具有p波超流的一维非公度晶格中迁移率边研究

研究了具有p波超流的一维非公度晶格中迁移率边的性质. 发现适当的p波超流可以增加体系中的迁移率边的数目, 并且通过多分形分析确定了迁移率边所在的位置.     

Urbach tail and gap states in hydrogenated a-SiC and a-SiGe alloys

By combining photothermal deflection spectroscopy (PDS) and transmission measurements, the localized-state distribution inside the mobility gap has been optically investigated in amorphous silicon based alloys. For both silicon-carbon and silicon-germanium alloys, a rigid shift of the [seudo-gap is observed with increasing deviation from pure a-Si:H. The effect is accompanied by a significant broadening of the Urbach edge. We explain the latter in terms of potential fluctuations due to compositional disorder. For Ge-rich a-SiGe:H, the large density of defect states in the upper half of the gap makes this analysis less quantitative. In the carbon-based alloy, compositional disorder does not bring about additional defect related states throughout the range of compositions explored. This indicates that a-SiC:H, is a promising material for optoelectronic applications.     

Post-transit-time analysis of time-of-flight photocurrents

It is shown how the density of localized gap states in amorphous semiconductors can be deduced from time-of-flight photocurrents on the basis of the trap-limited band transport model, post-transit currents giving information on deep-state densities; and how strong deep-trapping of the photo-induced excess carriers invalidates the analysis. Results from a-Si:H, p-type a-Si:H, a-Si,S:H and a-Si,C:H samples are used to illustrate these points.     

Photo-induced electrical instability in hydrogenated amorphous silicon based thin-film transistors and the effect of its phase transition

We investigate the origin of photo-induced electrical instability in hydrogenated amorphous silicon based thin-film transistors (a-Si:H TFTs). Photo instability alone was accompanied by a positive shift in the threshold voltage (V_TH) caused by photo irradiation, and even larger positive or negative shift further exacerbated the instability caused by photo-induced electrical bias stress. Such phenomena can occur as a result of extended charge trapping and/or the creation of defect-states at the semiconductor/dielectric interface or in the gate dielectric. The mechanism for such is difficult to describe through chemical interactions of electron-donating and -withdrawing molecules that exhibit a shift in V_TH in only one direction. We also prove that a transition from an amorphous to a protocrystalline phase improves the photo-induced electrical stability. Such results originate from a reduction in the density of the localized states in protocrystalline-Si:H films relative to that of a-Si:H. We believe that this study provides significant information on the device physics of optoelectronics, which commonly exhibit photo-induced instability and charge transport, as a result of prolonged exposure to photo irradiation.     

Thermoelectric power,photo and dark conductivity of doped amorphous silicon

Summary Conductivity, photoconductivity and thermopower measurements have been made as functions of temperature on a series of p- and n-type a-Si: H films prepared by a reactive, evaporation method. The results have been fitted with a model including two conduction paths: in the high-temperature range through extended band states and in the low-temperature range as hopping in an impurity band, whose density of states increases with increasing dopant content. A shift of the Fermi level up to 0.4 eV towards the mobility edges for both types of dopants has been found. Moreover, phosphorus doping radiply increases the photoconductivity values by about two orders of magnitude, while boron incorporation causes considerable reduction. This work was supported in part by GNSM-CNR, MPI and CNR ?Progetto Finalizzato Energetica?.     

Subnanosecond transient photocurrents in a-Si:H: A probe of thermalization within shallow band-tail states

The measurement of transient photocurrents in amorphous semiconductors has been shown to be a powerful way of exploring the thermalization of excess carriers within the manifold of localized states adjacent to the band edges. The extent to which thermalization within the shallowest states can be resolved in controlled by the experimental observation time. Reported here are measurements of transient photocurrents, using high-speed stripline techniques, in glow-discharge a-Si:H carried out in the time regime (0.6 ? 100 nsec) and the temperature range 150 ? 320K. We find an effective electron drift mobility of <μ_D(t)> = 1–3 cm²/Vsec at t=0.6 nsec and T=300K and a time-dependent activation energy, _?(t), for the photocurrent magnitude. The initial photocurrent decay (t < 100 nsec) can be fit to a power-law, t^?n, and the temperature dependence of the dispersion parameter, α=1?n, is given by α=α₀+βT. In view of these results the nature of the band-tail near the conduction band edge is discussed.     

Gap states in hydrogenated amorphous silicon: A comparison of photoemission and photoconductivity results

We report photoemission results from which we directly determined the density of states g(E) in the gap of a-Si:H between the top of the valence band E_v and the Fermi level. At 0.4 eV above E_v, g(E) was found to be ≈1×10²⁰ cm^-3 eV^-1 in the undoped film; P-doping increased g(E) in this region whereas annealing reduced it. The photoconductivity-derived optical absorption spectrum matched the shape of the photoemission spectrum, and thus supports the explanation that the photoconductivity shoulder at photon energies in the region of 1.3 eV is due to transitions from localized states above the valence band to the conduction band.     

An Analysis of Infrared Stimulated Current in a-Si:H Based on a Model of Three-step Excitations

An analysia of the infrared stimulated current in a-Si:H is presented based on a model of three-step excited processes. Since the photon energy of the infrared (i.r.) stimulated beam is less than half of the band gap, generation of tho photon current under the infrared illumination is originated from the mechanism of a three-step excited process. To match with the experimental result, we find that the excitation rate b^′ from the lower localized atates to the higher localiied states In the band gap is much smaller than that from the valence band to localized states and from localixed atatee to the conduction band. The steady state value of the density of the free carriers only depends on b^′, average recombination time γ and density of localixed states g(E).     

a-Si:H结的横向光生伏特效应

本文通过理论分析研究了a-Si:H结中横向光生伏特效应的定态与瞬态特性。所得结果表明理论与实验非常符合。值得注意的是,按理论关系应用常规不掺杂a-Si:H特性值估算的两个重要参数(样品中的薄层电阻1/σ_s和传输时间T_m)均比由实验得出的值大得多。基于合理的分析。我们认为在a-Si:H层中平行于结输运的电子可能具有异乎寻常高的载流子迁移率。 关键词：     

Mobility edges and reentrant localization in one-dimensional dimerized non-Hermitian quasiperiodic lattice

The mobility edges and reentrant localization transitions are studied in one-dimensional dimerized lattice with nonHermitian either uniform or staggered quasiperiodic potentials.We find that the non-Hermitian uniform quasiperiodic disorder can induce an intermediate phase where the extended states coexist with the localized ones,which implies that the system has mobility edges.The localization transition is accompanied by the PT symmetry breaking transition.While if the non-Hermitian quasiperiodic disorder is staggered,we demonstrate the existence of multiple intermediate phases and multiple reentrant localization transitions based on the finite size scaling analysis.Interestingly,some already localized states will become extended states and can also be localized again for certain non-Hermitian parameters.The reentrant localization transitions are associated with the intermediate phases hosting mobility edges.Besides,we also find that the non-Hermiticity can break the reentrant localization transition where only one intermediate phase survives.More detailed information about the mobility edges and reentrant localization transitions are presented by analyzing the eigenenergy spectrum,inverse participation ratio,and normalized participation ratio.     

Equilibrium dangling bond densities and its related thin-film alloys

The equilibrium density of dangling bonds is calculated without resort to kinetic arguments. We find that this density depends on temperature and the position of the Fermi energy within the mobility gap. Comparing our results to experimental data on the defect density in doped and light-soaked a-Si : H and to data on related thin-film alloys we are able to distinguish equilibrium from non-equilibrium defect structures. Our considerations suggest that enhanced carrier densities not only drive the equilibrium towards higher defect densities but also enhance the speed of those kinetic processes that establish equilibrium on the microscopic scale.     

一类一维势场中电子态的研究

研究了在一维势场Ｖ_n＝λｃｏｓ（Ｑn＋ａｎ^ｖ）（０＜ｖ＜１）中运动的电子状态，计算了本征能量和本征态的局域化指数。对Ｑ＝２π／３，系统的能带由三个子能带构成。当λ小于２时，每个子带中有两个迁移率边界。研究了扩展态、局域态以及迁移率边界随参数λ，ν，α的变化。 关键词：     

a-Si:H/a-SiNx:H超晶格薄膜光致发光性质的研究

本文报道了a-Si:H/a-SiNx:H超晶格薄膜光致发光某些性质的研究。实验发现,这种超晶格薄膜光致发光的强度和峰值能量随交替层a-Si:H厚度,测量温度及光照时间等而变化。同时还发现,在阴、阳两极上,利用GD法沉积的样品,发光强度和峰值能量也有所不同。文中对这些实验结果作了初步解释。     

Design of multiple layered a-Si:H(F)/a-SiGex:H(F) films for enhancement in photoresponse in the near-infrared spectrum

Photo-electric properties of a-Si:H(F)/a-SiGe_x:H(F) multilayer films were investigated by measurements of optical absorption, and photoconductivity in both steady and transient modes with the repetition length and the difference in the optical gap between a-Si:H(F) and a-SiGe_x:H(F) as the variables. Measurements of primary photocurrent clarified that photosensitivity for the multilayer films extended to longer wavelengths of around 725 nm, while high resistivity was maintained despite of lowering the band gap.The drift mobility of electrons was measured by the time-of-flight technique, showing 10^–2-10^–3 cm²/Vs, while the drift mobility-lifetime products of electron was maintained to be 10^–7 cm²/V. On the other hand, the drift mobility of holes was 10^–3 cm²/Vs, which was the similar magnitude to that of a-Si:H(F).     

Broken symmetries in the reconstruction of ν=1 quantum Hall edges

Spin-polarized reconstruction of the ν=1 quantum Hall edge is accompanied by a spatial modulation of the charge density along the edge. We find that this is also the case for finite quantum Hall droplets: current spin density functional calculations show that the so-called Chamon–Wen edge forms a ring of apparently localized electrons around the maximum density droplet (MDD). The boundaries of these different phases qualitatively agree with recent experiments. For very soft confinement, Chern–Simons Ginzburg–Landau theory indicates formation of a non-translational invariant edge with vortices (holes) trapped in the edge region.     

Photoconductivity of amorphous semiconductors

An analysis of photoconductivity is presented for a material with a carrier mobility which decreases as a power law with time. We calculate the steady state and transient response, and show that the model applies to hydrogenated amorphous silicon and other amorphous semiconductors. In a-Si:H the effective mobility is obtained from 10^?6 to 1 sec. The recombination is of bimolecular type and the carrier density is almost independent of excitation intensity.     

Electrical properties and degradation behavior of hydrogenated amorphous Si alloys for solar cells

The electrical properties and the degradation behavior of hydrogenated amorphous silicon alloys (a-Si_1–x A _x : H, with A=C, Ge, B, P) in designs of pin, pip, nin, and MOS structures are investigated by measuring the dark and light I(V) characteristics and the spectral response as well as the space-charge-limited current (SCLC), the time of flight (TOF) of carriers and the field effect (FE). These investigations give an overview of our recent work combined with new results emphasizing the physics of the a-Si:H pin solar cells. We discuss the stabilizing influence on the degradation behavior achieved by profiling the i layers of the pin solar cells with P and B. Two kinds of pin solar cells, namely glass/SnO₂/p(C)in/metal and glass/metal/pin/ITO, are investigated and an explanation of their different spectral response behavior is given. SCLC measurements lead to the conclusion that trapping is also involved in the degradation mechanism, as is recombination. TOF experiments on a-Si_1–x Ge _x : H pin diodes indicate that the incorporation of Ge widens the tail-state distribution below the conduction band. FE measurements showed densities of gap states of about 5×l0¹⁶cm^–3eV^–1.     

Topologically protected edge gap solitons of interacting Bosons in one-dimensional superlattices

We comprehensively investigate the nontrivial states of an interacting Bose system in a cosine potential under the open boundary condition. Our results show that there exists a kind of stable localized state: edge gap solitons. We argue that the states originate from the eigenstates of independent edge parabolas. In particular, the edge gap solitons exhibit a nonzero topological-invariant behavior. The topological nature is due to the connection of the present model to the quantized adiabatic particle transport problem. In addition, the composition relations between the gap solitons and the extended states are also discussed.     

Trap statistics and the gap density of states in amorphous materials

We present a one-electron theory of non-equilibrium trap occupancy in amorphous materials, with simple results for electrons in states above the equilibrium Fermi level. The density of these states can then be obtained by analysis of transient photoconductivity. Specific values are given for a-Si: H samples for energies in the range 0.55–0.40 eV below the conduction band mobility edge. We conclude that the state density there can be low, as suggested by the results of deep level transient spectroscopy.