非对称HALO-LDD掺杂石墨烯纳米条带场效应管的电学特性研究(英文)

随着器件沟道尺寸的不断缩小,短沟道效应(SCE)和漏致势垒降低效应(DIBL)对常规类MOSFET结构的石墨烯纳米条带场效应管(GNRFET)影响变大,从而引起器件性能下降。文中提出了一种新型采用非对称HALO-LDD掺杂结构的GNRFET,其能够有效抑制器件中SCE和DIBL,改善器件性能。并采用一种量子力学模型研究GNRFET的电学特性,该模型基于二维NEGF(非平衡格林函数)方程和Poisson方程自洽全量子数值解。结合器件的工作原理,研究了GNRFET的电学特性和器件结构尺寸效应,通过与采用其他掺杂结构的GNRFET的电学特性对比分析,发现这种掺杂结构的石墨烯纳米条带场效应管具有更低的泄漏电流、更低的亚阈值斜率和DIBL以     

Ultraviolet detectors based on epitaxial ZnO films grown by MOCVD

High-quality zinc oxide (ZnO) films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range of 350°C to 600°C. In-situ nitrogen compensation doping was performed using NH₃. Microstructural and optical properties of the films, as well as the N-doping effects, were studied. The metal-semiconductor-metal ultraviolet sensitive photodetectors were fabricated on N-doped epitaxial ZnO films. The detector showed fast photoresponse, with a rise time of 1 μs and a fall time of 1.5 μs. Low-frequency photoresponsivity, on the order of 400 A/W at 5 V bias, was obtained.     

Photoluminescence in n and p modulation-doped GaInNAs/GaAs quantum wells

Experimental results concerning the steady-state photoluminescence (PL) studies in n and p modulation doped and undoped GaInNAs/GaAs quantum wells are presented. The effects of modulation, type of doping and nitrogen concentration on the PL and the temperature dependence of the band gap, carrier localization and non-radiative recombination are investigated. Increasing the nitrogen composition decreases energy band gap as expected. The n-type modulation doping eliminates most of the defect-related effects and blue shifts the energy band gap. However, the p-type doping gives rise to additional features in the PL spectra and red shifts energy band gap further compared to the n-type-doped material.     

一种渐变掺杂型pin光探测器的高速响应性能研究

高速光探测器是高速光纤通信系统和网络中的关键器件,它要求光探测器具有宽的频率响应带宽和高量子效率。垂直入光型pin光探测器的高速性能和量子效率均受到吸收层厚度的限制。为了改善其高速性能,采用InGaAsP材料作为吸收层以及限制层渐变掺杂的方法,对垂直入光型pin光探测器的高速响应性能进行了理论研究和仿真,结果表明,高速响应达到了40GHz。与不采用渐变掺杂浓度的同种结构光探测器相比,高速响应性能显著提高。     

在NPB中掺杂Alq_3改善有机电致发光器件的性能

在空穴传输层N,N′-diphenyl-N,N′-bis-1-naphthyl-(1,1′-biphenyl)-4,4′-diamine(NPB)中掺杂电子传输材料Aluminium-tris-8-hydroxy-quinoline(Alq3)制备了有机电致发光器件。当掺杂浓度低于5%时器件仍为蓝光发射,但与同等结构没有掺杂的器件相比,蓝光器件的亮度提高了近20%,达到了12460cd/m2,外量子效率提高了15.5%。随着掺杂浓度的增加,光谱发生了从蓝光到绿光的红移,这种掺杂方案能够改善空穴和电子的注入平衡,使得空穴和电子在发光层中能够有效地复合,器件的色度、亮度和效率都有了相应的改变。     

Quantitative oxygen measurements in OMVPE Al x Ga1−x As grown by methyl precursors

Oxygen has always been considered to be a major contaminant in the organo-metallic vapor phase epitaxy (OMVPE) of Al _x Ga_1−x As. Oxygen incorporation has been invoked as a contributor to low luminescence efficiency, dopant compensation and degradation of surface morphology among other deleterious effects. This study presents quantitative measurements of oxygen concentration in nominally high purity Al _x Ga_1−x As. The oxygen concentration was measured as a function of alloy composition, growth temperature, andV/III ratio. Quantitative secondary ion mass spectroscopy (SIMS) measurements were used to determine the oxygen content as well as the carbon concentration in the film. The oxygen concentration increases with decreased growth temperature and V/III ratio while increasing superlinearly with Al content in the epitaxial layer.     

0.7CaTiO_3-0.3(La_xNd_(1–x))AlO_3微波介质陶瓷的研究

利用传统固相反应法制备了具有不同LaAlO3含量的0.7CaTiO3-0.3(LaxNd1–x)AlO3(以下简称CTLNA)系微波介质陶瓷,研究了所制CTLNA陶瓷的微观结构和微波介电性能。结果表明,用x=0.5的La3+取代Nd3+能有效促进样品晶粒的均匀分布,降低样品的气孔率。少量添加SrTiO3能进一步增加样品的致密度,提高CTLNA系微波陶瓷的介电性能。经原料组分及工艺优化,制备的0.7(Sr0.01Ca0.99)TiO3-0.3(La0.5Nd0.5)AlO3样品密度高、晶相均匀,其微波介电性能如下:εr=45.87,Q.f=41 612 GHz(4 GHz),τf=10×10–6/℃。     

Co_2O_3掺杂对0.965MgTiO_3-0.035SrTiO_3微波介质陶瓷性能的影响

采用传统电子陶瓷制备方法研究了Co2O3(1.5%～5.0%,质量分数)掺杂的0.965MgTiO3-0.035SrTiO3(MST0.035)微波介质陶瓷,分析了Co2O3含量对MST0.035陶瓷的烧结性能、晶相结构、显微形貌以及微波介电性能的影响。结果表明:Co2O3的掺杂促进了MST0.035陶瓷的烧结。随着Co2O3掺杂量的增加,陶瓷介电常数略有下降,谐振频率温度系数以及品质因数增加,同时中间相MgTi2O5逐渐减少直至完全消失。当Co2O3掺杂量为质量分数3.0%时,MST0.035陶瓷的烧结温度由1 380℃降低到1 290℃,其烧结所得的样品具有优良的微波介电性能:谐振频率温度系数τf=–2.53×10–6/℃,高的品质因数Q·f=19 006 GHz和介电常数εr=20.5。     

Activation Energy Spectra: Insights into Transport Limitations of Organic Semiconductors and Photovoltaic Cells

Some mechanisms of charge transport in organic semiconductors and organic photovoltaic (OPV) cells can be distinguished by their predicted change in activation energy for the current, E_a, versus applied field, F. E_a versus F is measured first in pure films of commercially available regioregular poly(3‐hexylthiophene) (P3HT) and in the same P3HT treated to reduce its charged defect density. The former shows a Poole–Frenkel (PF)‐like decrease in E_a at low F, which then plateaus at higher F. The low defect material does not exhibit PF behavior and E_a remains approximately constant. Upon addition of [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), however, both materials show a large increase in E_a and exhibit PF‐like behavior over the entire field range. These results are explained with a previously proposed model of transport that considers both the localized random disorder in the energy levels and the long‐range electrostatic fluctuations resulting from charged defects. Activation energy spectra in working OPV cells show that the current is injection‐limited over most of the voltage range but becomes transport‐limited, with a large peak in E_a, near the open circuit photovoltage. This causes a decrease in fill factor, which may be a general limitation in such solar cells.     

Understanding Boosted Selective CO2-to-CO Photoreduction with Pure Water Vapor over Hierarchical Biomass-Derived Carbon Matrix

Solar-driven CO₂ reduction reaction (CO₂RR) with water into carbon-neutral fuels is of great significance but remains challenging due to thermodynamic stability and kinetic inertness of CO₂. Biomass-derived nitrogen-doped carbon (N-C_b) have been considered as promising earth-abundant photocatalysts for CO₂RR, although their activities are not ideal and the reaction mechanism is still unclear. Herein, an efficient catalyst is developed for CO₂-to-CO conversion realized on diverse N-C_b materials with hierarchical pore structures. It is demonstrated that the CO₂-to-CO conversion preferentially takes place on positively charged carbon atoms next to pyridinic-N using two representatives treated pollens with the largest difference in pyridinic-N density and N content as model photocatalysts. Systematic experimental results indicate that surface local electric field originating from charge separation can be boosted by hierarchical pore structures, doped N, as well as pyridinic-N. Mechanistic studies reveal that positively charged carbon atoms next to pyridinic-N serve as active sites for CO₂RR, reduce the energy barrier on the formation of CO*, and facilitate the CO₂RR performance. All these benefits cooperatively contribute to treated chrysanthemum pollen catalyst exhibiting excellent CO formation rate of 203.2 µmol h⁻¹ g⁻¹ with 97.2% selectivity in pure water vapor. These results provide a new perspective into CO₂RR on N-C_b, which shall guide the design of nature-based photocatalysts for high-performance solar-fuel generation.