Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet(about 350 nm-360 nm) light-emitting diodes(LEDs) each with specifically designed irregular sawtooth electron blocking layer(EBL) by using the APSYS simulation program.The internal quantum efficiencies(IQEs),light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAl_xGa_(1-x)N irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.     

多尺度膨胀卷积神经网络资源三号卫星影像云识别

为提高影像云识别精度,提出一种多尺度膨胀卷积深层神经网络云识别方法。结合卫星影像特征,设计云识别卷积神经网络结构,该结构包含深层特征编码模块、局部多尺度膨胀感知模块以及云区预测解码模块。首先,编码模块中通过基础卷积层获取深度特征;其次,联合多尺度膨胀卷积和池化层共同感知,每层操作连接非线性函数,以提升网络模型的表达能力;最后,云区预测解码模块中融合对应编码模块的特征,再利用L1正则化上采样算法实现端对端的像素级云识别结果。选用典型云遮挡区域影像进行云识别实验,并与Otsu算法和FCN-8S算法进行对比。结果表明,本文所提算法的检测精度较高,Kappa系数显著提升。     

拟涡位移模型及气粒两相流动数值模拟

本文首先用离散涡方法对绕圆柱和半无限长平板的流动作了数值模拟。在讨论粒子和涡团耦合运动的基础上首次提出了粒子在流场中运动的拟涡位移模型，并对几个典型的气粒两相流动作了数值模拟。文章最后对流场中粒子运动的瞬时状态作了统计处理，得到了关于粒子在流场中分布的概率密度函数和粒子脉动速度的分布函数并用拟涡位移模型对壁面附近粒子的运动－沉积和反弹作了数值模拟。计算结果是令人满意的。     

多孔GaN/CuZnS异质结窄带近紫外光电探测器

窄带光电探测系统在荧光检测、人工视觉等领域具有广泛应用.为了实现对特殊波段的窄带光谱探测,传统上需要将宽带探测器和光学滤波片集成.但是,随着检测技术的发展,人们对探测系统的功耗、尺寸、成本等方面也提出了更高要求,结构复杂、成本高的传统窄带光电探测器应用受到限制.于是,本文展示了一种基于多孔GaN/CuZnS异质结的无滤波、窄带近紫外光电探测器.通过光电化学刻蚀和水浴生长方法,分别制备了具有低缺陷密度的多孔GaN薄膜和高空穴电导率的CuZnS薄膜,并构建了多孔GaN/CuZnS异质结近紫外光电探测器.得益于GaN的多孔结构和CuZnS的光学滤波作用,器件在–2 V偏压、370 nm紫外光照下,光暗电流比超过4个数量级;更重要的是,器件具有超窄带近紫外光响应(半峰宽<8 nm,峰值为370 nm).此外,该探测器的峰值响应度、外量子效率和比探测率分别达到了0.41 A/W, 138.6%和9.8×10¹² Jones.这些优异的器件性能显示了基于多孔GaN/CuZnS异质结的近紫外探测器在窄光谱紫外检测领域具有广阔的应用前景.     

Alleviating hysteresis and improving device stability of perovskite solar cells via alternate voltage sweeps

The anomalous hysteresis in a perovskite solar cell induced by an asymmetric field is confirmed by a capacitance–voltage measurement. By applying several cycles of alternating reverse and forward scans, this hysteresis phenomenon is obviously alleviated, resulting in a hysteresis-less state in the perovskite solar cell. Meanwhile, the open-circuit voltage and power conversion efficiency of the perovskite solar cell are enhanced by 55.74% and 61.30%, respectively, while the current density and fill factor keep almost invariable. The operation of alleviating hysteresis is essential for further research and is likely to bring in performance gains.