Emission Mechanism of High Al-content AlGaN Multiple Quantum Wells

紫外LED的发光功率和效率还远不能令人们满意,波长短于300 nm的深紫外LED的发光效率普遍较低。厘清高Al组分Al Ga N多量子阱结构的发光机制将有利于探索改善深紫外LED的发光效率的新途径、新方法。为此,本文通过金属有机气相外延技术外延生长了表面平整、界面清晰可辨且陡峭的高Al组分AlGa N多量子阱结构材料,并对其进行变温光致发光谱测试,结合数值计算,深入探讨了Al Ga N量子阱的发光机制。研究表明,量子阱中具有很强的局域化效应,其发光和局域激子的跳跃息息相关,而发光的猝灭则与局域激子的解局域以及位错引起的非辐射复合有关。The quantum efficiency of deep UV light emitting diodes( LED) drops dramatically with the increasing of Al content. Understanding the emission mechanism of high Al-content Al Ga N multiple quantum wells( MQW) is the one of the most important objects for improving the quantum efficiency of deep UV LED. In this work,high Al-content Al Ga N MQW structure with atomically flat hetero-interfaces was grown and characterized by photoluminescence( PL) measurements at different temperatures. The results indicate that there is a strong exciton-localization effect in the MQW structure and the emission is closely related to the hopping of the excitons. Due to the exciton delocalization and nonradiative recombination at defects,the PL intensity is strongly quenched at high temperatures.“973”国家重点基础研究发展计划(2012CB619300);; “863”国家高技术研究发展计划(2014AA032608);; 国家自然科学基金(U1405253;61227009;11204254;11404271);; 福建省自然科学基金(2015J01028)资助项

基于栖息地风险评价模型的海岸带滩涂湿地风险评价——以闽三角为例

海岸带湿地是生物多样性最丰富、生产力最高、最具价值的生态系统之一。然而近年来,随着城市化和工业化进程的加快,我国海岸带地区的土地利用正发生深刻变化,生态风险凸显。利用2000、2005、2010和2015年的Landsat TM/ETM+和Landsat 8 OLI遥感影像,融合行政区划图与地形图,并引入一个评价多元海洋、海岸带利用对栖息地造成风险的模型,即Integrated Valuation of Ecosystem Services and Trade-offs(In VEST)模型中的栖息地风险评价(Habitat Risk Assessment,HRA),模型评价闽三角海岸带滩涂湿地的生态风险。结果表明:(1)闽三角海岸带滩涂湿地风险以低风险为主;(2)泉州地区的风险面积最大(约4389.91 hm~2),漳州地区最小(约4630.73 hm~2);(3)修正面积影响的情况下,其他建设用地造成的暴露和影响较大,耕地造成的暴露和影响最小。不同区域滩涂湿地风险程度的可视化表达,可以揭示滩涂湿地高风险地区以及高风险的产生原因,便于管理者对滩涂湿地采取精准的保育措施。国家重点研发计划(2016YFC0502900);;福建省科学技术厅民生科技专项(引导性项目)(2017Y6002);;福建省自然科学基金资助项目(2015J01122

Development of high Al content structural Ⅲ nitrides and their applications in deep UV-LED

随着高gA组分Ⅲ族氮化物相关研究的日趋深入和生长技术的日益成熟,人们逐渐将研究重心转向具有更宽带隙的高Al组分Ⅲ族氮化物。该材料常温下带隙宽至6.2 EV,可覆盖短至210 nM的深紫外波长范围,具有耐高温、抗辐射、波长易调控等独特优点,因而是制备紫外发光器件的理想材料。目前,高Al组分Ⅲ族氮化物材料质量不高,所制备的深紫外lEd发光器件仍存在内量子效率、载流子注入效率和沿C轴方向正面出光效率较低的难题,因而制约了高效紫外发光器件的制备。本文着重介绍了近年来在高Al组分Ⅲ族氮化物生长动力学方面的研究进展,总结和梳理了量子结构设计、内电场调控以及晶体场调控等方面的相关研究,以期实现高质量深紫外lEd的制备。Along with the extensive investigations and growth technology maturation on high Ga content III-nitrides,researchers have moved their focus onto high Al content III-nitrides.Given a wider band gap up to 6.2 eV at room temperature,covering UV-light area as short as 210 nm,as well as other advantages of III-nitrides,high Al content III-nitrides are ideal materials for the fabrication of UV-light emitting devices.At present,there are certain challenges in the fabrication of UV-light emitting devices with high internal quantum efficiency,carrier injection efficiency and light-extraction efficiency due to the low quality materials.In this work,the progress on growth kinetics of high Al content III-nitrides in recent years has been reviewed comprehensively,and the corresponding researches in quantum structure design,internal electric field modification and crystalline field modification have been overviewed and analyzed.This review is expected to be informative for the fabrication of deep UV-LEDs.“973”规划项目(2012CB619301、2011CB25600); “863”计划项目(2011AA03A111); 国家自然科学基金项目(61227009、90921002); 中央高校基本科研业务费专项资金资助项目(2012121014、CXB2011029); 福建省自然科学基金计划项目(2012J01024

Growth of Thick Ge Epitaxial Layers with Low Dislocation Density on Silicon Substrate by UHV/CVD

采用超高真空化学气相淀积系统,以高纯Si2H6和GeH4作为生长气源,用低温缓冲层技术在Si(001)衬底上成功生长出厚的纯Ge外延层.对Si衬底上外延的纯Ge层用反射式高能电子衍射仪、原子力显微镜、X射线双晶衍射曲线和Ra-man谱进行了表征.结果表明在Si基上生长的约550nm厚的Ge外延层,表面粗糙度小于1nm,XRD双晶衍射曲线和Ra-man谱Ge-Ge模半高宽分别为530″和5.5cm-1,具有良好的结晶质量.位错腐蚀结果显示线位错密度小于5×105cm-2.可用于制备Si基长波长集成光电探测器和Si基高速电子器件.Thick Ge epitaxial layers are grown on Si(001) substrates with low temperature buffer layers with ultra-high vacuum chemical vapor deposition systems using Si2H6 and GeH4 as precursors.The deposition process of the Ge layer on Si is investigated in real time by reflection high-energy electron diffraction,and the quality of the Ge layer was evaluated by atomic force microscopy,double crystal X-ray diffraction(XRD),and Raman measurement.The root-mean-square surface roughness of the Ge epilayer with a thickness of 550nm is less than 1nm and the full-width-at-half maximum of the Ge peak of the XRD profile and the Ge-Ge mode of the Raman spectra are about 530″ and 5.5cm-1,respectively.These measurements indicate that the Ge epitaxial layer is of good quality.The etch pit density related to threading dislocations is less than 5×105cm-2.This is a promising material for Si-based long wavelength photodetectors and electronic devices国家自然科学基金(批准号:60676027,50672079,60336010);; 福建省重点科技项目(批准号:2006H0036);; 教育部回国留学人员启动基金资助项目~

UHV/CVD法生长硅基低位错密度厚锗外延层

采用超高真空化学气相淀积系统,以高纯Si_2H_6和GeH_4作为生长气源,用低温缓冲层技术在Si（001）衬底上成功生长出厚的纯Ge外延层.对Si衬底上外延的纯Ge层用反射式高能电子衍射仪、原子力显微镜、X射线双晶衍射曲线和Ra-man谱进行了表征.结果表明在Si基上生长的约550nm厚的Ge外延层,表面粗糙度小于1nm,XRD双晶衍射曲线和Ra-man谱Ge-Ge模半高宽分别为530″和5.5cm~(-1),具有良好的结晶质量.位错腐蚀结果显示线位错密度小于5×105cm~(-2).可用于制备Si基长波长集成光电探测器和Si基高速电子器件

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements