Influence of temperature on strain-induced polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors

Electron mobility scattering mechanism in AlN/GaN heterostuctures is investigated by temperature-dependent Hall measurement, and it is found that longitudinal optical phonon scattering dominates electron mobility near room temperature while the interface roughness scattering becomes the dominant carrier scattering mechanism at low temperatures(～100 K).Based on measured current–voltage characteristics of prepared rectangular AlN/GaN heterostructure field-effect transistor under different temperatures, the temperature-dependent variation of electron mobility under different gate biases is investigated. The polarization Coulomb field(PCF) scattering is found to become an important carrier scattering mechanism after device processing under different temperatures. Moreover, it is found that the PCF scattering is not generated from the thermal stresses, but from the piezoelectric contribution induced by the electrical field in the thin AlN barrier layer. This is attributed to the large lattice mismatch between the extreme thinner AlN barrier layer and GaN, giving rise to a stronger converse piezoelectric effect.     

Influence of temperature on strain-induced polarization Coulomb field scattering in AIN/GaN heterostructure field-effect transistors

Electron mobility scattering mechanism in AlN/GaN heterostuctures is investigated by temperature-dependent Hall measurement, and it is found that longitudinal optical phonon scattering dominates electron mobility near room temperature while the interface roughness scattering becomes the dominant carrier scattering mechanism at low temperatures （~ 100 K）. Based on measured current-voltage characteristics of prepared rectangular AlN/GaN heterostructure field-effect transistor under different temperatures, the temperature-dependent variation of electron mobility under different gate biases is inves- tigated. The polarization Coulomb field （PCF） scattering is found to become an important carrier scattering mechanism after device processing under different temperatures. Moreover, it is found that the PCF scattering is not generated from the thermal stresses, but from the piezoelectric contribution induced by the electrical field in the thin A1N barrier layer. This is attributed to the large lattice mismatch between the extreme thinner AlN barrier layer and GaN, giving rise to a stronger converse piezoelectric effect.     

Effect of interface-roughness scattering on mobility degradation in SiGe p-MOSFETs with a high-k dielectric/SiO2 gate stack＊

A physical model for mobility degradation by interface-roughness scattering and Coulomb scattering is proposed for SiGe p-MOSFET with a high-k dielectric/SiO2 gate stack. Impacts of the two kinds of scatterings on mobility degradation are investigated. Effects of interlayer （SiO2） thickness and permittivities of the high-k dielectric and interlayer on carrier mobility are also discussed. It is shown that a smooth interface between high-k dielectric and interlayer, as well as moderate permittivities of high-k dielectrics, is highly desired to improve carriers mobility while keeping alow equivalent oxide thickness. Simulated results agree reasonably with experimental data.     

Deformation-induced dissolution of the intermetallics Ni3Ti and Ni3Al in austenitic steels at cryogenic temperatures

An anomalous deformation-induced dissolution of the intermetallics Ni₃Al and Ni₃Ti in the matrix of austenitic Fe–Ni–Al(Ti) alloys has been revealed in experiment at cryogenic temperatures (down to 77 K) under rolling and high pressure torsion. The observed phenomenon is explained as the result of migration of deformation-stipulated interstitial atoms from a particle into the matrix in the stress field of moving dislocations. With increasing the temperature of deformation, the dissolution is replaced by the deformation-induced precipitation of the intermetallics, which is accelerated due to a sufficient amount of point defects in the matrix, gained as well in the course of deformation at lower temperatures.     

Behavior at small distances and low temperatures of the ion-ion distribution function of the two-dimensional Coulomb gas

We compute upper and lower bounds for the canonical ion-ion distribution functiong ₁₁ ^(N) (r) of the two-dimensional Coulomb gas for smallr and 1<<2, where is the plasma parameter. Both bounds are proportional tor ^2-/(-1), which proves thatg ₁₁ ^(N) (r) behaves asr ^2-, as conjectured by Hansen and Viot. We conjecture that, in the thermodynamic limit,g ₁₁(r) ~ 2(-1)^-1(r/a)^2-, wherea=(n)^–1/2 is the mean interionic distance. We also compute the canonical one-body distribution function with one pair (+,–) in a disk, for anyr and any.     

Hole mobility and remote scattering in strained InGaSb quantum well MOSFET channels with Al2O3 oxide

Hall mobility and major scattering mechanisms in surface and buried MBE grown strained InGaSb quantum well (QW) MOSFET channels with in‐situ grown Al₂O₃ gate oxide are analyzed as a function of sheet hole density, top‐barrier thickness and temperature. Mobility dependence on Al_0.8Ga_0.2Sb top‐barrier thickness shows that the relative contribution of interface‐related scattering is as low as ～30% in the surface QW channel. An InAs top capping layer reduces the interface scattering even further; the sample with 3 nm total top‐barrier thickness demonstrates mobility of 980 cm²/Vs giving sheet resistance of 4.3 kΩ/sq, very close to the minimum QW resistance in the bulk. The mobility–temperature dependences indicate that the interface‐related scattering is dominated by remote Coulomb scattering at hole densities <1 × 10¹² cm^–2. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Local field correction effect on inelastic Coulomb scattering lifetime of two-dimensional quasiparticles at low temperatures

We have investigated the effect of local field correction on the inelastic Coulomb scattering lifetime of high mobility quasiparticles in a quantum layer at low temperatures. By replacing temperature-dependent dynamic dielectric function for the zero-temperature one in calculations, we have considered our improved zero-temperature STLS local field correction for low temperatures in lifetime calculations and compared the results with those obtained from the RPA and Hubbard approximation. It has been found that the quasiparticle lifetime decreases by including the STLS local field factor in all temperatures, energies and layer thicknesses.     

Direct measurements of electron thermalization in Coulomb blockade nanothermometers at millikelvin temperatures

We investigate electron thermalization of tunnel junction arrays installed in a powerful dilution refrigerator whose mixing chamber can produce lattice temperatures down to 3 mK. The on-chip Coulomb blockade thermometers (CBT) against other thermometers at the mixing chamber provide direct information on the thermal equilibrium between the electronic system and the refrigerator. We can detect and discriminate between the heat load delivered through the wiring and that produced by the bias current of the CBT-measurement. The basic heat leak limits the minimum of the electronic temperature to slightly below 20 mK.     

Angular and temperature‐related specific features of averaging of hole effective masses in p‐Ge at low temperatures

Microwave magnetoresistance of lightly doped (nondegenerate) p‐Ge has been studied by the electron spin resonance method, which can record the derivative of the microwave absorption with respect to the magnetic field. The change in the absorption is proportional to that in the conductivity of the semiconductor in the magnetic field (magnetoresistance). It was found that the averaging time of the light and heavy holes effective masses depends on temperature and on the magnetic field direction in a sample. An analysis of the derivative made it possible to determine regions of the fastest effective mass averaging.     

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18Al0.82N/AIN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.     

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In_(0.18) Al_(0.82) N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional(quasi-2D) model, the current–voltage(I–V) characteristics of In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors(HFETs) with different gate lengths are simulated based on the measured capacitance–voltage(C–V) characteristics and I–V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas(2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V·s for the prepared In0.18Al0.82N/AlN/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain–source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density,the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.     

Coulomb and nuclear interactions in the dynamics of weakly-bound neutron-halo breakup on heavy target

Within our aim to clarify some aspects of the breakup dynamics of loosely-bound neutron-halo projectiles on a heavy target,we apply the continuum discretized coupled-channel formalism to investigate the beryllium¹¹Be breakup on a lead²⁰⁸Pb target atE_lab=140 MeV incident energy.By evidencing that the continuum–continuum couplings are much stronger in the nuclear breakup than in the Coulomb breakup,we conclude that the strength of these couplings in the total breakup is dominated by the nuclear contribution,with the diagonal monopole nuclear potential in the projectile–target center-of-mass having negligible effect on the total and nuclear breakup cross-sections.For this kind of reaction,we show that the condition for the total breakup to approach its dominant component in the absorption region is strongly dependent on the continuum–continuum couplings and the diagonal monopole nuclear potential.     

埋氧层注氮工艺对部分耗尽SOI nMOSFET特性的影响

研究了埋氧层中注氮后对制作出的部分耗尽SOInMOSFET的特性产生的影响.实验发现，与不注氮的SIMOX基片相比，由注氮SIMON基片制作的nMOSFET的电子迁移率降低了.且由最低注入剂量的SIMON基片制作的器件具有最低的迁移率.随注入剂量的增加，迁移率略有上升，并趋于饱和.分析认为，电子迁移率的降低是由于Si/SiO2界面的不平整造成的.实验还发现，随氮注入剂量的提高，nMOSFET的阈值电压往负向漂移.但是，对应最低注入剂量的器件阈值电压却大于用SIMOX基片制作出的器件.固定氧化物正电荷及界面陷阱密度的大小和分布的变化可能是导致阈值电压变化的主要因素.另外发现，用注氮基片制作出的部分耗尽SOInMOSFET的kink效应明显弱于用不注氮的SIMOX基片制作的器件. 关键词： SOI nMOSFET 氮注入 电子迁移率 阈值电压     

Coulomb drag in the quantum Hall state: Role of disorder

We consider Coulomb drag between two layers of two-dimensional electron gases subject to a strong magnetic field, with the Landau level filling factor in each layer being . We find to be very large, as compared to the zero magnetic field case. We attribute this enhancement to the slow decay of density fluctuations in a strong magnetic field. For a clean system, the linear -dependence of the longitudinal conductivity, characteristic of the state, leads a unique temperature dependence – . Within a semiclassical approximation, disorder leads to a decrease of the transresistivity as compared to the clean case, and a temperature dependence of at low temperatures.     

Role of an additive in retarding coal oxidation at moderate temperatures

The impact of an additive on coal oxidation process is studied from the mechanistic perspective, aiming at development of a guideline in search of effective inhibitors for controlling the coal self-heating phenomena. The salt Na₃PO₄ was chosen as an additive. Behaviors of samples with/without the additive were examined at temperatures up to 400 °C both in oxidative and inert atmosphere using a TGA instrument, and the compounds on coal surface during oxidation and pyrolysis were monitored by FT-IR technique. The TGA data show that the impact of the additive on coal oxidation process can be directly evaluated using a parameter defined as the percentage of mass increase at ∼265 °C, and the addition of Na₃PO₄ slows down the rates of oxygen uptake and decomposition reactions. FT-IR results also indicate that the additive suppresses both the coal oxidation and pyrolysis processes essentially by accelerating the formation of saturated ether linkages. Further analysis suggests that Na₃PO₄ plays a role in modifying the routes for decomposition of hydroxyl, and subsequently improving the coal thermal stability.     

变温条件下受激布里渊散射增益系数的实验测量

从理论及实验上分析了介质温度对受激布里渊散射(stimulated Brillouin scattering, SBS)阈值及增益系数的影响.在理论分析的基础上, 提出了一种通过测量SBS阈值来决定介质SBS增益系数的新方法. 实验及测量结果表明, SBS增益系数会随着介质温度的增加而呈现指数上升的趋势. 关键词： 受激布里渊散射 阈值 增益系数     

Electron mobility in the linear region of an AlGaN/AlN/GaN heterostructure field-effect transistor

We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas （213EG） with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.     

不同散射机理对 Al2O3/InxGa1-xAs nMOSFET 反型沟道电子迁移率的影响

通过考虑体散射、界面电荷的库仑散射以及 Al₂O₃/In_xGa_1-xAs 界面粗糙散射等主要散射机理, 建立了以 Al₂O₃为栅介质In_xGa_1-xAs n 沟金属-氧化物-半导体场效应晶体管 (nMOSFETs) 反型沟道电子迁移率模型, 模拟结果与实验数据有好的符合. 利用该模型分析表明, 在低至中等有效电场下, 电子迁移率主要受界面电荷库仑散射的影响; 而在强场下, 电子迁移率则取决于界面粗糙度散射. 降低界面态密度, 减小 Al₂O₃/In_xGa_1-xAs 界面粗糙度, 适当提高In含量并控制沟道掺杂在合适值是提高 InGaAs nMOSFETs 反型沟道电子迁移率的主要途径. 关键词： InGaAs MOSFET 反型沟道电子迁移率 散射机理     

空间电荷限制电流法测量共混体系中空穴的迁移率

载流子迁移率测量是有机半导体材料与器件研究中的重要内容之一.以聚噻吩为电子给体材料, C₆₀的衍生物为电子受体材料,制备了一种单电荷传输器件.用空间电荷限制电流法测出了不同溶剂形成的 活性层及不同温度热处理后器件中空穴的迁移率.结果表明:器件中电荷的传输J-V曲线符合Mott-Gurney方程, 不同溶剂形成活性层中空穴具有不同的迁移率,高沸点的溶剂1, 2-二氯苯形成的活性层具有较高的空穴迁移率, 热处理有利于器件中空穴迁移率的提高.同时还进一步分析了空穴迁移率变化的原因.