Van der Waals epitaxy of ultrathin crystalline PbTe nanosheets with high near-infrared photoelectric response

Nano Research - Lead telluride (PbTe) is one of the reliable candidates for infrared (IR) optoelectronics with optimum band-gap as well as excellent photoelectric properties. Great interests had...     

Monolithic integrated resonant tunneling diode and heterostructure junction field effect transistor circuits

We have developed a simple technology for monolithic integration of resonant tunneling diodes (RTDs) and heterostructure junction-modulated field effect transistors (HJFETs). We have achieved good device performance with this technology: HJFETs had transconductances of 290 mS/mm and current densities of 310 mA/mm for a 1.5 μm gate length; RTDs had room temperature peak to valley ratios greater than 20:1 with current densities of 42 kA/cm². With this technology, we have demonstrated a monolithically integrated RTD + HJFET state holding circuit that can serve as a building block circuit for self-timed logic units. This circuit is resistor-free and operates at room temperature. The state holding circuit showed large noise margins of 1.21 V and 0.71 V, respectively, for input low and input high, for a 1.7 V input voltage swing. We have examined the transient response of the circuit and investigated the effect of circuit design parameters on propagation delay. We identify the RTD valley current as the limiting factor on propagation delay. We discuss the suitability of RTD + HJFET circuits such as our state holding circuit for highly dense integrated circuits.     

Simultaneously controlling phase,morphology and up-conversion luminescence via lanthanide doping in Bi2O3: Yb3+/Tm3+ nanoparticles

Bi₂O₃: Yb³⁺/Tm³⁺ nanoparticles with varied phase structures and morphologies were synthesized via the co-precipitation method assisted with a subsequent high-temperature calcination process. The influences of experimental parameters including dosage of urea, dopant concentration, reaction temperature and time on the crystal phase structures and morphologies of the as-prepared nanoparticles were investigated. Results revealed that the morphology, the crystal phase and the up-conversion emission of Bi₂O₃: Yb³⁺/Tm³⁺ could be simultaneously controlled by varying Yb³⁺ doping concentration. With increasing Yb³⁺ doping concentration (0-40%), the dramatic morphological evolution (nano-sheet to nano-flower to nano-sphere) and phase transition (monoclinic to tetragonal to cubic phase) were observed. Under the excitation of CW and pulse 980 nm lasers, Bi₂O₃: Yb³⁺/Tm³⁺ samples exhibited red (693 nm) and NIR (795 nm) double-band up-conversion emissions, where the increase of Yb³⁺ concentration leaded to the decreased emission intensity ratio of NIR to red (I₇₉₅/I₆₉₃) and the suppressed pulse-width-dependent up-conversion output.     

Microcomputer controlled arc oscillator for automated TIG welding

A magnetic arc oscillation system has been developed to control the fusion characteristic of arc welding. A single-pole electromagnet generates a transverse magnetic field parallel to the weld line. The weave pattern of the magnetic field, hence the bead geometry, is controlled by a custom-built computer. The applied magnetic field has a marked influence on the bead width, but less on the bead depth. Experiments also show that bead appearance is improved by magnetically oscillating the arc.     

一种无线宽带收发机载波泄漏校准和补偿技术

A carrier leakage calibration and compensation technique based on digital baseband for a wideband wireless communication transceiver is proposed. The digital baseband transmits a calibration signal, samples the signal which passes through the transmitter path and the calibration loop in the RF chip, measures the carrier leakage by analyzing the sampled data and compensates it. Compared with a self-calibration technique in the RF chip, the proposed technique saves area and power consumption for the wireless local area network （WLAN） solution. This technique has been successfully used for 802.1 In system and satisfies the requirement of the standard by achieving over 50 dB carrier leakage suppression.     

一种低功耗高速空间光调制器驱动电路

本文描述了一种新型的多量子阱空间光调制器驱动电路的设计和测试。为了解决时钟同步问题并减少功耗,我们有别于前人,将所有电路模块集成在一块芯片上。因为传统的单斜坡数模转换器无法消除电容的失配,所以我们转而采用64个列共享8位电阻串数模转换器来提供输出电压,实现0.5V至3.8V的可编程电压调控。这些数模转换器被紧密放置于6464 驱动阵列的上方力求减小失配。每个转换器消耗80uA电流,在280ns内完成一次转换。为了更快的传输速率,系统采用2级缓存,工作时钟50MHz,真刷新率达到50K帧每秒,整片功耗302mW。芯片采用0.35um CMOS工艺,面积5.5 mm7 mm。     

退火对Ge掺杂SiO2薄膜的影响

用等离子体增强化学气相淀积制备了Ge掺杂SiO2薄膜,并对薄膜进行了不同温度的退火处理。采用棱镜耦合仪、原子力显微镜和傅里叶变换红外光谱分析技术研究了不同退火温度对Ge掺杂SiO2薄膜性质的影响。通过1 100℃退火处理后,正的折射率变化量和负的体积变化量随着GeH4流量增加而增大,Ge-O-Ge键增多;而通过900℃退火处理后,折射率没有随着GeH4流量增加而增大;薄膜的表面粗糙度随着退火温度升高而降低。研究结果表明,SiO2薄膜中Ge掺杂过量,其折射率反常下降;通过1 100℃退火处理后,折射率随着GeH4流量增加而增大,折射率的增大主要是由于薄膜密实化和Ge-O-Ge键的形成。     

Morphology and defect study in low pressure MOCVD grown AlGaAs

A low pressure MOCVD system has been adopted to grow AlGaAs epitaxial layer on Si-doped or S.I. GaAs substrate by using TMA, TEG and AsH₃ as the sources.The effect of temperature on the surface morphology has been studied and a defect free surface has nearly been obtained.From EPMA analysis, at lower growth temperature (<710°C), the “whiskers” which were observed in this study are composed of a region with much less aluminum content than the surrounding normal region, but gallium and arsenic contents are nearly the same. There are few “precipitate hillock” defects on the epilayers especially under low growth temperature (<720°C), in which region, the aluminum content is greater than the surrounding region but gallium and arsenic contents are less.Raising the growth temperature (>750°C), both of “whisker defect” and “precipitate hillock” are eliminated. Very few “twin faults” defects and “bird-fault” defects on the epitaxial layers grown under high growth temperature were observed.