LO-PHONON-ASSISTED TUNNELING IN ASYMMETRIC DOUBLE-WELL STRUCTURES WITH THICK BARRIERS

Nonresonant electron tunneling between asymmetric double quantum wells in AlxGa1-xAs/GaAs systems has been investigated by using steady-state and time-resolved photoluminescence spectra. Experimental evidence of LO-phonon-assisted tunneling through thick barriers has been obtained by enhancing excitation power densities or applying electric fields perpendicular to the well plane. LO-phonon-assisted tunneling times have also been estimated from the variation of the decay time of the narrow-well photoluminescence with applied electric fields. Our findings suggest that LO phonons in the barriers play an important role in the tunneling transfer.

CHARACTERISTICS OF THE MAGNETIC DEPOPULATION OF SUBBANDS IN VERY NARROW SYSTEMS

We present a model for electrons confined in narrow conducting channels by a parabolic well under moderate to high magnetic fields which takes into account a cutoff in the filling of the subbands. Such a cutoff gives rise to energy-separated subbands and a two-dimensional (2D) like subband depopulation, resulting in a relation between sublevel index n and inverse magnetic field B-1 such that in the high-field regime it changes over to the well-known 2D form as expected, and in the moderate field regime it shows pronounced deviation from linearity. This agrees well with the experimental results. The linear region of the n-B-1 experimental plot is believed to arise from the two dimensionality of the system. Calculations show that no resolvable 1D sublevel exists in the 0.5-mu-m-wide wire at very small magnetic fields (including zero field), which agrees qualitatively with the experimental results found in other wires that the Hall resistance, R(H), approaches its classical value B/n(e)e in this region and R(H) = 0 at B = 0, where n(e) is the electron concentration. In this model the linear and nonlinear regions in the experimental n-B-1 plot are used to extract the characteristic frequency omega-0, and the effective 2D electron concentration N(e)2D, respectively.

OPTICAL BISTABILITY IN A GAAS/GAALAS MULTI-QUANTUM-WELL (MQW) SELF-ELECTROOPTIC EFFECT DEVICE (SEED)

Based on a GaAs/GaAlAs MQW pin structure grown by a home-made MBE system, we have successfully fabricated a SEED. The optical bistability and related properties of the device under symmetric operation (S-SEED) and asymmetric operation are reported.

Resonant magnetopolaron effects due to interface phonons in GaAs/AlGaAs multiple quantum well structures

Polaron cyclotron resonance (CR) has been studied in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well structures in magnetic field up to 30 T. Large avoided-level-crossing splittings of the CR near the GaAs reststrahlen region, and smaller splittings in the region of the AlAs-like optical phonons of th AlGaAs barriers, are observed. Based on a comparison with a detailed theoretical calculation, the high frequency splitting, the magnitude of which increases with decreasing well width, is assigned to resonant polaron interactions with AlAs-like interface phonons.

Low-temperature (10 K) infrared measurement of interstitial oxygen in heavily antimony-doped silicon via wafer thinning

A new technique is reported for the rapid determination of interstitial oxygen in heavily Sb-doped silicon. This technique includes wafer thinning and low-temperature 10 K infrared measurement on highly thinned wafers. The fine structure of the interstitial oxygen absorption band around 1136 cm(-1) is obtained. Our results show that this method efficiently reduces free-carrier absorption interference, allowing a high reliability of measurement, and can be used at resistivities down to 1 x 10(-2) Omega cm for heavily Sb-doped silicon.

Total Dose Radiation-Hard 0. SOI CMOS Transistors and ASIC

This paper presents the total dose radiation performance of 0. S^m SOI CMOS devices fabricated with full dose SIMOX technology. The radiation performance is characterized by threshold voltage shifts and leakage currents of transistors and standby currents of ASIC as functions of the total dose up to 500krad(Si) .The experimental results show that the worst case threshold voltage shifts of front channels are less than 320mV for pMOS transistors under off-gate radiation bias at lMrad(Si) and less than 120mV for nMOS transistors under on-gate radiation bias. No significant radiation-induced leakage current is observed in transistors to lMrad(Si). The standby currents of ASIC are less than the specification of 5μA over the total dose range of 500krad(Si).

基于VCSEL的RCE探测器光电响应特性

对垂直腔面发射激光器（VCSEL）及由此制成的谐振增强型（RCE）光电探测器进行分析研究。激光器的I_(th) = 3 mA、η_d = 15%、λ_p = 839 nm和Δλ_(1/2) = 0.3 nm；作为探测器，光电流谱峰值响应在839 nm，响应谱线半宽2.4 nm、具有良好的波长选择特性，量子效率5%～35%(0 V～5 V)。优化设计顶镜反射率，还能得到量子效率峰值和半宽优化兼容的VCSEL基RCE光电探测器。

High power continuous-wave operation of self-organized In(Ga)As/GaAs quantum dot lasers

Quantum dot (QD) lasers are expected to have superior properties over conventional quantum well lasers due to a delta-function like density of states resulting from three dimensional quantum confinements. QD lasers can only be realized till significant improvements in uniformity of QDs with free of defects and increasing QD density as well in recent years. In this paper, we first briefly give a review on the techniques for preparing QDs, and emphasis on strain induced self-organized quantum dot growth. Secondly, self-organized In(Ga)As/GaAs, InAlAs/GaAlAs and InAs/InAlAs Qds grown on both GaAs and InP substrates with different orientations by using MBE and the Stranski-Krastanow (SK) growth mode at our labs are presented. Under optimizing the growth conditions such as growth temperature, V/III ratio, the amount of InAs, InxGa1-xAs, InxAl1-xAs coverage, the composition x etc., controlling the thickness of the strained layers, for example, just slightly larger than the critical thickness and choosing the substrate orientation or patterned substrates as well, the sheet density of ODs can reach as high as 10(11) cm(-2), and the dot size distribution is controlled to be less than 10% (see Fig. 1). Those are very important to obtain the lower threshold current density (J(th)) of the QD Laser. How to improve the dot lateral ordering and the dot vertical alignment for realizing lasing from the ground states of the QDs and further reducing the Jth Of the QD lasers are also described in detail. Thirdly based on the optimization of the band engineering design for QD laser and the structure geometry and growth conditions of QDs, a 1W continuous-wave (cw) laser operation of a single composite sheet or vertically coupled In(Ga)As quantum dots in a GaAs matrix (see Fig. 2) and a larger than 10W semiconductor laser module consisted nineteen QD laser diodes are demonstrated. The lifetime of the QD laser with an emitting wavelength around 960nm and 0.613W cw operation at room temperature is over than 3000 hrs, at this point the output power was only reduced to 0.83db. This is the best result as we know at moment. Finally the future trends and perspectives of the QD laser are also discussed.

Theoretical analysis of the relationships between hardness, elastic modulus, and the work of indentation for work-hardening materials

In our previous paper, the expanding cavity model (ECM) and Lame solution were used to obtain an analytical expression for the scale ratio between hardness (H) to reduced modulus (E-r) and unloading work (W-u) to total work (W-t) of indentation for elastic-perfectly plastic materials. In this paper, the more general work-hardening (linear and power-law) materials are studied. Our previous conclusions that this ratio depends mainly on the conical angle of indenter, holds not only for elastic perfectly-plastic materials, but also for work-hardening materials. These results were also verified by numerical simulations.

Analysis of the practical force accuracy of electromagnet-based nanoindenters

Two important factors that influence the force accuracy of the electromagnet-based nano-indenters but have not yet attracted much attention are analyzed, and a more reasonable way to estimate the force accuracy is presented in this paper. MTS Nano Indenter (R), with the characteristics of a coil suspended in a uniform magnetic field by two sets of springs acting as an actuator and force measuring unit, is used as an example. One of the two factors is the uniformity of the magnetic field. The other is the stiffness of the supporting spring. Consequently, the practical force accuracy varies considerably from test to test because it firmly depends on the working position of the coil and the displacement stroke. A reasonable estimated accuracy value is of the order of 10 degrees mu N for typical indentation tests with a 10(2) nm indentation depth or a 10 degrees mN test force. (C) 2010 Elsevier Ltd. All rights reserved.

稀有事件搜索

简单介绍了远离核奇异性质研究的科学意义,报道了稀有事件的搜索方法,以高生成额、高分离效率和高探测效率的方法搜索稀有事件。通过放射化学分离方法从天然Th中提取出镭元素,准备薄的228Raβ→-228Ac源。由60MeV/u18O离子照射天然Th靶引起的232Th-2p反应产生230Ra,通过放射化学分离方法从被照射的靶中提取出镭元素并制成薄源,经230Raβ→-230Ac得到230Ac。利用35MeV的质子束轰击ThO2粉末靶,通过232Th(p,3n)反应产生230Pa核,经用放射化学分离方法分离出Pa,并制成230Paβ→-230U测量源。用固体径迹探测器和PHGe"射线探测器记录和测量来自源中的裂变碎片(重离子)和"谱,观测到它们的!延发裂变或重离子事件,得到228Ac和230Ac的!延发裂变概率分别为(5±2)×10-12和(1.19±0.85)×10-8,230U发射22Ne相当于α衰变的分支比B=$Ne/$#为(1.3±0.8)×10-14。