Temperature dependent responsivity of quantum dot infrared photodetectors

Temperature dependent behavior of the responsivity of InAs/GaAs quantum dot infrared photodetectors was investigated with detailed measurement of the current gain. The current gain varied about two orders of magnitude with 100 K temperature change. Meanwhile, the change in quantum efficiency is within a factor of 10. The dramatic change of the current gain is explained by the repulsive coulomb potential of the extra carriers in the QDs. With the measured current gain, the extra carrier number in QDs was calculated. More than one electron per QD could be captured as the dark current increases at 150 K. The extra electrons in the QDs elevated the Fermi level and changed the quantum efficiency of the QDIPs. The temperature dependence of the responsivity was qualitatively explained with the extra electrons.     

双光束组合激光辐照光导型CdS光电探测器的实验研究

为研究波段内和波段外组合激光对光导型光电探测器的辐照效应,实验采用532nm(波段内)和1319nm(波段外)双光束组合连续激光辐照光导型CdS光电探测器,分别改变两束激光的辐照功率,得到探测器的电压响应曲线。实验结果表明,光电探测器对波段内和波段外激光都有响应,但在激光开始和停止辐照瞬间探测器对两束激光的响应电压刚好相反。探测器对波段外激光的电压响应随线性工作区间内的波段内激光功率升高而增大;随着波段内激光趋于饱和,对波段外激光的响应电压近似指数级下降。分析认为,光电探测器对波段外激光的响应为光激发热载流子效应,是由自由载流子吸收激光能量产生带内跃迁引起的;波段内激光辐照影响探测器对波段外激光的吸收系数。     

基于VO2薄膜非致冷红外探测器光电响应研究

VO₂薄膜是非致冷微测辐射热红外探测器热敏电阻材料.研究中应用微电子工艺制备了VO₂溅射薄膜红外探测器,在296K的环境中测试了该探测器在不同的直流偏置、光调制频率下对873K标准黑体源8—12μm红外辐射的光电响应以及器件的噪声电压,在10和30Hz的调制频率下其响应率分别大于17kV/W和接近10kV/W.该探测器实现了探测率D大于1.0×10⁸cm (Hz)^1/2/W,热时间常量为0.011s的8—12μm非致冷 关键词： 非致冷测辐射热探测器 红外探测器 二氧化钒 薄膜     

基于像散法的线阵CCD相机检焦技术

航天立体测绘相机受卫星发射过程的振动、冲击以及复杂的空间环境的影响,相机的靶面将不同程度地偏离相机的焦平面,导致图像分辨率下降.对于测绘相机,其主点位置和主距变化量直接影响地面目标定位准确度.为了弥补利用编码器进行检焦的不足,提出了一种基于像散量的检调焦方法.该方法采用四象限光电探测器测量相机靶面变化引起的像散量,参照已标定的靶面位置与像散量之间的关系,计算出靶面偏离相机焦平面的实际大小和方向.这种检焦方法包含引起相机靶面离焦的所有因素,试验结果表明,基于像散法的测绘相机调焦机构的分辨率可达0.025 mm.     

气源MBE外延自组装GeSi量子点光致荧光研究

利用气源分子束外延设备（MBE）制作了GeSi自组装量子点样品。利用原子力显微镜（AFM）和光致荧光（PL）光谱研究了量子点的形貌和光学性质。气源MBE在较低温度下生长的量子点材料具有较高的量子点覆盖度。200K以下载流子以局域激子形式束缚在量子点中,激子束缚能约为17meV。升温至200K,载流子的输运过程发生变化。对量子点PL积分强度与温度关系曲线进行拟合得到量子点中空穴跃迁至浸润层的热激活能为129meV。     

超导纳米线单光子探测器件的制备

超导纳米线单光子探测器件(SNSPD)是超导单光子探测系统的核心器件。文中介绍了成功制备的基于5nm厚的NbN超导超薄薄膜的SNSPD器件。器件核心结构为150nm宽的纳米曲折线结构,纳米线条占空比为75%,面积为20μm×20μm。超导纳米线是利用电子束曝光(EBL)技术和反应离子刻蚀(RIE)等工艺技术制备的。所制备的SNSPD样品,在温度3.5K下的临界电流约12.9μA;在1310nm波长光波辐照,12.5μA的偏置电流下,探测效率约0.016%。     

激光辐照PC型HgCdTe探测器的实验研究

分别用连续波1.319μm激光和10.6μm激光辐照PC型HgCdTe红外探测器时,得到了不同辐照光功率密度下,探测器输出的一系列实验结果。给出了在波长为1.319μm的波段内激光辐照下PC型HgCdTe探测器的饱和阈值;用波长为10.6μm的波段外CO2激光辐照探测器时,发现了一些与波段内激光辐照探测器时大不相同的实验现象;对实验结果进行了分析。简要总结了PC型HgCdTe探测器对于波段内和波段外激光辐照的响应机制。     

Predicting future duration from present age: A critical assessment

Using a temporal version of the Copernican principle, Gott has proposed a statistical predictor of future longevity based on present age (Gott III, J. R., 1993, Nature, 363, 315) and applied the predictor to a variety of examples, including the longevity of the human species. Although Gott's proposal contains a grain of truth, it does not have the universal predictive power that he attributes to it.     

Solvent selection in ultrasonic-assisted emulsification microextraction: Comparison between high- and low-density solvents by means of novel type of extraction vessel

There are numerous published reports about dispersive liquid phase microextraction of the wide range of substances, however, till now no broadly accepted systematic and purpose oriented selection of extraction solvent has been proposed. Most works deal with the optimization of available solvents without adequate pre-consideration of properness. In this study, it is tried to compare the performances of low- and high-density solvents at the same conditions by means of novel type of extraction vessel with head and bottom conical shape. Extraction efficiencies of seven basic pharmaceutical compounds using eighteen common organic solvents were studied in this work. It was much easier to work with high-density solvents and they mostly showed better performances. This work shows that although exact predicting the performance of the solvents is multifaceted case but the pre-consideration of initial selection of solvents with attention to the physiochemical properties of the desired analytes is feasible and promising. Finally, the practicality of the method for extraction from urine and plasma samples was investigated.     

Sol–gel derived ZnO nanoparticulate films for ultraviolet photodetector (UV) applications

Zinc oxide nanoparticles based UV detector was fabricated on thermally oxidized silicon substrate. ZnO nanoparticle films were deposited using sol–gel route. The seed solution was prepared using two different solvents (methanol and isopropyl alcohol (IPA)). The surface morphology of the prepared films was characterized by FESEM. Structural characterization along with optical measurements was carried out using XRD and UV–vis spectroscopy. For the UV photo-detector, ZnO thin film prepared in IPA is selected based on their structural and optical analysis. The changes in photo-response of ZnO thin film with respect to time was studied under the dark and variable UV intensities. It was observed that the photocurrent increased with a factor of 4.82 under 1.16 mW of UV intensity. It is believe that the synthesized ZnO thin films have potential to use in the ultraviolet photo-detector applications.