion and distorted behavior of GaAs and III-V MOS C-V and G-V is clarified by using MOS interface state theory. The relation of the C-V behavior with Fermi-level pinning of III-V MOS is explained. It is shown why it is difficult to quantify the interface state density using the conductance method for III-V MOS. A qualitative distinction of interface state behavior from common frequency dispersion due to series resistance is also put forward and guidelines are given to properly interpret III-V admittance data.     

非对称单脊波导孤立缝导纳

本文建立了非对称单脊波导孤立缝谐振电导值的数学模型,给出了实例的理论计算结果和实验结果,两者比较有很好的一致性。本文还进一步用实验的方法研究了非对称单脊波导孤立缝导纳特性,这些数据对非对称单脊波导裂缝天线的设计有着重要的意义。     

Large signal circuit characterization of solid-state microwave oscillator devices

A method of direct measurement of the admittance in X band seen by an encapsulated solid-state oscillator embedded in microwave hardware is described. It is applicable to many two-terminal devices in waveguide, coaxial line or microstrip circuit configurations. The criterion for oscillation in negative conductance oscillators is used in conjunction with these admittance measurements to determine the complete frequency-dependent 'device-plane' of Gunn and IMPATT devices in S4 (pill-prong) encapsulations, and the forms of negative conductance and susceptance variation with RF voltage amplitude and frequency have been extracted for each of these devices. It is found that for transferred-electron devices in particular, the frequency dependence of these parameters over X band is very marked. The use of the admittance measuring technique to characterize the microwave circuit is discussed with reference to the improvement of AM and FM noise by the controlled insertion of perturbations in the admittance locus, and an example is given of its use in fault-finding in a mechanically tunable waveguide oscillator.     

Frequency conversion in IMPATT diodes

A large-signal model of the Read-type IMPATT diode has been used to analyze the frequency-mixing properties of the oscillating diode. The self-oscillating, two-port frequency converter is described in terms of its short-circuit admittance parameters. It is shown that in the proper circuit, parametric frequency conversion may result in a negative conductance at the input and output ports of the converter. Therefore, high-gain frequency conversion and parametric amplification are possible. Under some conditions, spurious oscillations may occur due to this negative conductance. Experimental circuits have been built which demonstrate conversion gain and parametric amplification and confirm qualitatively the theoretical results. It is also shown experimentally that some of the sideband noise of the IMPATT oscillator is due to low-frequency noise which is up converted from the bias circuit. Some of this noise can be eliminated by proper circuit design.     

The admittance of the infinite cylindrical antenna immersed in a lossy, compressible plasma

Some numerical results obtained from an analysis of the admittance of an infinite cylindrical antenna excited at a circumferential gap of finite thickness and immersed in a lossy, compressible (warm) plasma are given. The linearized hydrodynamic equations are used for the electrons (ion motion is neglected). A free-space layer, or vacuum sheath, is used to approximate the ion sheath which forms about an object at floating potential in a nonzero temperature plasma. Values for the antenna admittance are obtained by a direct numerical integration of the Fourier integral for the current, and are presented as a function of frequency for plasma parameter values typical of theEregion of the ionosphere. The admittance exhibits a maximum below the plasma frequency unless the electron temperature and sheath thickness are both zero; however, above the plasma frequency, the sheath and electron temperature have relatively little effect on the antenna admittance. The nonzero plasma temperature considerably enhances the antenna conductance below the plasma frequency compared with the zero-temperature case while at the same time reducing the dependence of the conductance on the electron collision frequency. A susceptance zero the location of which is not sensitive to the vacuum sheath thickness occurs near the plasma frequency.