新型S型CdS-BiVO4异质结光电极的构筑及产氢性能研究

通过化学浴和连续离子层沉积法构筑了BiVO₄/CdS和CdS/BiVO₄两种S型异质结薄膜光电极. 利用扫描电子显微镜(SEM)、 X射线衍射(XRD)、 紫外-可见吸收光谱(UV-Vis)以及电化学阻抗谱(EIS)对其形貌、 结构和光电性能进行了表征, 测试了两种薄膜电极的光催化和光电催化产氢性能. 结果表明, CdS和BiVO₄之间形成S型异质结, BiVO₄/CdS表现出最佳的光催化产氢性能, 而CdS/BiVO₄表现出最佳的光电催化产氢性能. 借助表面光电压技术探究了两种薄膜电极中S型异质结内建电场的形成过程和载流子传输的机制.     

Photovoltage analysis of a heterojunction solar cell

According to the p-n junction model of Shockley,the relationship between the equilibrium carrier concentrations of n-type and p-type semiconductors on the edges of the depletion region of a p-n junction solar cell is analysed.The calculation results show that the photovoltage can exceed the built-in voltage for a special kind of heterojunction solar cell.When the photovoltage exceeds the built-in voltage under illumination,the dark current and the photocurrent are impeded by the peak of voltage barrier at the interface and the expression of the total I-V characteristic is given.     

Weak avalanche multiplication in SiGe heterojunction bipolar transistors on thin film silicon-on-insulator

In this paper, we propose an analytical avalanche multiplication model for the next generation of SiGe silicon-on-insulator (SOI) heterojunction bipolar transistors (HBTs) and consider their vertical and lateral impact ionizations for the first time. Supported by experimental data, the analytical model predicts that the avalanche multiplication governed by impact ionization shows kinks and the impact ionization effect is small compared with that of the bulk HBT, resulting in a larger base-collector breakdown voltage. The model presented in the paper is significant and has useful applications in the design and simulation of the next generation of SiGe SOI BiCMOS technology.     

Electronic Structure Effect of Polythiophene Derivatives and Nano N-Zn-Ag/TiO2 on Performance of Organic Thin Film Solar Cell

Nanocrystal N-Zn-Ag/TiO₂ powders were prepared with N-Zn/TiO₂ by photo deposition method. A series of pure polymers P3HT[poly(3-hexylthiophene)], P3OT[poly(3-octylthiophene)], P3DT[poly(3-decylthiophene)] and P3DDT[poly(3-dodecylthiophene)], was synthesized, which were used to synthesize p-n type semiconductor materials P3HT/N-Zn-Ag-TiO₂, P3OT/N-Zn-Ag-TiO₂, P3DT/N-Zn-Ag-TiO₂ and P3DDT/N-Zn-Ag-TiO₂ by in situ che-mical method. X-Ray diffraction(XRD) and infrared(IR) spectroscopy showed the structure of the polymers and complexes. Ultraviolet-visible(UV-Vis) spectra and cyclic voltammograms(CV) showed the optical and electronic performance of the polymers and complexes. Two new single and double organic thin film heterojunction solar cells were prepared with the above mentioned synthesized powders as raw materials. Current-voltage(I-V) measurements indicate that the conversion efficiency of the single organic thin film heterojunction solar cell is higher than that of the double organic thin film heterojunction solar cells. Single organic thin film heterojunction solar cells based on P3DT/N-Zn-Ag-TiO₂ can get a photoelectric conversion efficiency of 0.0408%. The performance of electronic transform between electron donor and acceptor on organic thin film solar cells was researched.     

Tuning electronic properties of the S_2/graphene heterojunction by strains from density functional theory

Based on the density functional calculations, the structural and electronic properties of the WS_2/graphene heterojunction under different strains are investigated. The calculated results show that unlike the free mono-layer WS_2, the monolayer WS_2 in the equilibrium WS_2/graphene heterojunctionis characterized by indirect band gap due to the weak van der Waals interaction. The height of the schottky barrier for the WS_2/graphene heterojunction is 0.13 eV, which is lower than the conventional metal/MoS_2 contact. Moreover, the band properties and height of schottky barrier for WS_2/graphene heterojunction can be tuned by strain. It is found that the height of the schottky barrier can be tuned to be near zero under an in-plane compressive strain, and the band gap of the WS_2 in the heterojunction is turned into a direct band gap from the indirect band gap with the increasing schottky barrier height under an in-plane tensile strain. Our calculation results may provide a potential guidance for designing and fabricating the WS_(2~-)based field effect transistors.     

Binary response Se/ZnO p‐n heterojunction UV photodetector with high on/off ratio and fast speed

A high‐performance UV photodetector (PD) based on a p‐Se/n‐ZnO hybrid structure with large area (more than 1×1 cm) is presented in this study. The device is theoretically equivalent to a parallel‐connection circuit for its special structure and shows multifunction at different voltage bias, which means the output signal can be tailored by an applied voltage. The Se/ZnO PD shows binary response (positive and negative current output under on/off periodical light illumination) under small reverse bias (–0.05 V and –0.1 V) which efficiently reduces the negative effect of noise signal in weak‐signal detection applications. At zero bias, with the aid of a p‐n heterojunction, a high on/off ratio of nearly 10⁴ is achieved by this device at zero set bias under 370 nm (∼0.85 mW cm⁻²) illumination and this on/off ratio can be achieved in 0.5 s. The device also shows a fast speed with rise time of 0.69 ms and decay time of 13.5 ms measured by a pulse laser, much faster than that of a pure ZnO film. The Se/ZnO PD in this research provides a new pathway to fabricate multifunctional high‐speed, high signal‐to‐noise ratio, high detectivity and high selectivity UV photodetectors.

     

nc-Si:H/c-Si硅异质结太阳电池中本征硅薄膜钝化层的优化

采用射频等离子体增强化学气相沉积(RF-PECVD)法在低温、低功率的条件下制备了一系列本征硅薄膜, 研究了硅烷浓度(C_S)对薄膜微结构、光电特性及表面钝化性能的影响. 将本征硅薄膜作为钝化层应用到氢化纳米晶硅/晶硅(nc-Si:H/c-Si)硅异质结(SHJ)太阳电池中, 研究了硅烷浓度和薄膜厚度对电池性能的影响. 实验发现: 随着硅烷浓度的降低, 本征硅薄膜的晶化率、氢含量、结构因子、光学带隙和光敏性等都在过渡区急剧变化; 本征硅薄膜的钝化性能由薄膜的氢含量及氢的成键方式决定. 靠近过渡区的薄膜具有较好的致密性和光敏性, 氢含量最高, 带隙态密度低, 且主要以SiH 形式成键, 对硅片表现出优异的钝化性能, 使电池的开路电压大幅提高. 但是, 当薄膜的厚度过小时, 会严重影响其钝化质量. 本实验中, 沉积本征硅薄膜的最优硅烷浓度为6% (摩尔分数), 且当薄膜厚度为~8 nm时, 所制备电池的性能最好. 实验最终获得了开路电压为672 mV, 短路电流密度为35.1 mA·cm^-2, 填充因子为0.73, 效率为17.3%的nc-Si:H/c-Si SHJ太阳电池     

掺杂非晶氧化硅薄膜中三元化合态与电子结构的第一性原理计算

基于密度泛函理论和分子动力学方法,研究了ITO-SiO_x(In,Sn)/n-Si异质结光伏器件中非晶SiO_x层的氧化态和电子结构.计算结果表明:具有钝化隧穿功能的超薄(2 nm)非晶SiO_x层,是由In,Sn,O,Si四种元素相互扩散形成的,其中In,Sn元素在SiO_x网格中以In-O-Si和Sn-O-Si成键态存在,形成了三元化合物.In和Sn的掺杂不仅在SiO_x的带隙中分别引入了E_v+4.60 eV和E_v+4.0 eV两个电子能级,还产生了与In离子相关的浅掺杂受主能级(E_v+0.3 eV).这些量子态一方面使SiO_x的性能得到改善,在n-Si表面形成与反型层相衔接的p-型宽禁带"准半导体",减少了载流子的复合,促进了内建电场的建立.另一方面有效地降低了异质结势垒高度,增强了ITO-SiO_x(In,Sn)/n-Si光伏器件中光生非平衡载流子的传输概率,促进了填充因子的提升(72%).     

A Low-Jitter Full-Rate 25-Gb/s CDR for 100-Gb/s Optical Interconnects in 0.13-μm SiGe BiCMOS

A low-jitter full-rate 25-Gb/s clock and data recovery (CDR) chip for 100-Gb/s optical interconnects is proposed. Fabricated in 0.13-μm SiGe BiCMOS technology, the chip is implemented in a third-order type-II bang-bang phase-locked loop (BBPLL) topology. To achieve optimal switching speed, all SiGe heterojunction bipolar transistors (HBTs) in high-speed blocks are biased at peak f_T current density. Transistors are sized by carefully balancing speed versus power consumption. Emitter-coupled logic (ECL) and current-mode logic (CML) are employed in logic components. Compared with conventional spiral inductors, the employment of RF transmission lines in resonators of the VCO reduces the area of the VCO and, thus, the whole chip, without sacrificing the performance. The core circuits occupy an area of 0.48 mm². The CDR recovers a clock with an rms jitter of 750 fs and a peak-to-peak jitter only of 3.46 ps.     

Study of a ternary blend system for bulk heterojunction thin film solar cells

In this research, we report a bulk heterojunction(BHJ) solar cell consisting of a ternary blend system. Poly(3-hexylthiophene) P3 HT is used as a donor and [6,6]-phenyl C61-butyric acid methylester(PCBM) plays the role of acceptor whereas vanadyl 2,9,16,23-tetraphenoxy-29 H, 31H-phthalocyanine(VOPc Ph O) is selected as an ambipolar transport material. The materials are selected and assembled in such a fashion that the generated charge carriers could efficiently be transported rightwards within the blend. The organic BHJ solar cells consist of ITO/PEDOT:PSS/ternary BHJ blend/Al structure. The power conversion efficiencies of the ITO/ PEDOT:PSS/P3HT:PCBM/Al and ITO/PEDOT:PSS/P3HT:PCBM:VOPcPhO/Al solar cells are found to be 2.3% and 3.4%, respectively.