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本文分析了量子化极限情况下MOS反型层二维电子气(2DEG)定域态电子电导率的频率特性。主要内容:(1)用费密分布函数随频率变化导出了在2DEG两种主要导电过程的频率特性。即向迁移率边激发导电过程电导率σ_(ME)(ω)和可变程跳跃导电过程电导率σ_(VRH)(ω)。发现:σ_(ME)(ω)和σ_(VRH)(ω)是一个复数。(2)说明了σ_(ME)(ω)有较长时间常数τ_n,对应一个低频过程。σ_(VRH)(ω)有较短时间常数,对应一个高频过程。(3)理论与实验作了比较,拟合结果表明,在实验条件下,向迁移率边E_c激发时间常数τ_n3.6×10~(-6)。 相似文献
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以导电聚苯胺为空穴传输材料,制备了固态染料敏化太阳电池(DSC).利用强度调制光电流谱(IMPS)和强度调制光电压谱(IMVS)研究了TiO2多孔膜内的电子输运及复合过程.通过TiO2多孔膜内电子的平均传输时间(τd)和电子寿命(τn)及对IMPS实验数据的拟合,获得电子在TiO2膜内的有效扩散系数(Dn)和扩散长度(Ln).这些聚苯胺基电池中的τn值为相应的液体型电池的1/10倍左右,表明在该固体电池中存在严重的光生电子的复合过程,这很可能主要是与氧化态染料分子和导电电子间的复合有关.随着TiO2膜厚的增加,τn和τd均变小,但Dn和Ln随之增加,只有在合适的膜厚范围内才能获得较高的光伏性能.
关键词:
聚苯胺
染料敏化太阳电池
IMPS
IMVS 相似文献
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采用分子束外延技术对δ掺杂GaAs/AlxGa1-xAs二维电子气(2DEG)样品进行了生长. 在样品生长过程中, 分别改变掺杂浓度(Nd)、空间隔离层厚度(Wd) 和AlxGa1-xAs中Al组分(xAl)的大小, 并在双温(300 K, 78 K)条件下对生长的样品进行了霍尔测量; 结合测试结果, 分别对Nd, Wd及xAl与GaAs/AlxGa1-xAs 2DEG的载流子浓度和迁移率之间的关系规律进行了细致的分析讨论. 生长了包含有低密度InAs量子点层的δ掺杂GaAs/AlxGa1-xAs 2DEG 样品, 采用梯度生长法得到了不同密度的InAs量子点. 霍尔测量结果表明, 随着InAs量子点密度的增加, GaAs/AlxGa1-xAs 2DEG的迁移率大幅度减小, 实验中获得了密度最低为16×108/cm2的InAs量子点样品. 实验结果为内嵌InAs量子点的δ掺杂GaAs/AlxGa1-xAs 2DEG的研究和应用提供了依据和参考.
关键词:
二维电子气
InAs量子点
载流子浓度
迁移率 相似文献
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β-Ga2O3具有禁带宽度大、击穿电场强的优点,在射频及功率器件领域具有广阔的应用前景.β-Ga2O3(201)晶面和AlN(0002)晶面较小的晶格失配和较大的导带阶表明二者具有结合为异质结并形成二维电子气(twodimensional electron gas,2DEG)的理论基础,引起了众多研究者关注.本文利用AlN的表面态假设,通过求解薛定谔-泊松方程组计算了AlN/β-Ga2O3异质结导带形状和2DEG面密度,并将结果应用于玻尔兹曼输运理论,计算了离化杂质散射、界面粗糙散射、声学形变势散射、极性光学声子散射等主要散射机制限制的迁移率,评估了不同散射机制的相对重要性.结果表明,2DEG面密度随AlN厚度的增加而增加,当AlN厚度为6 nm,2DEG面密度可达1.0×1013 cm-2,室温迁移率为368.6 cm2/(V.s).在T<184 K的中低温区域,界面粗糙散射是限制2... 相似文献
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本文利用密度泛函理论结合非平衡格林函数的方法, 对 (GaAs)n(n=1-4)直线原子链与Au(100)-3×3两半无限电极耦合构成Au-(GaAs)n-Au纳米结点的电子输运性质进行了第一性原理计算. 在各结点拉伸过程中, 对其结构进行了优化, 得到各结点稳定平衡结构时Ga-As的平均键长分别为0.220, 0.224, 0.223, 0.223 nm, 平衡电导分别为2.328G0, 1.167G0, 0.639G0, 1.237G0; 通过对结点投影态密度的计算, 发现电子传输主要是通过Ga, As原子中px与py电子轨道相互作用形成的π键进行的. 在0-2 V的电压范围内, 对于(GaAs)n(n=1-3)的原子链的电流随电压增大而增大, I-V曲线呈线性关系, 表现出类似金属导电行为; 对于(GaAs)4原子链在0.6-0.7 V, 0.8-0.9 V的电压范围内却存在负微分电阻现象. 相似文献
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S. Fujita J.P. Riley C.C. Chen Ching-Lung Ko C.S. Raju T. Yamaguchi 《Journal of Physics and Chemistry of Solids》1973,34(12):2075-2089
The correlation function formula for the dynamic conductivity of a system of non-interacting electrons in the field of impurities is analyzed in terms of proper connected diagrams. By selecting those diagrams appropriate in the region of weak coupling and low impurity concentration, a set of coupled equations for the energy broadening γ (ω, ε, ns) and the energy shift Δ(ω, ε, ns) is derived, where both γ and Δ depend on the frequency ω of a probing field, the energy ε of the electron, and the concentration, ng, of impurities. With the assumption of a finite range potential, these equations are solved. It is found that γ (ω, ns) is smaller than that extrapolated value which the conventional expression γ0 for the low-concentration collision frequency would predict, in the entire region studied, that the difference γ0-γ becomes appreciable when the ratio of the average time between scatterings, τc, to the average duration of a scattering, τd, is 100 or less, that γ (ω, ns) decreases monotonically from its static value γ (0, ns), and becomes vanishingly small in the region ω≈1/τd, and that in the static limit (ω=0), γ=γ0[1?(2/π) (γ0τd)+…], that the energy shift Δ is positive, and increases from 0 and reach a peak of magnitude γ0 as ω is raised from 0. By using the γ and Δ obtained, the dynamic conductivity σ(ω, ns) for degenerated electrons is calculated. The deviation, σ-σ0, from the conventional expression σ0=(?i) (nee2/M) [ω-iΓ0]?1, (ne]=number density of electrons), for 0°K, is appreciable when the ratio τc/τd is 100 or less. The field-term correction, which arises from the modification of the scattering due to the probing field, is found to be negligible in the entire region studied. 相似文献
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Studies of dielectric relaxation and ac conductivity have been made on three samples of sodium tungsten phosphate glasses over a temperature range of 77–420 K. Complex relative permitivity data have been analyzed using dielectric modulus approach. Conductivity relaxation frequency increases with the increase of temperature. Activation energy for conductivity relaxation has also been evaluated. Measured ac conductivity (σm(ω)) has been found to be higher than σdc at low temperatures whereas at high temperature σm(ω) becomes equal to σdc at all frequencies. The ac conductivity obeys the relation σac(ω)=Aω S over a considerable range of low temperatures. Values of exponent S are nearly equal to unity at about 78 K and the values decrease non-linearly with the increase of temperature. Values of the number density of states at Fermi level (N(E F)) have been evaluated at 80 K assuming values of electron wave function decay constant α to be 0.5 (Å)?1. Values of N(E F) have the order 1020 which are well within the range suggested for localized states. Present values of N(E F) are smaller than those for tungsten phosphate glasses. 相似文献
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Electrical conductivity and dielectric measurements of ([C2H10N2]CdCl2(SCN)2)n were carried out from 200 Hz–5 MHz over a temperature range of 307–352 K. The frequency dependence of electrical data have been analyzed in two frameworks: the electrical modulus formalism with the Kohlrausch-Williams-Watts (KWW) stretched exponential function and the electrical conductivity by using the Jonscher’s power law σ′Tot(ω,T) = σDC(T) + A(T)ωs(T) in the frequency domain. The conduction mechanism is attributed to the nonoverlapping small polaron tunneling (NSPT) model. Furthermore, the dielectric data have also been analyzed in modulus and polarizability formalisms. The close values of activation energies obtained from the conductivity, the relaxation process, the electric modulus, and the complex polarizability data confirm that the transport is through ion-hopping mechanism. 相似文献
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The a.c. conductivity σ(ω) of ionic materials takes the form, σ(ω) = σ(0) + Aωn. The carrier hopping rate, ωp, is obtained from the new expression σ(0) = A ωpn and the carrier concentration is estimated from σ(0). The contribution of creation and migration terms to the activation energy for conduction may be determined from the thermal activation of σ(0) and ωp and the corresponding entropy terms quantified. Data have been analyzed for four widely different ionic materials: single crystal Na β-alumina, polycrystalline Li4SiO4, Ag7l4AsO4 glass and Ca(NO3)2/KNO3 glass and melt. For each, the carrier concentration and hopping rates have been obtained. 相似文献
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Frequency dependence of the real part of the conductivity σ1(ω) in the region of the transition from almost linear (s < 1) to quadratic (s ≈ 2) can indicate a change in the conduction mechanism (the transition from the variable-range to the fixed-range hopping with increasing frequency); in this case, the sharpness of the change in the slope of the frequency characteristic is related to the dependence of the preexponential factor of the resonance integral on the intercenter distance in the pair. The frequency dependence of the imaginary part of the conductivity σ2(ω) has no kink in the vicinity of the transition frequency ωcr, remaining almost linear. A large dielectric loss angle |cotγ| = |σ2|/σ1 can indicate that the imaginary part of the conductivity at ω < ωcr is defined by the larger zero-phonon contribution in σ2res the region of weak variation in the loss angle γ(ω), which significantly exceeds the relaxation contribution σ2res. 相似文献
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本文假设导致托卡马克反常电子输运的主要机制为由温度梯度所驱动的重整化电子磁漂移波。通过求解动力学过程自洽地导出了反常电子输运系数的定标律:D(T)=(c/ωpe)2{((ve/qR)2/2π+(vc/2)2)1/2-vc/2}。它在数值上与现有实验给出的AIcator定标律符合。在无碰撞(vc→0)情况下与Ohkawa定标津一致。同时分析了该定标律与Alcator定标律的偏离,并由此讨论了强磁场欧姆加热托卡马克达到热核点火的可能性。
关键词: 相似文献
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Low temperature a.c. conductivity of β-alumina is of the form σ(ω) = σ(ω) + Aωn. Both σ(0) and A are found to be thermally activated. Simple relationships, dependent on the value of n, are shown to exist between (i) the relative magnitudes of σ(0) and A and (ii) their respective activation energies. 相似文献
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