Strain-Gradient-Induced Modulation of Carrier Density and Mobility at the LaAlO3/SrTiO3 Heterointerface

A strain gradient induced by mechanical bending on a SrTiO₃ substrate is demonstrated, and has a pronounced influence on the carrier density and mobility of the interfacial 2D electron gas at the LaAlO₃/SrTiO₃ heterointerface. Tensile and compressive strain gradients represent two states of upward and downward bending. Under the tensile strain gradient, the carrier density decreases and the mobility has about 200% increase. Conversely, under the compressive strain gradient, the mobility decreases and the carrier density increases by up to 107%. These results demonstrate a range of opportunities to modulate the carrier density and mobility at oxide heterointerface and open up a promising way for further research on application of oxide devices.     

Determining the mobility of ions by transient current measurements at high voltages

We present polarization and transient current experiments that allow an independent determination of the charge carrier density and the mobility of ions in polymer electrolytes at low charge carrier density. The method relies on a complete depletion of ions in the bulk electrolyte achieved by applying high voltages. Based on a qualitative model for the charge dynamics in this nonlinear regime, the method is exemplarily applied to a system of polymethylmethacrylate doped with small amounts of a lithium salt. The independently obtained values for the ionic mobility, the charge carrier density, and the conductivity are consistent for all salt concentrations studied. Criteria for the applicability of the method are discussed.     

镧掺杂BaSnO3薄膜的电学和光学特性

利用射频磁控溅射法在(LaAlO₃)_0.3(SrAl_0.5Ta_0.5O₃)_0.7 (001)单晶基底上生长了镧掺杂BaSnO₃外延薄膜. 通过Hall效应和热电势测量证实了镧掺杂BaSnO₃薄膜具有n型简并半导体特征, 并且基于载流子浓度和Seebeck系数计算出电子的有效质量为0.31m₀ (m₀为自由电子质量). 镧掺杂BaSnO₃薄膜在可见波段具有良好的透明性(透过率大于73%). 基于介电模型对薄膜的透过率曲线进行拟合, 从拟合结果中不仅得到了薄膜的厚度为781.2 nm, 能带宽度为3.43 eV、 带尾宽度为0.27 eV和复光学介电常数随波长的变化规律, 而且也强力地支持了基于电学参数计算电子有效质量的正确性.     

Effects of edge chemistry doping on graphene nanoribbon mobility

Doping of semiconductor is necessary for various device applications. Exploiting chemistry at its reactive edges was shown to be an effective way to dope an atomically thin graphene nanoribbon (GNR) for realizing new devices in recent experiments. The carrier mobility limited by edge doping is studied as a function of the GNR width, doping density, and carrier density by using ab initio density functional and parameterized tight binding simulations combined with the non-equilibrium Green's function formalism for quantum transport. The results indicate that for GNRs wider than about 4 nm, the mobility scales approximately linearly with the GNR width, inversely proportional to the edge doping concentration and decreases for an increasing carrier density. For narrower GNRs, dependence of the mobility on the GNR width and carrier density can be qualitatively different.     

Non-Monotonic Evolution of Carrier Density and Mobility under Thermal Cycling Treatments in Dirac Semimetal Cd_3As_2 Microbelts

Tunable carrier density plays a key role in the investigation of novel transport properties in three-dimensional topological semimetals.We demonstrate that the carrier density,as well as the mobility,of Dirac semimetal Cd_3As_2 nanoplates can be effectively tuned via in situ thermal treatment at 350 K for one hour,resulting in non-monotonic evolution by virtue of the thermal cycling treatments.The upward shift of Fermi level relative to the Dirac nodes blurs the surface Fermi-arc states,accompanied by an anomalous phase shift in the oscillations of bulk states,due to a change in the topology of the electrons.Meanwhile,the oscillation peaks of bulk longitudinal magnetoresistivity shift at high fields,due to their coupling to the oscillations of the surface Fermi-arc states.Our work provides a thermal control mechanism for the manipulation of quantum states in Dirac semimetal Cd_3As_2 at high temperatures,via their carrier density.     

Optical study of the free-carrier response of LaTiO3/SrTiO3 superlattices

We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO_{3}/SrTiO_{3} superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface approximately 3x10;{14} cm;{-2}. This is probably due to the leakage of d electrons at interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We observed a carrier relaxation time approximately 35 fs and mobility approximately 35 cm;{2} V-1 s;{-1} at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO3.     

Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces

We report on a study of magnetotransport in LaAlO3 /SrTiO3 interfaces characterized by mobilities of the order of several thousands cm2/V s. We observe Shubnikov-de Haas oscillations whose period depends only on the perpendicular component of the magnetic field. This observation directly indicates the formation of a two-dimensional electron gas originating from quantum confinement at the interface. From the temperature dependence of the oscillation amplitude we extract an effective carrier mass m* ? 1.45 m(e). An electric field applied in the back-gate geometry increases the mobility, the carrier density, and the oscillation frequency.     

Effects of Low-Damage Plasma Treatment on the Channel 2DEG and Device Characteristics of AlGaN/GaN HEMTs

We investigate the effects of remote nitride-based plasma treatment on the channel carrier and device characteristics of AlGaN/GaN high electron mobility transistors(HEMTs).A 200 W NH₃/N₂ remote plasma causes little degeneration of carrier mobility and an increase in electron density due to surface alteration,which results in a decrease in sheet resistance and an increase in output current by 20-30%.Improved current slump,suppressed gate leakage current,and improved Schottk...     

低温生长砷化镓的超快光抽运-太赫兹探测光谱

本文采用光抽运-太赫兹探测技术系统研究了低温生长砷化镓(LT-GaAs)中光生载流子的超快动力学过程.光激发LT-GaAs薄层电导率峰值随抽运光强增加而增加,最后达到饱和,其饱和功率为54μJ/cm~2.当载流子浓度增大时,电子间的库仑相互作用将部分屏蔽缺陷对电子的俘获概率,从而导致LT-GaAs的快速载流子俘获时间随抽运光强增加而变长.光激发薄层电导率的色散关系可以用Cole-Cole Drude模型很好地拟合,结果表明LT-GaAs内部载流子的散射时间随抽运光强增加和延迟时间(产生光和抽运光)变长而增加,主要来源于电子-电子散射以及电子-杂质缺陷散射共同贡献,其中电子-杂质缺陷散射的强度与光激发薄层载流子浓度密切相关,并可由散射时间分布函数α来描述.通过对光激发载流子动力学、光激发薄层电导率以及迁移率变化的研究,我们提出适当增加缺陷浓度,可以进一步降低载流子迁移率和寿命,为研制和设计优良的THz发射器提供了实验依据.     

Characterization of the hole transport and electrical properties in poly(9,9-dioctylfluorene)

A systematic study of the hole transport and electrical properties in blue-emitting polymers as poly(9,9-dioctylfluorene) (PFO) has been performed. We show that the temperature dependent and thickness dependent current density versus voltage characteristics of PFO hole-only devices can be accurately described using our recently introduced improved mobility model based on both the Arrhenius temperature dependence and non-Arrhenius temperature dependence. Within the improved model, the mobility depends on three important physical quantities: temperature, carrier density, and electric field. For the polymer studied, we find the width of the density of states σ=0.115 eV and the lattice constant a=1.2 nm. Furthermore, we show that the boundary carrier density has an important effect on the current density versus voltage characteristics. Too large or too small values of the boundary carrier density lead to incorrect current density versus voltage characteristics. The numerically calculated carrier density is a decreasing function of distance from the interface. The numerically calculated electric field is an increasing function of distance. Both the maximum of carrier density and minimum of electric field appear near the interface.     

Half-metallicity induced by out-of-plane electric field on phosphorene nanoribbons

Exploring the half-metallic nanostructures with large band gap and high carrier mobility is a crucial solution for developing high-performance spintronic devices. The electric and magnetic properties of monolayer zigzag black-phosphorene nanoribbons (ZBPNRs) with various widths are analyzed by means of the first-principles calculations. Our results show that the magnetic ground state is dependent on the width of the nanoribbons. The ground state of narrow nanoribbons smaller than 8ZBPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. In addition, we also calculate the electronic band dispersion, density of states and charge density difference of 8ZBPNRs under the action of out-of-plane electric field. More interesting, the addition of out-of-plane field can modulate antiferromagnetic semiconductor to the half metal by splitting the antiferromagnetic degeneracy. Our results propose a new approach to realize half-metal in phosphorene, which overcomes the drawbacks of graphene/silicene with negligible band gap as well as the transitional metal sulfide (TMS) with low carrier mobility.     

Hall effect in granular materials

We show that in granular materials the Hall coefficient cannot, in general, be used to estimate directly the density of carriers, since it will depend on the ratio of the mobility within the grains to the conductivity mobility. The Hall voltage is predominantly determined within the individual grains, where the mobility may be quite large. On the other hand, the conductivity mobility may be considerably smaller due to a strong potential barrier between grains. The Hall coefficient depends on the ratio of these mobilities as well as on the carrier density.     

Transport properties of photo-excited carriers in slightly compensated Hg0.785Cd0.215Te

Photo-Hall measurements are presented for slightly compensated n-type Hg_0.785Cd_0.215Te at 4 K where the electron mobility is limited by charged scattering centers. Using a 10.6 μm laser as the optical source, we observe that the electron mobility passes through a maximum as a function of photo-excited carrier density. Mobility expressions based on the Kane-band model are modified to incorporate neutralization of charged scattering centers by photo-excited carriers. Calculated mobility values are found to be in satisfactory agreement with the data. The observed decrease in mobility for high carrier densities is attributed to electron-hole scattering. The mobility enhancement at lower carrier densities is explained in terms of neutralization of charged acceptors.     

Effects of contact resistance on the evaluation of charge carrier mobilities and transport parameters in amorphous zinc tin oxide thin-film transistors

Accurate determination of the charge transport characteristics of amorphous metal-oxide transistors requires the mitigation of the effects of contact resistance. The use of additional electrodes as voltage probes can overcome contact resistance-related limitations and yields accurate charge carrier mobility values, trap depths and temperature and carrier density dependencies of mobility as well as trap depths. We show that large differences in measured charge carrier mobility values are obtained when such contact resistances are not factored out. Upon exclusion of the contact resistance, the true temperature dependence of charge carrier mobility appears in the form of two clearly distinct mobility regimes. Analyzing these revealed mobility regions leads to a more accurate determination of the underlying transport physics, which shows that contact resistance-related artefacts yield incorrect trends of trap depth with gate voltage, potentially leading to a misconstruction of the charge transport picture. Furthermore, a comparison of low- and high-mobility samples indicates that the observed effects are more general.     

Parallel magnetic field induced giant magnetoresistance in low density quasi-two-dimensional layers

We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density quasi-two-dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the orbital motion arising from the finite layer thickness and the large Fermi wavelength of the quasi-two-dimensional system at low carrier densities.     

The effect of Te alloying on the electronic gap of a-Se

The effect on the electronic density of gap states in a-Se produced by the isoelectronic additive Te has been studied by a combination of drift mobility and xerographic measurements. Drift mobility experiments probe the shallow gap states which control photoinjected carrier transport. Addition of Te to Se in the nominal range 0–18 wt.% progressively decreases both electron and hole drift mobility while simultaneously increasing dispersion. The number and distribution of deep gap states which control injected carrier range have been determined in the same films from analysis of xerographic residual potentials. Taken together these measurements show that progressive addition of Te to a-Se increases the integrated number of deep traps and broadens the distribution of both deep and shallow transport interactive electronic gap states.     

TEA-CO2激光辐照HgCdTe图像传感器的实验研究

利用TEA-CO₂激光对碲铬汞(HgCdTe)图像传感器的干扰和损伤现象进行了实验研究,分析了干扰和损伤机理。探测器上激光能量密度小于255 mJ/cm2时,饱和像素仅出现在光斑区域,激光能量密度为425.8 mJ/cm2时,像素被损伤,观察到了弥散斑和暗环等现象。建立了探测器的激光辐照模型,计算了探测器的温升,讨论了温升与载流子浓度、迁移率的关系。分析认为,弥散斑的出现是探测器升温产生的热激发载流子浓度扩散所致,暗环的出现是迁移率与载流子浓度扩散共同作用的结果,像素的损伤则是因为温升导致汞的析出。     

单晶金刚石氢终端场效应晶体管特性

基于微波等离子体化学气相淀积生长的单晶金刚石制作了栅长为2μm的耗尽型氢终端金刚石场效应晶体管,并对器件特性进行了分析.器件的饱和漏电流在栅压为-6 V时达到了96 mA/mm,但是在-6 V时栅泄漏电流过大.在-3.5 V的安全工作栅压下,饱和漏电流达到了77 mA/mm.在器件的饱和区,宽5.9 V的栅电压范围内,跨导随着栅电压的增加而近线性增大到30 mS/mm.通过对器件导通电阻和电容-电压特性的分析,氢终端单晶金刚石的二维空穴气浓度达到了1.99×10~(13)cm~(-2),并且迁移率和载流子浓度均随着栅压向正偏方向的移动而逐渐增大.分析认为,沟道中高密度的载流子、大的栅电容以及迁移率的逐渐增加是引起跨导在很大的栅压范围内近线性增加的原因.