用深能级瞬态电容谱测定掺磷-Si:H的隙态密度

正 非晶硅的隙态密度在很大程度上决定了材料的电学和光学性质,因而对非晶硅隙态密度的研究具有重要的理论和实际意义。目前,对非晶硅隙态密度分布的认识,仍存在着争议。W.E.Spear.等人首先用场效应方法测定了非晶硅的隙态密度分布,并在相当一段时间为人们所接受。但由于场效应方法在实验数据处理上存在着很大误差。另外该方法的测量结果受界面态的影响很大。J.D.Cohen等人用深能级瞬态谱(DLTS)测     

空间电荷限制电流法对a—Si：H隙态密度的测量

本文介绍了用于测量ａ－Ｓｉ：Ｈ隙态密度的空间电荷限制电流（ＳＣＬＣ）法，并报道了采用此方法对ＰＥＣＶＤ方法制备的ａ—Ｓｉ：Ｈ材料隙态密度的测量结果。对ｎ＋ａ—Ｓｉ：Ｈ／ａ—Ｓｉ１Ｈ／ｎ＋ａ—Ｓｉ：Ｈ结构的样品，测量得到费米能级上０．１６ｅＶ间的欧态密度分布为１０１５～１０１８（ｃｍ－３ｅＶ－１）。     

非晶硅隙态密度的场效应测量分析方法

本文通过引入一个“电场函数”使非晶硅隙态密度的场效应测量的分析大大简化,并确立了从实验测得的电流-电压曲线极小值来确定电子电导与空穴电导的比值的方法,使对场效应测量结果的分析更加方便和可靠.还从Goodman等所采用的四条隙态密度分布曲线出发,计算出各有关参量,证明了不同态密度分布并不能与同一条电流-电压曲线拟合.这说明,如果采用合理的分析方法,是可以根据场效应测量结果来确定隙态密度分布的.     

掺过渡金属钴的非晶硅薄膜的ESR和光电特性的研究

本文对用电子束蒸发法制备的a-Si:Co薄膜的ESR和光学特性进行了研究.对样品的ESR信号、光学带隙和室温电导率随杂质浓度的变化关系进行了测量.结果表明,Co原子在a-Si:Co薄膜中形成受主中心,并伴随着对悬挂键的补偿;当杂质浓度小于3％时,光学带隙、自旋态密度和峰峰宽度基本不变,当杂质浓度大于3％时,随着Co含量的增加,光学带隙、自旋态密度减小,室温电导率和峰峰宽增大.本文对上述结果进行了分析和讨论.     

用光热偏转光谱技术测量a-Si:H/a-SiN_x:H多层膜的能隙态密度

用光热偏转光谱技术测量了不同a-Si:H层厚度的a-Si:H/a-SiN_x:H多层膜(超品格)材料的吸收光谱,求出多层膜材料的隙态密度及其随a-Si:H层厚度的变化,估算出界面态密度为～5×10~(11)cm~(-2)eV~(-1),最后估算了隙态密度的计算误差。     

太赫兹波在二维三角晶格光子晶体中的传播特性

用平面波展开法研究了太赫兹波在二维三角晶格光子晶体中的传播特性。数值计算了以硅为背景的空气圆柱构成的二维三角晶格光子晶体的能带结构和态密度,计算表明r=0.50a和r=0.46a时,E偏振和H偏振分别出现最大光子带隙,带隙宽度分别0.1097THz和0.1935THz,在r=0.48a出现最大完全光子带隙,带隙宽度为0.0759THz,光子晶体态密度的分布也表明了存在光子带隙的范围,研究结果为太赫兹器件的开发提供了理论依据。     

光电导归一化法测量-Si:H隙态密度

本文用光电导归一化法得出 -Si:H膜在低吸收区的光吸收系数谱;用电子从价带的指数尾态和导带边以下1.0 eV处,由悬挂键形成的局域态到导带扩展态的跃迁,解释了实验结果;并从而得出费米能级EF以下的隙态密度,通过对复合动力学的研究,还得到费米能级以上(EFn-EF)的局域态密度的平均值,从而得出费米能级以上部份的态密度。结果表明导带尾比价带尾窄。     

太赫兹波在二维光子晶体中的传播特性

为了得到太赫兹波在二维三角晶格光子晶体中的传播特性,利用平面波展开法数值模拟了三角晶格能带结构和态密度分布,得出E偏振当填充率f=0.9069和H偏振f=0.7346时出现最大光子带隙,在f=0.8358出现最大完全光子带隙.计算表明,增加介电常数的差值,太赫兹波在三角晶格光子晶体中传播的带隙增加了,光子晶体态密度的分布验证了存在光子带隙的范围.研究结果为太赫兹波器件的开发提供了理论依据.     

太赫兹波在光子晶体中的传输特性

为了研究太赫兹波在2维正方晶格光子晶体中的传播特性,利用平面波展开法数值模拟了光子晶体能带结构和态密度分布。计算表明,E偏振当填充率f=0.6362和H偏振当填充率f=0.7845时出现最大光子带隙,在f=0.7791出现最大完全光子带隙;增加介电常数的差值,也增加了太赫兹波在正方晶格光子晶体中传输的带隙;光子晶体态密度的分布验证了存在光子带隙的范围。研究结果为太赫兹波器件的开发提供了理论依据。     

太赫兹波段蜂巢晶格二维光子晶体传输特性的研究

运用平面波展开法优化了太赫兹波段蜂巢晶格二维光子晶体带隙结构,数值模拟得到了太赫兹波段蜂巢晶格光子晶体的最大TE模、TM模和完全带隙,通过光子晶体态密度分布进一步验证了所优化的带隙结构,并设计了对应带隙范围的太赫兹波器件。研究结果为太赫兹器件的开发提供了理论依据。     

氢化非晶硅薄膜晶体管的静态特性研究

发展了一种研究a－Si：HTFT静态特性的新方法。从a－Si材料的带隙态密度适配参数分布函数出发，采用Shockley－Read-Hall统计描述，发展了一种局域态电行密度统一模型，该模型同时考虑了带尾局域态和缺陷局域态的作用。提出并分析了沟道区有效温度参数的概念，在此基础上，推导出了a－Si：HTFT电流—电压特性的解析表达式。其理论值与实验值符合很好。并详细分析了a－Si材料参数对TFTN态特性的影响。     

Localized states near the band gap of GaAs caused by tetrahedral arsenic clusters

The method of 4×4×4 extended unit cells developed previously for calculating the electronic energy spectrum of gallium arsenide with defects is used to investigate the spectrum of gallium arsenide with simple arsenic clusters of tetrahedral symmetry containing 17 and 35 arsenic atoms. The waves functions and energies of localized states in the vicinity of the band gap are calculated, and electron density patterns are obtained. A comparative analysis is made of the energies and electron density of these states for various clusters. It is shown that localized states in the vicinity of the band gap can be interpreted as the result of splittings due to interactions of the host with the set of A ₁ levels generated in the band gap by noninteracting AsGa antisite defects that make up the cluster. The occupation of these states by electrons is discussed. Fiz. Tekh. Poluprovodn. 32, 1094–1099 (September 1998)     

Determination of interface-state density and mobility ratio in silicon surface inversion layers

A method has been proposed to deduce the energy distribution of interface states and the mobility ratio of carriers simultaneously from Hall effect measurements at two different temperatures. Using this method, the interface-state density Nssand the mobility ratiorof carriers were determined on both n-channel and p-channel silicon MOS transistors. The result indicates that Nssdetermined in this method is very small near the center of the energy gap and increases as the energy of the states approaches the band edges. The interface-state density inside the conduction and the valence band was found as high as 10¹³cm^-2eV^-1. The value of mobility ratio was found to depend both on temperature and surface-carrier density. Increase of mobility ratio with decreasing carrier density was observed in all samples, it is interpreted as due to diffuse scattering and to Coulomb scattering by localized interface charges.     

Sb掺杂SrTiO3电子结构的第一性原理计算

计算了Sb掺杂SrTi1-xSbxO3(x=0,0.125,0.25,0.33)体系电子结构,分析了掺杂对SrTiO3晶体的结构、能带、态密度、分波态密度的影响.所有计算都是基于密度泛函理论框架下的第一性原理平面波超软赝势方法.计算结果表明:体系的导电性与掺杂浓度有关,Sb掺杂在母体化合物SrTiO3中引入了大量的传导电子,费米能级进入导带.当Sb掺杂浓度x=0.125时,体系显示金属型导电性.同时,光学带隙展宽,且向低能方向漂移,可作为优良的透明导电薄膜材料.     

Sb掺杂SrTiO3电子结构的第一性原理计算

计算了Sb掺杂SrTi1-xSbxO3(x=0,0.125,0.25,0.33)体系电子结构,分析了掺杂对SrTiO3晶体的结构、能带、态密度、分波态密度的影响.所有计算都是基于密度泛函理论框架下的第一性原理平面波超软赝势方法.计算结果表明:体系的导电性与掺杂浓度有关,Sb掺杂在母体化合物SrTiO3中引入了大量的传导电子,费米能级进入导带.当Sb掺杂浓度x=0.125时,体系显示金属型导电性.同时,光学带隙展宽,且向低能方向漂移,可作为优良的透明导电薄膜材料.     

压力对NiO晶体结构及电子结构影响的理论研究

采用密度泛函理论的方法研究了不同压力条件下立方结构NiO氧化物的晶格结构、稳定性和电子结构。计算结果表明,NiO氧化物的晶格参数逐渐减小,键长变小,对称性保持不变;体系费米能先降低后增加;零压力下其存在着0.46eV的间接带隙,费米能级附近的状态密度较低,随着外压力的增加,带隙先减小再增大,费米能级附近的态密度先增大再减小。分析结果表明,随着外压力的增加,NiO氧化物价带顶附近的载流子有效质量先增大再减小;导带底的载流子有效质量均较小。外界加力还改变了NiO体系的电子分布情况。     

Energy gaps in the density of states of a graphene buffer layer on silicon carbide: Consideration for the irregularity of layer-substrate coupling

Green’s function and the density of states of epitaxial graphene formed on the surface of a semiconductor are derived in the diagonal approximation. A graphene buffer layer on silicon carbide is considered in detail. It is assumed that, in the buffer layer, there are two types of states, specifically, states weekly and strongly coupled with the substrate. It is shown that, if there is an energy gap in the density of states of the buffer layer, the existence of the gap and its width are defined by the states providing weak graphene-substrate coupling.     

Enhancement of refresh time in quasi-nonvolatile memory by the density of states engineering

The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive at-tention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However,the further exten-sion of the refresh time in quasi-nonvolatile memory is limited by the charge leakage through the p-n junction.Here,based on the density of states engineered van der Waals heterostructures,the leakage of electrons from the floating gate to the channel is greatly suppressed.As a result,the refresh time is effectively extended to more than 100 s,which is the longest among all pre-viously reported quasi-nonvolatile memories.This work provides a new idea to enhance the refresh time of quasi-nonvolatile memory by the density of states engineering and demonstrates great application potential for high-speed and low-power memory technology.     

氢化非晶硅带隙态密度光诱导变化的研究

报导了与Ｓｔａｅｂｌｅｒ－Ｗｒｏｎｓｋｉ效应相关的氢化非晶硅（α－Ｓｉ：Ｈ）带隙态密度的光诱导变化，结果表明光照将使α－Ｓｉ：Ｈ带隙上半部分态密度的分布发生变化，采用ＡＭ１太阳光谱＊光照两小时使得导带迁移率边以下０．７ｅＶ处的带隙态密度从４×１０１６ｃｍ－３ｅＶ－１，增大到１×１０１７ｃｍ－３ｅＶ－１。     

Majority carrier surface mobilities in thermally oxidized silicon

A method of evaluation of majority carrier field-effect mobilities in surface space charge regions is described. This method is also adapted for the determination of chargeable (fast) surface state distribution in the gap. Experimental results obtained with both p- and n-type thermally oxidized silicon samples are presented. In these samples, the surface state density was found to be less than 10¹⁰electronic states/cm²and thus were well suited for the evaluation of effective surface mobility by the dc field-effect measurements. The experimental mobilities are compared with those predicted by the theory of Greene et al. It was found that at flatband and at weak surface accumulation, measured values were lower than those theoretically predicted. For the case of strong surface accumulation, the opposite was true.