Field dependence of mobility in Al0.2Ga0.8As/GaAs heterojunctions at very low fields

Multiple-period (Al, Ga)As/GaAs modulation doped heterojunction structures have been grown with molecular beam epitaxy. Electron mobilities of about 200 000 cm2/Vs at 10 K and 90000 cm2/Vs at 77 K with associated sheet carrier concentrations of about 2×1012 cm?2 have been observed. The current parallel to the interfaces for low electric fields was examined as a function of lattice temperature. The electron mobility has been observed to be strongly dependent on the strength of the electric field, and hot electron effects were observable at a field as low as 10 V/cm. To our knowledge this is the first report of hot electron phenomena in GaAs at such small fields.     

CO2laser annealing of Si3N4, Nb2O5, and Ta2O5thin-film optical waveguides to achieve scattering loss reduction

Significant reductions in the optical scattering losses of Si3N4, Nb2O5, and Ta2O5waveguides fabricated on SiO2/Si substrates have been measured following CO2laser annealing. The largest improvements were observed for Si3N4waveguides, where waveguide attenuation values of about 6.0 dB/cm before laser annealing were reduced to as low as 0.1 dB/cm afterwards. An improvement of more than an order of magnitude was obtained for a Nb2O5waveguide upon laser annealing, the attenuation coefficient decreasing from 7.4 to 0.6 dB/cm. In the case of one Nb2O5waveguide no improvement was obtained upon laser annealing. The attenuation coefficient of a reactively sputtered Ta2O5waveguide was found to decrease from 1.3 dB/cm before laser annealing to 0.4 dB/cm afterwards. In the case of a thermally oxidized Ta2O5waveguide a small initial improvement in waveguide attenuation was followed by degradation upon further laser annealing.     

Fabrication of high-performance InGaAsN ridge waveguide lasers with pulsed anodic oxidation

We have demonstrated high-performance InGaAsN triple-quantum-well ridge waveguide (RWG) lasers fabricated using pulsed anodic oxidation. The lowest threshold current density of 675 A/cm/sup 2/ was obtained from a P-side-down bonded InGaAsN laser, with cavity length of 1600 /spl mu/m and contact ridge width of 10 /spl mu/m. The emission wavelength is 1295.1 nm. The transparency current density from a batch of unbonded InGaAsN RWG lasers was 397 A/cm/sup 2/ (equivalent to 132 A/cm/sup 2/ per well). High characteristic temperature of 138 K was also achieved from the bonded 10/spl times/1600-/spl mu/m/sup 2/ InGaAsN laser.     

SiO2/native double-gate InSb MOSFETs

An InSb MOS double-gate structure formed by a novel thermal oxidation method has been investigated. C/V characteristics showed a sharp change and no hysteresis. Both n-channel and p-channel MOSFETs have been successfully operated. The effective mobility at 77 K was approximately 7800 cm2/Vs for the n-channel and 300 cm2/Vs for the p-channel.     

Cubic paraelectric (nonferroelectric) perovskite PLT thin filmswith high permittivity for ULSI DRAMs and decoupling capacitors

Polycrystalline paraelectric perovskite thin films in the Pb-La-Ti-O or PLT (28 mol.% La) system have been studied. Thin (0.5-μm) films were integrated onto 3-in Pt/Ti/SiO₂/(100) Si wafers by the sol-gel processing technique. Low-field dielectric measurements yielded dielectric permittivity and loss tangent of 1400 and 0.015, respectively, while high-field Sawyer-Tower measurements (P-E) showed linear behavior up to 40 kV/cm, which approached saturation at 200 kV/cm. Pulse charging transient and current-voltage measurements indicated a high charge storage density (15.8 μC/cm²) and low leakage current density (0.50 μA/cm²) under a field of 200 kV/cm. The charging time for a 1-μm² PLT capacitor at 200 kV/cm was estimated to be 0.1 ns. The preliminary data demonstrate that paraelectric PLT thin films have excellent potential for use in ULSI DRAMs and as decoupling capacitors     

Tm激光与角膜作用的热效应模拟

激光角膜热成形技术(LTK)在矫正远视临床中占有重要的应用前景。为了了解铥激光与角膜组织热相互作用中激光参数和角膜光学及热物性参数对温度场分布的影响,选取50W/cm2,55W/cm2,60W/cm2三种功率密度,1s、2s、3s三种作用时间,用有限元方法模拟了激光作用下角膜组织内温度场的分布。模拟结果表明激光有效穿透深度与激光功率密度和时间都是正向相关,而与能量密度的正向相关性较差;激光作用时间越长,角膜组织中的温度梯度越小。模拟得到激光功率密度50W/cm2作用时间1s适合于LTK。     

Lateral RESURF MOSFET fabricated on 4H-SiC(0001/sup ~/) C-face

Lateral reduced surface field (RESURF) metal-oxide-semiconductor field-effect transistors (MOSFETs) have been fabricated on 4H-SiC(0001/sup ~/) carbon face (C-face) substrates. The channel mobility of a lateral test MOSFET on a C-face was 41 cm/sup 2//V/spl middot/s, which was much higher than 5 cm/sup 2//V/spl middot/s for that on a Si-face. The specific on-resistance of the lateral RESURF MOSFET on a C-face was 79/spl Omega/ /spl middot/ cm/sup 2/, at a gate voltage of 25 V and drain voltage of 1 V. The breakdown voltage was 460 V, which was 79% of the designed breakdown voltage of 600 V. We measured the temperature dependence of R/sub on, sp/ for the RESURF MOSFET on the C-face. The R/sub on, sp/ increased with the increase in temperature.     

High mobility NMOSFET structure with high-/spl kappa/ dielectric

High-/spl kappa/ NMOSFET structures designed for enhancement mode operation have been fabricated with mobilities exceeding 6000 cm/sup 2//Vs. The NMOSFET structures which have been grown by molecular beam epitaxy on 3-in semi-insulating GaAs substrate comprise a 10 nm strained InGaAs channel layer and a high-/spl kappa/ dielectric layer (/spl kappa//spl cong/20). Electron mobilities of >6000 and 3822 cm/sup 2//Vs have been measured for sheet carrier concentrations n/sub s/ of 2-3/spl times/10/sup 12/ and /spl cong/5.85/spl times/10/sup 12/ cm/sup -2/, respectively. Sheet resistivities as low as 280 /spl Omega//sq. have been obtained.     

Electrical characteristics of silicon MOS structure formed by a novel low-temperature thermal oxidation method

Electrical characteristics of the native silicon-dioxide layer and its interface formed by a novel low-temperature thermal oxidation method have been evaluated. The resistivity and breakdown field strength were more than 1014 ?cm and 4 MV/cm, respectively. The interface state density had a V-shaped distribution form and its minimum value was about 1011 cm2 eV.     

Fabrication of 4H-SiC n-channel IGBTs with ultra high blocking voltage

Owing to the conductivity modulation of silicon carbide (SiC) bipolar devices,n-channel insulated gate bipolar transistors (n-IGBTs) have a significant advantage over metal oxide semiconductor field effect transistors (MOSFETs) in ultra high voltage (UHV) applications.In this paper,backside grinding and laser annealing process were carried out to fabricate 4H-SiC n-IGBTs.The thickness of a drift layer was 120 μm,which was designed for a blocking voltage of 13 kV.The n-IGBTs carried a collector current density of 24 A/cm2 at a power dissipation of 300 W/cm2 when the gate voltage was 20 V,with a differential specific on-resistance of 140 mΩ·cm2.     

分子束外延AlGaN/GaN异质结场效应晶体管材料

用自组装的氨源分子束外延 (NH3-MBE)系统和射频等离子体辅助分子束外延 (PA-MBE)系统在 C面蓝宝石衬底上外延了优质 Ga N以及 Al Ga N/Ga N二维电子气材料。Ga N膜 (1 .2 μm厚 )室温电子迁移率达3 0 0 cm2 /V· s,背景电子浓度低至 2× 1 0 1 7cm- 3。双晶 X射线衍射 (0 0 0 2 )摇摆曲线半高宽为 6arcmin。 Al Ga N/Ga N二维电子气材料最高的室温和 77K二维电子气电子迁移率分别为 73 0 cm2 /V·s和 1 2 0 0 cm2 /V· s,相应的电子面密度分别是 7.6× 1 0 1 2 cm- 2和 7.1× 1 0 1 2 cm- 2 ;用所外延的 Al Ga N/Ga N二维电子气材料制备出了性能良好的 Al Ga N/Ga N HFET(异质结场效应晶体管 ) ,室温跨导为 5 0 m S/mm(栅长 1 μm) ,截止频率达 1 3 GHz(栅长 0 .5μm)。该器件在 3 0 0°C出现明显的并联电导 ,这可能是材料中的深中心在高温被激活所致     

Broadening of the RF Power-Density Window for Calcium-ion Efflux from Brain Tissue

Blackman et al. [1], [2] have reported enhanced efflux of calcium ions from chicken forebrains, exposed in vitro in a 50 ?stripline to 147 MHz radiation, modulated sinusoidally at 16 Hz. When the spacing between the sample tubes was 3.8 cm on center, enhancement occurred at an incident power density of 0.83 mW/cm2, but not at 0.11, 0.5S, 1.11, or 1.38 mW/cm2. When the spacing between sample tubes was reduced to 1.9 cm, significant enhanced efflux was observed at incident power densities of 0.55, 0.83, 1.11, and 1.38 mW/cm2. This broadening of the effective power-density range is explained herein by calculations which show that the more closely spaced samples interact electrically in a way that both lowers and broadens the range of spatial variation-of absorbed power density (MW/cm3) within the sample for a given incident power density (mW/cm2). Electrical coupling among the samples allows several different values of incident power to yield exactly the same value of power absorbed at given points within the brain sample. Because the absorbed power density must be directly related to the power that interacts with the brain to enhance the efflux of calcium ions, the electromagnetic conditions for efflux enhancement in coupled and uncoupled brains are the same if the absorbed power density is the same. Ranges of absorbed power density are identified that could be effective in enhancing the efflux of calcium ions from the brain tissue.     

Thermographic and Behavioral Studies of Rats in the Near Field of 918-MHz Radiations

Patterns of thermalized energy of rat carcasses exposed to 918-MHz CW radiation in the near zone have been determined using a computerized thermograph. Peak absorption of energy in the body was estimated to be 0.9 W/kg per mW/cm/sup 2/ of incident energy. Operant responses of irradiated rats to schedules of fixed-ratio (food) reinforcement under the same conditions as the dosimetric test were observed to occur at averaged power densities of 30-40 mW/cm/sup 2/. This range of densities corresponds to absorbed peaks of energy of 27-36 W/kg. No change in behavior was observed for incident power densities and peaks of absorbed energy to 20-30 mW/cm/sup 2/ and to 18-27 W/kg, respectively, and all changes at higher values were reversible.     

High-mobility selectively doped GaAs/GaAlAs structures grown by low-pressure OM-VPE

We report the growth of high-quality selectively doped GaAs/GaAlAs heterostructures grown by OM-VPE. Electron mobilities as high as 162000 cm2V?1s?1 have been obtained at 2 K. The sheet carrier concentration was varied between 5 × 1011 cm?2 and 1.5 × 1012 cm?2 by changing the `spacer? thickness and the doping level in the n-type GaAlAs.     

红外宽频吸收硅基复合气凝胶的制备及表征

以正硅酸乙酯为硅源,采用酸碱两步催化法经过溶胶-凝胶和冷冻干燥制备出SiO2气凝胶基材,并在凝胶老化过程中添加三乙胺盐酸盐得到兼具中远红外吸收特性的硅基复合气凝胶。利用X射线衍射、扫描电子显微镜、氮吸附-脱附和傅里叶红外吸收光谱对气凝胶的结构和性能进行了表征。结果表明:胺盐在硅气凝胶网络结构中穿插结晶;基材的比表面积、最大孔容和平均孔径分别为524.5 m2/g、1.2 cm3/g和9.2 nm,复合材料的比表面积、最大孔容和平均孔径分别为37.93~138.7 m2/g、0.08~0.28 cm3/g和7.1~8.8 nm;基材和复合气凝胶的表观密度分别为0.25 g/cm3和0.35~0.51 g/cm3;复合气凝胶在中远红外窗口具有宽频吸收的特性,且随着三乙胺盐酸盐含量的增加,中红外相对吸收强度成比例增强。     

InP基功率HEMT结构材料分子束外延生长研究

从 3个层面研究了分子束外延 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P功率 HEMT结构材料生长技术。首先 ,通过观察生长过程的高能电子衍射 (RHEED)图谱 ,确立了 Ga0 .47In0 .53As/ In P结构表面层的 MBE RHEED衍射工艺相图 ,据此生长的单层 Si-doped Ga0 .47In0 .53As(40 0 nm) / In P室温迁移率可达 6960 cm2 / V· s及电子浓度 1 .3 3 E1 7cm- 3。其次 ,经过优化结构参数 ,低噪声 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P HEMT结构材料的 Hall参数达到μ30 0 K≥ 1 0 0 0 0 cm2 / V· s、2 DEG≥ 2 .5 E1 2 cm- 2 。最后 ,在此基础之上 ,降低 spacer的厚度、在 Ga0 .47In0 .53As沟道内插入 Si平面掺杂层并增加势垒层的掺杂浓度获得了功率 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In PHEMT结构材料 ,其 Hall参数达到μ30 0 K≥ 80 0 0 cm2 / V· s、2 DEG≥ 4 .0 E1 2 cm- 2 。     

红外宽频吸收硅基复合气凝胶的制备及表征

以正硅酸乙酯为硅源,采用酸碱两步催化法经过溶胶-凝胶和冷冻干燥制备出SiO2气凝胶基材,并在凝胶老化过程中添加三乙胺盐酸盐得到兼具中远红外吸收特性的硅基复合气凝胶。利用X射线衍射、扫描电子显微镜、氮吸附-脱附和傅里叶红外吸收光谱对气凝胶的结构和性能进行了表征。结果表明:胺盐在硅气凝胶网络结构中穿插结晶;基材的比表面积、最大孔容和平均孔径分别为524.5 m2/g、1.2 cm3/g和9.2 nm,复合材料的比表面积、最大孔容和平均孔径分别为37.93~138.7 m2/g、0.08~0.28 cm3/g和7.1~8.8 nm;基材和复合气凝胶的表观密度分别为0.25 g/cm3和0.35~0.51 g/cm3;复合气凝胶在中远红外窗口具有宽频吸收的特性,且三乙胺盐酸盐含量的增加,中红外相对吸收强度成比例增强。     

SBT铁电薄膜及其脉冲准分子激光制备

采用脉冲准分子激光沉积法在Ｐｔ／Ｔｉ／ＳｉＯ２／Ｓｉ衬底上成功地制备了ＳＢＴ铁电薄膜，发现存在一个最佳沉积衬底温度约为４５０℃。在该温度下沉积的ＳＢＴ薄膜具有较饱和的方形电滞回线，其剩余极化Ｐｒ和矫顽电场Ｅｃ分别为８．４μＣ／ｃｍ２和５７ｋＶ／ｃｍ。     

Electrical profiles from zinc implanted GaAs

Hole concentration and mobility profiles have been measured for 1015Zn+/cm2 implanted into GaAs at room temperature. After annealing at 800°C the peak hole concentration for a 60 keV implant was in excess of 1019 holes/cm3 and decreased with increasing energy up to 450 KeV.     

Au/PZT/BIT/p-Si结构铁电 存储二极管I-V 特性

采用脉冲激光沉积方法（PLD）制备了Au/PZT/BIT/p-Si多层结构铁电存储二极管.对铁电存储二极管的P-E电滞回线、I-V特性曲线分别进行了测试与分析,并对其导电行为及基于I-V特性回滞现象的存储机理进行了讨论.实验表明,所制备的多层铁电薄膜具有较高的剩余极化（27μC/cm2）和较低的矫顽场（48kV/cm）,BIT铁电层有助于缓解PZT与Si衬底之间的界面反应和互扩散,减少界面态,与Au/PZT/p-Si结构相比,漏电流密度降低近两个数量级,I-V特性曲线回滞窗口明显增大.