Tunable spin-orbit interaction in trilayer graphene exemplified in electric-double-layer transistors

Taking advantage of ultrahigh electric field generated in electric-double-layer transistors (EDLTs), we investigated spin-orbit interaction (SOI) and its modulation in epitaxial trilayer graphene. It was found in magnetotransport that the dephasing length L(φ) and spin relaxation length L(so) of carriers can be effectively modulated with gate bias. As a direct result, SOI-induced weak antilocalization (WAL), together with a crossover from WAL to weak localization (WL), was observed at near-zero magnetic field. Interestingly, among existing localization models, only the Iordanskii-Lyanda-Geller-Pikus theory can successfully reproduce the obtained magnetoconductance well, serving as evidence for gate tuning of the weak but distinct SOI in graphene. Realization of SOI and its large tunability in the trilayer graphene EDLTs provides us with a possibility to electrically manipulate spin precession in graphene systems without ferromagnetics.     

Determination of Spin-Orbit Interaction in InAs Heterostructure

Spin-orbit interaction (SOI) gives a useful tool to control spin precession in the semiconductor without external magnetic field. The Rashba effect induced by spin-orbit interaction enables to imagine the spin field effect transistor in which the resistance modulation is achieved by precession of spins moving in a channel. The oscillatory magnetoresistance was measured to determine SOI parameter of inverted type high electron mobility transistor structure where InAs quantum well is inserted to InAlAs/InGaAs barrier layer. The band structure and electron charge distribution of the structure was calculated using WinGreen simulator. Observed SOI parameters are large enough to produce high Rashba field of about a few Tesla. The magnitude of the SOI parameter is subject to change with the InAs quantum-well thickness.      

Single electron transistor fabricated with SOI wafer

The single electron transistor (SET) is the most sensitive device for measuring the charge of electron. It has been proposed by Kane that the SET can be used for readout of calculated results in Si-based quantum computer. We fabricated the SET with SOI substrate utilizing the suspended mask of SiO₂ and Si for the purpose of using it for readout of calculation in Si-Based quantum computer. By using only the above materials for the mask, high temperature processes including ion implantation and activation annealing could be possible and it was never achieved in conventional methods with the suspended mask with photoresist. First, the suspended mask with enough undercut in SOI was made by removing the box oxide of SOI wafer combining with pattern delineation by electron beam lithography, anisotropically reactive ion etching and isotropic wet etching. After forming the suspended mask, Al films were evaporated from two different angles to make an overlap just below the bridge, resulting in completing the SET in the undercut region possible to measure the electron spin. After making the Al/Al₂O₃/Al SET, we measured the I–V characteristic between source and drain at 1.8 K. The Coulomb blockade and the Coulomb oscillation were observed.     

Slot optical waveguide usage in forming passive optical devices

We have reviewed the work on SOI slot optical waveguides followed by our work. In a slot waveguide structure, light can be confined in a low index slot guarded by high index slabs. Slot structures are being used in forming complex structures; such as ring resonator circuits. The increased round trip in ring resonator circuits signifies the importance of dispersion calculations. We did analytical and numerical investigations of slot structures' dispersion characteristics. Our dispersion tuned slot structures can help in reducing the dispersion effects on optical signal, which will in turn improve the efficiency of light-on-chip circuits. Since the advent of slot optical waveguides, SOI based slot optical waveguides have been under consideration. It has been found that glass based slot optical waveguide structures with relatively low refractive index contrast ratio can also play an important role in forming complex nano-size optical devices. We made use of power confined inside low index slot regions for a double slot structure. Opto-mechanical sensors have been proposed based upon: (a) variation in power confined inside low index slot region due to the movement of central high index slab under the action of external force (temperature, pressure, humidity, etc). vide Chinese Patent No. ZL 200710176770.1, 2007 (b) variation in power confined inside low refractive index slot regions due to movement of both slots under the action of external force (temperature, pressure, humidity, etc).     

Analysis of the birefringence of a silicon-on-insulator rib waveguide

A detailed analysis of the polarization characteristics (birefringence) of a silicon-on-insulator (SOI) rib waveguide is given. The fundamental TE- and TM-polarized modes of the SOI rib waveguide are calculated by a semivectorial finite-difference method. The rib width and the slab height of the SOI rib waveguide are normalized with respect to the total height of the silicon layer. A general relation between the two normalized parameters for a nonbirefringent SOI rib waveguide is obtained. According to this relation a nonbirefringent SOI rib waveguide can easily be designed. The fabrication tolerance for a nonbirefringent SOI rib waveguide is also analyzed, revealing that the tolerance can be increased by use of a larger total height of the silicon layer.     

Improvement in thickness uniformity of thick SOI by numerically controlled local wet etching

Silicon-on-insulator (SOI) wafers are promising semiconductor materials for high-speed LSIs, low-power-consumption electric devices and micro electro mechanical systems (MEMS). The thickness distribution of an SOI causes the variation of threshold voltage in electronic devices manufactured on the SOI wafer. The thickness distribution of a thin SOI, which is manufactured by applying a smart cut technique, is comparatively uniform. On the other hand, a thick SOI has a large thickness distribution because a bonded wafer is thinned by conventional grinding and polishing. For a thick SOI wafer with a thickness of 1 microm, it is required that the tolerance of thickness variation is less than 50 nm. However, improving the thickness uniformity of a thick SOI layer to a tolerance of +/- 5% is difficult by conventional machining because of the fundamental limitations of these techniques. We have developed numerically controlled local wet etching (NC-LWE) technique as a novel deterministic subaperture figuring and finishing technique, which utilizes a localized chemical reaction between the etchant and the surface of the workpiece. We demonstrated an improvement in the thickness distribution of a thick SOI by NC-LWE using an HF/HNO3 mixture, and thickness variation improved from 480 nm to 200 nm within a diameter of 170 mm.     

Illumination system design for a three-aspherical-mirror projection camera for extreme-ultraviolet lithography

A scanning critical illumination system is designed to couple a synchrotron radiation source to a three-aspherical-mirror imaging system for extreme ultraviolet lithography. A static illumination area of H x V = 8 mm x 3 mm (where H is horizontal and V is vertical) can be obtained. Uniform intensity distribution and a large ring field of H x V = 150 mm x 3 mm can be achieved by scanning of the mirror of the condenser. The coherence factor (varsigma) of this illumination system is ~0.6, with the same beam divergence in both the horizontal and the vertical directions. We describe the performance of the imaging optics at varsigma = 0.6 to confirm that the illumination optics can meet the requirements for three-aspherical-mirror imaging optics with a feature size of 0.06 mum.     

Fabrication and characterization of micromachined high-frequency tonpilz transducers derived by PZT thick films

Miniaturized tonpilz transducers are potentially useful for ultrasonic imaging in the 10 to 100 MHz frequency range due to their higher efficiency and output capabilities. In this work, 4 to 10-microm thick piezoelectric thin films were used as the active element in the construction of miniaturized tonpilz structures. The tonpilz stack consisted of silver/lead zirconate titanate (PZT)/lanthanum nickelate (LaNiO3)/silicon on insulator (SOI) substrates. First, conductive LaNiO3 thin films, approximately 300 nm in thickness, were grown on SOI substrates by a metalorganic decomposition (MOD) method. The room temperature resistivity of the LaNiO3 was 6.5 x 10(-6) omega x m. Randomly oriented PZT (52/48) films up to 7-microm thick were then deposited using a sol-gel process on the LaNiO3-coated SOI substrates. The PZT films with LaNiO3 bottom electrodes showed good dielectric and ferroelectric properties. The relative dielectric permittivity (at 1 kHz) was about 1030. The remanent polarization of PZT films was larger than 26 microC/cm2. The effective transverse piezoelectric e31,f coefficient of PZT thick films was about -6.5 C/m2 when poled at -75 kV/cm for 15 minutes at room temperature. Enhanced piezoelectric properties were obtained on poling the PZT films at higher temperatures. A silver layer about 40-microm thick was prepared by silver powder dispersed in epoxy and deposited onto the PZT film to form the tail mass of the tonpilz structure. The top layers of this wafer were subsequently diced with a saw, and the structure was bonded to a second wafer. The original silicon carrier wafer was polished and etched using a Xenon difluoride (XeF2) etching system. The resulting structures showed good piezoelectric activity. This process flow should enable integration of the piezoelectric elements with drive/receive electronics.     

Cross-linkable bromo-fluorinated poly(arylene ether ketone)s for photonic device applications

A series of novel cross-linkable bromo-fluorinated poly(arylene ether ketone)s have been synthesized and used to fabricate photonic devices. The polymers, prepared by polycondensation reactions of decafluorobenzophenone with mixtures of bisphenols in different ratios, exhibit excellent solubility in common organic solvents and can be easily cast into optical-quality thin films by spin coating. The materials are thermally stable with decomposition temperatures (Td, 5% weight loss) over 450 degrees C and have high glass transition temperatures (Tg) in the range of 164 degrees C-178 degrees C. By controlling the bromine content of the polymers, the refractive index can be precisely controlled over a range as wide as 0.07. The material has excellent design flexibility, low optical loss (0.4-0.6 dB/cm at 1550 nm), a low birefringence (2-3 x 10(-3)), and is suitable for use in wavelength sensitive photonic devices based on arrayed waveguide gratings.     

Hybrid silicon integration

An overview is presented of the hybrid AlGaInAs-silicon platform that enables wafer level integration of III-V optoelectronic devices with silicon photonic devices based on silicon-on-insulator (SOI). Wafer bonding AlGaInAs quantum wells to an SOI wafer allows large scale hybrid integration without any critical alignment steps. Discrete hybrid silicon optical amplifiers, lasers and photodetectors are described, and the integration of a ring laser with on-chip and photo-detector and amplified spontaneous emission (ASE) seed to enable unidirectional lasing.     

Heat Transfer in Fast Linear Annealing for Direct Bonding of SOI Wafer Pairs

A novel silicon-on-insulator (SOI) manufacturing method, the fast linear annealing (FLA) method, is proposed. In the fast linear annealing method, a halogen lamp moves with a constant speed above a silicon wafer pair prebonded by the hydrogen interaction. In order to optimize the processing parameters such as the initial heat treatment time and the moving speed of the halogen lamp, bonding strengths were measured when the moving speed varies in the range of 0.05–0.5 mm · s⁻¹. The temperature distribution of SOI is analyzed numerically by using a finite difference method. The SOI is modeled two-dimensionally, and the alternate direction implicit (ADI) technique is used for the calculation of the temperature. The calculation results show that the SOI reaches a steady-state temperature distribution in an elapsed time of 380 s of halogen lamp irradiation. The maximum temperature of SOI does not vary significantly as the moving speed of the halogen lamp increases. These results agree with the measurement results, which show that the bonding strength from the high-speed anneal (0.5 mm · s⁻¹) was of similar strength to that from the slow speed (0.05 mm · s⁻¹) process.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

基于薄膜SOI材料的GaN外延生长应力释放机制

本文研究了SOI衬底上采用MOCVD方法生长GaN材料的应力释放机制.采用SIMOX工艺制备的具有薄膜顶层硅的SOI材料作为外延生长的衬底材料,采用MOSS在位检测系统以及拉曼测试作为GaN内部应力的表征手段.结果表明,SOI材料对硅基GaN异质外延中的晶格失配应力和热应力的释放都有显著作用.薄膜SOI材料通过顶层硅与外延层的界面滑移,将一部分晶格失配应力通过界面的滑移释放,并且通过柔性薄膜顶层硅自身的应力吸收作用,将一部分热失配应力转移到衬底,从而有效地降低了GaN外延层的张应力.     

Precision stabilization of the optical frequency in a large ring laser gyroscope

Pressure-induced fractional changes of 10(-7) in the geometry of a large He-Ne ring laser gyroscope induce backscatter phase changes and thus a fractional pulling of the Sagnac frequency of ~5 x 10(-3). To counter this, the optical frequency was stabilized against an iodine-stabilized laser with a high-finesse Fabry-Perot interferometer and piezoelectric control of the ring perimeter. This scheme, although limited in principle by residual geometric asymmetry and in practice by low beam powers (10 pW), stabilized the perimeter to 2.4 nm (6 x 10(-10) or 300 kHz for the optical frequency) and the Sagnac frequency to 100 parts per million over several days.     

Magnetic proximity effect as a pathway to spintronic applications of topological insulators

Spin-based electronics in topological insulators (TIs) is favored by the long spin coherence(1,2) and consequently fault-tolerant information storage. Magnetically doped TIs are ferromagnetic up to 13 K,(3) well below any practical operating condition. Here we demonstrate that the long-range ferromagnetism at ambient temperature can be induced in Bi(2-x)Mn(x)Te(3) by the magnetic proximity effect through deposited Fe overlayer. This result opens a new path to interface-controlled ferromagnetism in TI-based spintronic devices.     

Diethynylbenzene-based liquid crystalline semiconductor for solution-processable organic thin-film transistors

We report here the synthesis and characterization of novel diethynylbenzene-based liquid crystalline semiconductor (P1) for organic thin-film transistors (OTFTs). Compound P1 was synthesized by the Sonogashira coupling reaction between 2-bromo-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene and 1,4-bis(dodecyloxy)-2,5-diethynylbenzene. Top contact OTFTs were fabricated by spin casting with 2 wt% solution of P1 in chloroform and their best performance, which exhibited a hole mobility of 4.5 x 10(-5) cm2/Vs, was showed after annealing of the films at liquid crystalline temperature. Time-of-flight (TOF) mobility measured at liquid crystalline phase was observed to be 1.5 x 10(-6) cm2/Vs for both positive and negative carriers. These results indicate that the liquid crystallinity helps to improve the molecular packing and enhance charge mobility for P1. These advantages can be applicable to design and construct solution-processable OTFT materials for electronic applications.     

Non-linear Spin Waves on Topological Defects of Texture in Superfluid 3He-B

We have observed non-linear behaviour of stationary spin waves localised on textural topological defects. We can explain our results in the framework of the Schrödinger equation with feedback. The new method gives us the ability to see many topological defects, which are undistinguished by traditional methods of NMR. We have found that some of the non-linear spin wave modes can be responsible for the extremely long lived induction decay signals called Persistent signals.     

Molecular modulation of conductivity on H-terminated silicon-on-insulator substrates

The adsorption of a range of molecular species (water, pyridine, and ammonia) is found to reversibly modulate the conductivity of hydrogen-terminated silicon-on-insulator (H-SOI) substrates. Simultaneous sheet-resistance and Hall-effect measurements on moderately doped (10(15) cm(-3)) n- and p-type H-SOI samples mounted in a vacuum system are used to monitor the effect of gas exposure in the Torr range on the electrical-transport properties of these substrates. Reversible physisorption of "hole-trapping" species, such as pyridine (C(5)H(5)N) and ammonia (NH(3)) produces highly conductive minority-carrier channels (inversion) on p-type substrates, mimicking the action of a metallic gate in a field-effect transistor. The adsorption of these same molecules on n-type SOI induces strong electron-accumulation layers. Minority/majority channels are also formed upon controlled exposure to water vapor. These observations can be explained by a classical band-bending model, which considers the adsorbates as the source of a uniform surface charge ranging from +10(11) to +10(12)q cm(-2). These results demonstrate the utility of DC transport measurements of SOI platforms for studies of molecular adsorption and charge-transfer effects at semiconductor surfaces.     

Fano and Dicke effects in a double Rashba-ring system

The electronic transport in a system of two quantum rings side-coupled to a quantum wire is studied via a single-band tunneling tight-binding Hamiltonian. We derived analytical expressions for the conductance and spin polarization when the rings are threaded by magnetic fluxes with Rashba spin-orbit interaction. We show that by using the Fano and Dicke effects this system can be used as an efficient spin filter even for small spin-orbit interaction and small values of magnetic fluxes. We compare the spin-dependent polarization of this design and the polarization obtained with one ring side-coupled to a quantum ring. As a main result, we find better spin polarization capabilities as compared to the one-ring design.     

Lateral Shifts for Spin Electrons in a Hybrid Magnetic-Electric-Barrier Nanostructure Modulated by Spin-Orbit Couplings

We theoretically investigate how to modulate spin-dependent lateral shifts by the spin-orbit coupling (SOC) in a hybrid magnetic-electric-barrier (MEB) nanostructure, which can be experimentally realized by depositing a ferromagnetic (FM) stripe and a Schottky metal (SM) stripe on the top and bottom of the semiconductor heterostructure, respectively. Two kinds of ROCs, Rashba SOC (RSOC) and Dresselhaus SOC (DSOC), are taken into account fully. The Schrödinger equation of the spin electron in the hybrid MEB nanostructure is exactly solved by using the improved transfer-matrix method (ITMM), and the lateral shift and its spin polarization are numerically calculated with the help of the stationary phase method (SPM). Theoretical analysis indicates that the spin polarization effect in the lateral shift still exists in the hybrid MEB nanostructure when the SOCs are considered. Numerical simulations show that both magnitude and sign of the spin polarization effect in lateral shifts vary strongly with the strengths of RSOC and DSOC. These interesting features may offer an effective means to control the behavior of spin-polarized electrons in the semiconductor nanostructure, and such a hybrid MEB nanostructure serves as a SOC-manipulable spatial spin splitter for spintronic applications.     

Generation of chaotic microwave pulses with the help of passive synchronization of spin wave self-modulation frequencies in self-oscillatory ring systems

Passive synchronization (PS) of spin wave self-modulation frequencies of a chaotic microwave signal has been observed for the first time in a self-oscillatory ring system involving a nonlinear passive element with saturable absorption. The development of PS led to the generation of a periodic train of chaotic microwave pulses with an off/duty ratio exceeding 20. It is established that the repetition period of chaotic microwave pulses can be controlled by changing gain in the ring system.