Electronic and interface state density distribution properties of Ag/p-Si Schottky diode

Electronic and interface state distribution properties of Ag/p-Si Schottky diode have been investigated. The diode indicates non-ideal current-voltage behavior with an ideality factor greater than unity. The capacitance-voltage (C-V) characteristic is linear in reverse bias indicating rectification behavior and charge density within depletion layer is uniform. From I-V and C-V characteristics, junction parameters such as diode ideality factor and barrier height were found as 1.66 and ?_B(I-V) = 0.84 eV (?_B(C-V) = 0.90 eV), respectively. The interface state density N_ss and relaxation time τ of the Schottky diode were determined by means of Schottky capacitance spectroscopy method. The results show the presence of thin interfacial layer between the metal and semiconductor.     

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I--V (current--voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.     

Hot carrier degradation and a new lifetime prediction model in ultra-deep sub-micron pMOSFET

The hot carrier effect (HCE) of an ultra-deep sub-micron p-channel metal-oxide semiconductor field-effect transistor (pMOSFET) is investigated in this paper. Experiments indicate that the generation of positively charged interface states is the predominant mechanism in the case of the ultra-deep sub-micron pMOSFET. The relation of the pMOSFET hot carrier degradation to stress time (t), channel width (W ), channel length (L), and stress voltage (Vd ) is then discussed. Based on the relation, a lifetime prediction model is proposed, which can predict the lifetime of the ultra-deep sub-micron pMOSFET accurately and reflect the influence of the factors on hot carrier degradation directly.     

Influence of optical interference and carrier lifetime on the short circuit current density of organic bulk heterojunction solar cells

Based on simple analytical equations, short circuit current density (J_SC) of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of J_SC; and obvious oscillatory behaviour of J_SC was observed as a function of thickness. At the same time, the influence of the carrier lifetime on J_SC also cannot be neglected. When the carrier lifetime is relatively short, J_SC only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and J_SC behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.     

AlGaN/GaN异质结载流子面密度测量的比较与分析

对MOCVD技术在蓝宝石衬底上生长的不同Al组分AlGaN/GaN异质结进行了范德堡法Hall测量和电容-电压(C-V)测量，发现Hall测量载流子面密度值大于C-V测量值，并且随着AlGaN层Al组分的增加，两种测量值都在增加，同时它们的差值也在增加.认为产生这一结果的原因有两方面.一方面，Ni/Au肖特基金属淀积在AlGaN/GaN异质结上，改变了AlGaN势垒层的表面状态，使得一部分二维电子气(2DEG)电子被抽取到空的施主表面态中，从而减小了AlGaN/GaN异质结界面势阱中的2DEG浓度.随着势垒层Al组分的增加，AlGaN层产生了更多的表面态，从而使得更多的电子被抽取到了空的表面态中.另一方面，由于C-V测量本身精确度受到串联电阻的影响，使得测量电容小于实际电容，从而低估了载流子浓度.     

Highly anisotropic and tunable charge carrier of monolayer phosphorus allotropes by bi-axial strain

The complex variation of electronic properties and carrier mobility of four typical allotropes of phosphorus are investigated using first-principles calculations of bi-axial strain. Our study shows that the electronic properties and carrier mobility of single-layer α-, β-, γ- and δ-P are sensitive to bi-axial strain, and that the carrier mobility can even be increased by several orders of magnitude under specific tensile or compressive strain. Moreover, the anisotropy of their mobility in the two-dimensional plane shows different changes according to the variation of the bi-axial strain. In particular, the electron mobility of α-P (γ-P) along the two main axis directions is reversed when the bi-axial strain increased by 5% (−4%). This transformation is mainly caused by changes in the effective mass anisotropy due to alterations in band dispersion under external strain, as illustrated by the distribution of effective mass anisotropy and the corresponding changes of electronic properties under strain.     

Numerical calculations of potential distribution in non-ideal quadrupole trap and simulations of anharmonic oscillations

A quadrupole ion trap consisting of electrode structures symmetric about z-axis is an important tool for conducting several precision experiments. In practice the field inside the trap does not remain purely quadrupolar, and can be calculated using numerical methods. We have used boundary element method to calculate the potential inside the truncated as well as symmetrically misaligned quadrupolar ion trap. The calculated potential values are fitted to multipole expansion and the weights of multipole moments have been evaluated by minimizing the least square deviation. The higher-order multipole contribution in the fabricated hyperbolic electrodes due to truncation and machining imperfections is discussed. Non-linear effects arising due to the superposition of octupole moment manifest as anharmonic oscillations of trapped ions in the non-ideal Paul trap. Theoretical simulations of non-linear effects have been carried out.      

The influence of interface states and bulk carrier lifetime on the minority carrier behavior in an illuminated metal/insulator/GaN structure

An influence of electronic states at an insulator/GaN interface on the behavior of excess holes in an ultraviolet-illuminated metal/ SiO₂/n-GaN structure has been studied by numerical simulations for weak (gate bias of −0.1 V ) and strong (−1 V ) depletion, in a wide range of excitation light intensities (from 10¹⁰ to 10²⁰ photons cm⁻² s⁻¹) and for various bulk carrier lifetimes (from 1 to 100 ns). It has been found that the interface states with densities of 10¹² eV ⁻¹ cm⁻² dramatically reduce the total (integrated in the whole GaN layer) density of photogenerated holes and thus degrade the sensitivity of the metal/insulator/GaN-based photodetector.     

Determination of trap depth and trap density in Se70Te30−xZnx thin films using thermally stimulated current measurements

In the present paper concentration of traps (N_t) and trap depth (E_t) have been calculated by thermally stimulated current (TSC) measurements in amorphous Se₇₀Te_30−xZn_x (x=2, 4) thin films. These measurements are carried out at three different heating rates. It is observed that the amount of thermally stimulated current gradually increases and the temperature (T_m), at which maxima in TSC occurs, shifts to higher temperatures with increasing heating rates (β) as expected. The trap depth is found to be quite different for x=2 and x=4. The concentration of traps also increases slightly at higher concentration of Zn.     

Enhanced dielectric properties and energy storage density of interface controlled ferroelectric BCZT-epoxy nanocomposites

Polymer nanocomposites with ferroelectric fillers are promising materials for modern power electronics that include energy storage devices. Ferroelectric filler, Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) nanopowder, was synthesized by sol-gel method. X-ray diffraction (XRD) studies confirmed the phase purity and the particle size distribution was determined by transmission electron microscopy (TEM). Extended aromatic ligand in the form of naphthyl phosphate (NPh) was chosen for surface passivation of BCZT nanoparticles. Surface functionalization was validated by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy using slurry technique. The dielectric constant of surface-passivated BCZT nanopowder was ~155, whereas pristine BCZT nanopowder dielectric constant could not be assessed due to high innate surface conductivity. Furthermore, BCZT–epoxy nanocomposite films were prepared and analyzed by differential scanning calorimetry (DSC), dielectric spectroscopy, dielectric breakdown strength (DBS), and scanning electron microscopy (SEM). Owning to stronger polymer–particle interface, dielectric measurements of 5 vol.% NPh surface functionalized BCZT–epoxy nanocomposites indicated improved DBS and glass transition temperature (T_g), reduced dielectric loss, and enhanced energy storage density compared to untreated BCZT–epoxy composites and pure epoxy. The energy storage density of 30 vol.% NPh surface functionalized BCZT–epoxy nanocomposite of 20 μm film thickness was almost three times that of pure epoxy polymer of identical film thickness.     

晶硅太阳电池中Fe-B对与少子寿命、陷阱浓度及内量子效率的相关性

以太阳电池级直拉单晶硅片为材料,利用瞬态微波反射光电导衰减仪研究了硅片分别经过单、双面扩散后Fe-B对与少子寿命τ、陷阱浓度及制备成电池的内量子效率（IQE）的相关性.对于单面扩散后的样品,Fe-B对浓度分布在较大程度上决定了少子寿命分布;对于双面扩散后的样品,Fe-B对浓度显著降低（在135×10¹¹ cm^-3左右）,已不及其他杂质和缺陷对少子寿命的影响.结合瞬态微波衰减信号和陷阱模型,对单、双面吸杂前后硅片的陷阱浓度进行数值计算,发现经过扩散 关键词： 少子寿命 陷阱浓度 内量子效率 Fe-B对     

线性低密度聚乙烯中空间电荷陷阱的能量分布与空间分布的关系

使用激光感应压力波法和热刺激放电技术,系统地研究了直流高压作用下线性低密度聚乙烯(LLDPE)半导性电极试样中空间电荷的形成和演变及电荷陷阱分布和退极化过程.在直流高压作用下试样中空间电荷的分布明显地表现为两电极同极性电荷快速对称注入的特征,半导性电极与LLDPE的界面近乎呈现欧姆接触特征.LLDPE中的电荷陷阱分布表现出体内为浅陷阱、表层为深陷阱的特征.半导性电极与LLDPE薄片间的压合条件或电极材料对LLDPE表层的掺杂显著地影响表层陷阱的能量分布,导致表层中较深陷阱的深度和密度减小、较浅陷阱的密度增大.在整个短路退极化过程中,试样中正、负电荷的中心分别向距它们较近的电极迁移,而在开路退极后期则表现为与短路时不同的行为、被表层深陷阱再俘获的电荷脱阱后向背电极迁移. 关键词： 线性低密度聚乙烯 空间电荷 陷阱分布 热刺激放电     

First principles study on the charge density and the bulk modulus of the transition metals and their carbides and nitrides

A first principles study of the electronic properties and bulk modulus （B0） of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.     

Study on current density distribution of electron beam spots by wave optics theory

The image theory of wave electron optics is used to study the current density distribution of electron beam spots for high-resolution electron optical systems. Using the wave aberration concept and paraxial expansion of charge density, the space charge effect is taken into consideration by modification of paraxial rays and spherical aberration coefficient of the lens. The point spreading function is obtained by Fourier-Bessel transform of the optical transfer function considering the space charge and partial coherence of the electron source.     

Carrier density distribution in silicon nanowires investigated by scanning thermal microscopy and Kelvin probe force microscopy

The use of scanning thermal microscopy (SThM) and Kelvin probe force microscopy (KPFM) to investigate silicon nanowires (SiNWs) is presented. SThM allows imaging of temperature distribution at the nanoscale, while KPFM images the potential distribution with AFM-related ultra-high spatial resolution. Both techniques are therefore suitable for imaging the resistance distribution. We show results of experimental examination of dual channel n-type SiNWs with channel width of 100 nm, while the channel was open and current was flowing through the SiNW. To investigate the carrier distribution in the SiNWs we performed SThM and KPFM scans. The SThM results showed non-symmetrical temperature distribution along the SiNWs with temperature maximum shifted towards the contact of higher potential. These results corresponded to those expressed by the distribution of potential gradient along the SiNWs, obtained using the KPFM method. Consequently, non-uniform distribution of resistance was shown, being a result of non-uniform carrier density distribution in the structure and showing the pinch-off effect. Last but not least, the results were also compared with results of finite-element method modeling.     

聚光器聚焦光斑能流密度分布的测量与分析

采用基于CCD相机和朗伯靶的间接测量方法,对旋转抛物面聚光器焦平面和多个离焦面的能流密度分布进行了测量。研究了系统的标定方法,并对每个面内的光斑特性进行分析。结果表明：通过对各个接收面光斑特性的比较,可以判断聚光器真实焦点的位置;随着接收面离焦量的增大,光斑直径变大,能流密度峰值减小,形状越来越不规则。这项研究为聚光系统的热利用和接收器的设计提供了依据。     

Electrical and optical characterization of SiOxNy and SiO2 dielectric layers and rear surface passivation by using SiO2/SiOxNy stack layers with screen printed local Al-BSF for c-Si solar cells

In c-Si solar cells, surface recombination velocity increases as the wafer thickness decreases due to an increase in surface to volume ratio. For high efficiency, in addition to low surface recombination velocity at the rear side, a high internal reflection from the rear surface is also required. The SiO_xN_y film with low absorbance can act as rear surface reflector. In this study, industrially feasible SiO₂/SiO_xN_y stack for rear surface passivation and screen printed local aluminium back surface field were used in the cell structure. A 3 nm thick oxide layer has resulted in low fixed oxide charge density of 1.58 × 10¹¹ cm⁻² without parasitic shunting. The oxide layer capped with SiO_xN_y layer led to surface recombination velocity of 155 cm/s after firing. Using single layer (SiO₂) rear passivation, an efficiency of 18.13% has been obtained with V_oc of 625 mV, J_sc of 36.4 mA/cm² and fill factor of 78.7%. By using double layer (SiO₂/SiO_xN_y stack) passivation at the rear side, an efficiency of 18.59% has been achieved with V_oc of 632 mV, J_sc of 37.6 mA/cm², and fill factor of 78.3%. An improved cell performance was obtained with SiO₂/SiO_xN_y rear stack passivation and local BSF.     

On the comparative assessment of ratcheting-induced dislocation density in 42CrMo4 steel by X-ray diffraction profile analysis and hardness measurement

The phenomenon of ratcheting occurs under the influence of non-zero mean stress during cyclic loading; it singificantly reduces the low cycle fatigue life of engineering structures. The present investigation deals with a detailed comparison on the estimation of dislocation densities in the 42CrMo4 steel induced by ratcheting using two different methods, i.e. X-ray diffraction (XRD) profile analysis and hardness. The dislocation densities in the ratcheted specimens were assessed using XRD profile analysis following the modified Williamson–Hall method as well as hardness measurements following the modified Nix and Gao model. The results showed that dislocation density increased in the ratcheted specimens as compared to the unratcheted ones and increase in accumulation of ratcheting strain was correlated with the increase in dislocation densities in the ratcheted specimens. It was established that both hardness and X-ray diffraction profile analysis methods can very effectively be used to assess the dislocation densities in the ratcheted specimens.     

Comparison study of the charge density distribution induced by heavy ions and pulsed lasers in silicon

Heavy ions and pulsed lasers are important means to simulate the ionization damage effects on semiconductor materials. The analytic solution of high-energy heavy ion energy loss in silicon has been obtained using the Bethe-Bloch formula and the Kobetich-Katz theory, and some ionization damage parameters of Fe ions in silicon, such as the track structure and ionized charge density distribution, have been calculated and analyzed according to the theoretical calculation results. Using the Gaussian function and Beer's law, the parameters of the track structure and charge density distribution induced by a pulsed laser in silicon have also been calculated and compared with those of Fe ions in silicon, which provides a theoretical basis for ionization damage effect modeling.     

Comparison study of the charge density distribution induced by heavy ions and pulsed lasers in silicon

Heavy ions and pulsed lasers are important means to simulate the ionization damage effects on semiconductor materials. The analytic solution of high-energy heavy ion energy loss in silicon has been obtained using the Bethe-Bloch formula and the Kobetich-Katz theory, and some ionization damage parameters of Fe ions in silicon, such as the track structure and ionized charge density distribution, have been calculated and analyzed according to the theoretical calculation results. Using the Gaussian function and Beer＇s law, the parameters of the track structure and charge density distribution induced by a pulsed laser in silicon have also been calculated and compared with those of Fe ions in silicon, which provides a theoretical basis for ionization damage effect modeling.