氢等离子体处理降低微晶硅薄膜的缺陷态密度

The effect of hydrogen plasma treatment(HPT) during the initial stage of microcrystalline silicon(μc-Si) growth on the defect density of μc-Si has been investigated. Lower absorption coefficient in the 0.8–1.0 eV indicated less defect density compared to its counterpart without HPT. The infrared spectroscopy of μc-Si with HPT shows an increase in 2040 cm-1, which reveals more Si–H in the amorphous/crystalline interfaces. We ascribe the decrease of defect density to hydrogen passivation of the dangling bonds. Improved performance of μc-Si solar cell with HPT is due to the reduced defect density.     

Reduced defect density in microcrystaUine silicon by hydrogen plasma treatment

Abstract： The effect of hydrogen plasma treatment （HPT） during the initial stage ofmicrocrystalline silicon （μc- Si） growth on the defect density of μc-Si has been investigated. Lower absorption coefficient in the 0.8-1.0 eV indicated less defect density compared to its counterpart without HPT. The infrared spectroscopy of μc-Si with HPT shows an increase in 2040 cm-1, which reveals more Si-H in the amorphous/crystalline interfaces. We ascribe the decrease of defect density to hydrogen passivation of the dangling bonds. Improved performance of μc-Si solar cell with HPT is due to the reduced defect density.     

Local density of states in photonic crystal cavity

Local radiative density of optical states (LDOS) offers a tool to control the radiative rate of spontaneous emission from molecules,atoms,and quantum dots,which is proportional to LDOS.This paper prese...     

提取悬挂的p型硅纳米梁的界面态密度和电阻率

The evaluation of the influence of the bending deformation of silicon nanobridges on their electrical properties is crucial for sensing and actuating applications.A combined theory/experimental approach for determining the resistivity and the density of interface states of the bending silicon nanobridges is presented.The suspended p-type silicon nanobridge test structures were fabricated from silicon-on-insulator wafers by using a standard CMOS lithography and anisotropic wet etching release process.After that,we measured the resistance of a set of silicon nanobridges versus their length and width under different bias voltages.In conjunction with a theoretical model,we have finally extracted both the interface state density of and resistivity suspended silicon nanobridges under different bending deformations,and found that the resistivity of silicon nanobridges without bending was 9.45 mΩ·cm and the corresponding interface charge density was around 1.7445×10¹³ cm^-2.The bending deformation due to the bias voltage slightly changed the resistivity of the silicon nanobridge,however, it significantly changed the distribution of interface state charges,which strongly depends on the intensity of the stress induced by bending deformation.     

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.     

Effects of tail states on the conduction mechanisms in silicon carbide thin films with high carbon content

Hydrogenated amorphous silicon carbide (a-SiC_x:H) films of different carbon content (x) were deposited by radio frequency plasma enhanced chemical vapor deposition (PECVD) system. Apart from the X-ray photoelectron spectroscopy (XPS) and UV-Visible transmission analyses, the resistivity measurements between 293 K and 450 K were emphasized to assess the eventual transport mechanisms. The film resistivities are unexpectedly found relatively low, especially for high carbon content. In the frame of exclusive band conduction, the apparent thermal activation energies, evaluated from Arrhenius type plot remain too low compared to half values of the optical gaps.Numerical analyses were undertaken by extending conduction from the band conduction about the mobility edge inside the band gap by including the nearest neighbor hopping (NNH) conduction across the localized tail states. By successfully fitting the formulated conductivity expression to the experimental results, parameters such as tail states distributions, true activation energies to the mobility edge have been retrieved.     

Influence of band gap of p-type hydrogenated nanocrystalline silicon layer on the short-circuit current density in thin-film silicon solar cells

The impact of the optical band gap (E_g) of a p-type hydrogenated nanocrystalline silicon layer on the short-circuit current density (J_sc) of a thin-film silicon solar cell is assessed. We have found that the J_sc reaches maximum when the E_g reaches optimum. The reason for the J_sc on E_g needs to be clarified. Our results exhibit that maximum J_sc is the balance between dark current and photocurrent. We show here that this dark current results from the density of defects in the p-layer and the barrier at the interface between p-and i-layers. An optimum cell can be designed by optimizing the p-layer via reducing the density of defects in the p-layer and the barrier at the p/i interface. Finally, a 6.6% increase in J_sc was obtained at optimum E_g for n-i-p solar cells.     

Role of barrier and buffer layer defect states in AlGaN/GaN HEMT structures

We have used low energy electron-excited nanoscale luminescence spectroscopy (LEEN) to detect the defects in each layer of AlGaN/GaN HEMT device structures to correlate their effect on two-dimensional electron gas (2DEG) confinement. Also, we have used Auger electron spectroscopy (AES) to detect the chemical composition as a function of lateral position on a growth wafer and to correlate chemical effects with electronic properties. We investigated several high-quality AlGaN/GaN heterostructures of varying electrical properties using incident electron beam energies of 0.5–15 keV to probe electronic state transitions within each of the heterostructure layers. The LEEN depth profiles reveal differences between sucessful and failed structures and highlight the importance of acceptor deep defect levels in the near 2DEG region. Variations in the GaN and AlGaN band edge emissions, as well as the yellow defect emission across an AlGaN/GaN heterostructure growth wafer have been observed. AES and LEEN spectroscopy of the growth wafer suggest that variation in the cation concentration may play a role in the mechanism responsible for the deep aceceptor level emission in the AlGaN barrier layer.     

Influence of the density of states on the open-circuit voltage in small-molecule solar cells

Open-circuit voltages are strongly dependent on the density-of-states in solar cells based on disordered semiconductors. In this work, organic solar cells based on tetraphenyldibenzoperiflanthene and fullerene C₇₀ with a bilayer structure were fabricated to investigate the variation in the density-of-states with the substrate temperature during deposition of the donor. The maximum open circuit voltage was reached at a substrate temperature of 60 °C. Organic thin-film transistors were also fabricated to study their electrical properties, such as the mobility and the density-of-states. Finally, an organic solar cell with p–i–n structure was fabricated at the optimized substrate temperature, and a power conversion efficiency of almost 4% was obtained.     

Effect of relative humidity and temperature on the stability of DNTT transistors: A density of states investigation

Exposure to moisture and elevated temperatures usually results in significant degradation of organic thin film transistor (OTFT) performance. Typical observations include reduced mobility, unstable threshold voltage and the appearance of hysteresis in electrical characteristics. In this contribution we investigate the effects of environmental conditions on OTFTs based on DNTT, a high-mobility, small-molecule, organic semiconductor, with polystyrene (PS) as the gate insulator. Device characteristics were measured after consecutive 30-min exposures to a relative humidity (RH) that was gradually increased from 20% to 80% with temperature fixed at 20 °C and for temperatures increasing from 20 °C to 90 °C with RH held at 10%. Despite significant negative shifts in turn-on and threshold voltages, only slight changes in the hole mobility were observed at the highest RH and temperature. The DNTT density of states (DoS) extracted from transfer characteristics in the linear regime using the Grünewald approach showed little change with environmental conditions. In all cases, the DoS decreased from ∼1 × 10²⁰ down to ∼1 × 10¹⁷ cm⁻³ eV⁻¹ in the 0.45 eV energy range above the hole mobility edge. Some evidence was obtained for a weak trap feature between ∼0.25 and 0.35 eV above the mobility edge. These results confirm the high stability of DNTT as a semiconducting material and that OTFT instability observed here is associated almost entirely with a flatband voltage shift caused by hole trapping in the polystyrene gate dielectric or at the polystyrene/DNTT interface.     

Assessing the width of Gaussian density of states in organic semiconductors

The Density of States (DOS) is an ingredient of critical importance for the accurate physical understanding of the optoelectronic properties of organic semiconductors. The disordered nature of this class of materials, though, renders the task of determining the DOS far from trivial. Its extraction from experimental measurements is often performed by driving the semiconductor out of thermal equilibrium and therefore requires making assumptions on the charge transport properties of the material under examination. This entanglement of DOS and charge transport models is unfavorable since transport mechanisms in organic semiconductors are themselves still subject of debate. To avoid this, we propose an alternative approach which is based on populating and probing the DOS by means of capacitive coupling in Metal Insulator Semiconductors (MIS) structures while keeping the semiconductor in thermal equilibrium. Assuming a Gaussian shape, we extract the DOS width by numerical fitting of experimental Capacitance–Voltage curves, exploiting the fact that the DOS width affects the spatial distribution of accumulated charge carriers which in turn concurs to define the MIS capacitance. The proposed approach is successfully tested on two benchmark semiconducting polymers, one of n-type and one of p-type and it is validated by verifying the robustness of the extraction procedure with respect to varying the insulator electrical permittivity. Finally, as an example of the usefulness and effectiveness of our approach, we study the static characteristics of thin film transistors based on the aforementioned polymers in the framework of the Extended Gaussian Disorder transport model. Thanks to the extracted DOS widths, the functional dependence of current on the gate voltage is nicely predicted and physical insight on transistor operation is achieved.     

The role of the density of interface states in interfacial energy level alignment of PTCDA

We introduce extensions to a recently developed numerical model to understand the origin of universal Fermi level pinning of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and its underlying mechanism. Our calculations are supported by ultraviolet and X-ray photoelectron spectroscopy to investigate the electronic structure of PTCDA on a wide range of substrates with different work functions and coupling interactions. For 20 nm thick layers of PTCDA, nearly unchanged hole injection barriers on all substrates are observed without any dependence on the type of substrate (unreactive, reactive or passivated metals and polymers). The simulation results demonstrate how the shape of the DOS near the interface has long-range influence on key parameters (e.g. the barrier to charge injection) of the entire organic film.     

Splitting and shift of hot magnetophonon resonance peaks in a two-dimensional electron gas

The splitting of the magnetophonon resonance peaks in a two-dimensional electron system is investigated as function of the electric field (or average electron velocity) for different values of the broadening of the Landau levels. We found that for small broadening the maxima in the magnetophonon oscillations are split into two peaks. A new physical interpretation is presented for this splitting which is based on the separate contributions of LO-phonon absorption and emission processes. A shift of the resonance maxima is found when the broadening of the Landau levels is large. A new explanation is given for the apparent temperature and electron density dependence of the optical phonon frequency in heterostructures as determined from magnetophonon resonance experiments. A mechanism is proposed which is able to produce the observed shift in the resonant position and which is consistent with an interaction with the optical phonon mode of the bulk material.     

Identification of the acceptor level V3+/2+ in GaAs and a new experimental observation of V2 in “low spin” ground state in GaAs

The results of optical absorption and deel level transient spectroscopy on various V-doped GaAs materials (n type Bridgman, n and p type liquid encapsulated Czochralski,n andp type liquid phase epitaxy) are reported. It is definitively shown that the single acceptor state of isolated vanadium is located atE _c -0.14 eV and that no mid gap-level related to isolated vanadium which could explain same reported semi-insulating properties of V-doped GaAs has been detected. From the analysis of the absolute photoionization cross section gs/sk _n ^o of the above level it is shown that V²⁺ is in a low spin state in accordance with recent theoretical predictions.     

激光远场激发表面波在开口缺陷处的散射回波

为了实现激光超声技术对表面缺陷的定量检测,采用有限方法模拟了激光激发的表面波与表面开口矩形缺陷作用的复杂过程,比较了近场和远场两种不同激发方式下相同接收点的位移信号,发现远场激发下各种模式转换波和反射表面波能充分分离,有利于分析表面波与缺陷作用的复杂过程。在远场激发方式下分别探讨了表面波与缺陷前沿和后沿的作用过程,提取缺陷产生的散射回波特征,并用惠更斯原理分析其产生原因。最后研究了缺陷深度和宽度变化对散射回波特征的影响。结果表明,散射回波特征点到达时间差与缺陷深度和宽度有线性关系。该研究为反问题估算缺陷尺寸提供了理论依据。     

激光诱导镍等离子体发射光谱Stark展宽和电子密度的空间分辨特性

在大气环境下利用脉冲Nd:YAG激光532nm输出烧蚀Ni靶,产生了激光等离子体。在350-600nm波长范围内测定了激光诱导等离子体中Ni原子的空间分辨发射光谱。得到了385.83nm发射光谱线的Stark展宽及其随径向的变化特性。由发射光谱线的强度和Stark展宽计算了等离子体电子密度,并讨论了激光等离子体的空间演化特性。结果表明,在沿激光束方向上,当距离靶表面0-2.5mm范围内变化时,谱线的Stark展宽、线移和电子密度都随距靶面距离的增大而先增大,在离靶面约1.25mm处时达到最大值,之后随距离的进一步增大而减小;电子密度在0.1-3.0 1016cm-3范围内变化。     

220kV变电站中刀闸接触缺陷对断路器保护的影响分析

220kV变电站作为我国电力系统中的核心枢纽,对电网的稳定、安全运行具有十分重要的意义.降低220kV变电站事故发生率,是整个电力系统稳定运行的基础和前提.本文对220kV变电站中刀闸接触缺陷对断路器保护的影响进行分析,并且对220kV变电站中刀闸接触缺陷处理方法进行探讨,旨在确保电力系统安全稳定运行.     

Origins of photoluminescence degradation in porous silicon under irradiation and the way of its elimination

Using of infrared (IR) and photoluminescence (PL) spectroscopy a comparative study of distinctions in composition and photoluminescence properties of porous silicon with different morphology was performed. Basing on the obtained experimental data and conventional theoretical models the main factors were found that have a negative effect on the intensity of PL in porous silicon and its degradation under the impact of directed irradiation in the visible range. With porous silicon as an example having the pores of 50–100 nm in size there was demonstrated a possibility for improving of these characteristics by its chemical treatment in polyacrylic acid.     

一维掺杂光子晶体的缺陷模和偏振特性研究

利用特征矩阵法研究了两种偏振光通过一维掺杂光子晶体的缺陷模特征和偏振特性,结果表明:S偏振光的缺陷模对应的入射角随着入射波长的增大而增大,而P偏振光的缺陷模对应的入射角却随着入射波长的增大而减小;P偏振光存在明显的"广义布儒斯特角"对应的允许带,其"广义布儒斯特角"随着入射波长的增大而减小,S偏振光不存在"广义布儒斯特角".