Photovoltaic performance and stability of CdTe/polymeric hybrid solar cells using a C60 buffer layer

The influence of C₆₀ as a buffer layer on photovoltaic performance and stability of bulk hetero-junction solar cells using a photoactive layer of CdTe nanocrystals and poly(p-phenylenevinylene) derivative has been investigated. The incident photon-to-current conversion efficiency of the sealed-cells with a C₆₀ buffer layer was about 70% of that of solar cells using a buffer layer of LiF. The introduction of C₆₀ buffer layer gave an improvement in the stability for a light-harvesting test. In a long-term thermal stability test, there was no difference between the solar cells using C₆₀ and LiF. An impedance analysis suggested that the degradation of the performance in the stability tests was associated with a decrease in the conductance of the cells.     

一种低噪声GaAs HBT VCO的设计与实现

为了降低双极型工艺中二极管对相位噪声的影响,实现了一种工作在K波段的全集成差分压控振荡器．该振荡器基于砷化镓异质结双极晶体管工艺来实现,电路采用改进的π形反馈网络来提高振荡回路的品质因数,降低了压控振荡器的相位噪声,并补偿了电路本身存在的180°相位偏移．芯片的频率变化范围为23.123GHz到23.851GHz,最大输出功率为-1.68dBm; 整个电路由-6V的电源供电,直流功耗为72mW,控制电压为-3V时相位噪声为-103.12dBc／Hz@1MHz,芯片面积为0.49mm²．文中采用的电路结构能够降低双极型工艺中二极管对压控振荡器相位噪声的影响,在不牺牲压控振荡器调谐宽度的情况下可实现低的相位噪声．     

Effects of Buffer Layer on Hetero-Epi-Growth of SiCGe on 6H-SiC

Growth of SiCGe ternary alloy on 6H-SiC in a conventional hot-wall CVD system was initially studied. SiH4, GeH4 and C3H8 were employed as silicon, germanium and carbon source, respectively, while H2 was employed as the carrier gas. To reduce the heavy lattice mismatch between the film and the substrate, a 3C-SiC buffer layer was inserted between them in a CVD process. Optimizing the growth conditions was discussed. The samples were measured by means of SEM, SAXRD (Small Angle X-Ray Diffraction). It is shown that use of the 3C-SiC buffer layer is an effective way to improve the quality of the ternary alloy.     

Synthesis and photovoltaic properties of new small molecules with rhodanine derivative as the end-capped blocks

Two new acceptor–donor–acceptor (A–D–A) type small molecules DCAO3TIDT and DCNR3TIDT, with 4,4,9,9-tetrakis(4-(dodecyloxy)phenyl)-4,9-dihydro-s-indaceno-[1,2-b:5,6-b′]dithiophene (IDT) as the core group and 2-ethylhexyl cyanoacetate (CAO) and 2-(1,1-dicyanomethylene)-3-octyl rhodanine (CNR) as different end-capped blocks, have been designed and synthesized. Both of them have been employed as donor for solution-processed bulk hetero-junction (BHJ) organic solar cells (OSCs). The two compounds showed deep highest occupied molecular orbital (HOMO) energy levels (∼−5.30 eV) and strong absorption. The DCAO3TIDT and DCNR3TIDT with PC₇₁BM as acceptor based BHJ solar cell devices showed short circuit current density (J_sc) of 6.93 mA/cm² and 8.59 mA/cm², power conversion efficiency (PCE) of 3.34% and 4.27%, respectively, and with almost same open-circuit voltage (∼0.93 V), under the illumination of AM 1.5 G, 100 mW/cm². The high J_sc for DCNR3TIDT could result from its wider and red-shifted absorption than that of DCAO3TIDT, which was probably induced by the end-capped block rhodanine derivative. The results demonstrate that the end group would be taken into full account when designing new solution-processed small molecules, which is an important factor to determine their photovoltaic properties.     

On the buckling behavior of perfect and atomically defective hetero-junction carbon nanotubes

Bent and straight hetero-junction carbon nanotubes and their constructive homogeneous tubes were modeled based on the finite element method in their perfect and atomically defective forms with silicon impurities and carbon vacancies, and their buckling behavior was investigated. The results showed that the buckling strength of hetero-junction carbon nanotubes, which depends on the size of their kink and their constructive tubes' diameters, lies in the range of their constructive tubes' buckling strength. Armchair-armchair and zigzag-zigzag models also demonstrated higher buckling strength than the other hetero-junction models. Finally, the atomic defects were seen to considerably decrease the buckling strength of these nanomaterials.     

极化调控AlGaN基日盲紫外雪崩光电二极管性能优化

通过数值模拟研究了各层参数对极化调控的背入射异质结分离吸收倍增层型AlGaN基雪崩光电二极管(APDs)性能的影响,并详细分析相关物理机制。计算结果表明:参数的优化有利于降低APDs的雪崩击穿电压,提高倍增因子。特别是对于P-GaN层AlGaN雪崩光电二极管,倍增因子增加可超过300%,这是由于该雪崩光电二极管的GaN/Al0.4Ga0.6N异质界面的强极化电荷调节了倍增层、中间插入层、吸收层的电场分布,增加了载流子的注入和倍增效率,同时还由于参数优化减小了倍增时的暗电流。     

有机半导体的异质结(Hetero-junction)问题

有机异质结在有机电子器件中起到十分重要的作用,它不仅对有机器件中载流子的运动起到控制和调节的作用,而且对器件的基本功能特征,诸如光-电转换,电-光转换器件中某些要害步骤(如电子转移,能量转移等)起到重要的作用.本文扼要地从层间能量关系对有关有机异质结进行分类和讨论,并对异质结的界面能量关系中存在的问题及其进展作了介绍.显然,这将对有关器件设计的思路有所帮助.     

两种新结构SiGe/Si功率二极管特性模拟

提出了在 n- 区中采用掺杂浓度三层渐变式结构 Si Ge/Si功率二极管及台面结构的 Si Ge/Si功率二极管。由 Medici模拟所得的特性表明 ,在采用 n- 区渐变掺杂结构的 p+ ( Si Ge) -n- -n+ 功率二极管中 ,在正向特性基本不发生变化的前提下 ,与 n-区固定掺杂结构相比反向恢复过程加快 ,二极管下降时间 t A 缩短近 1 /2 ;在采用台面结构的 p+ ( Si Gi) -n- -n+功率二极管中 ,反向恢复特性也有明显改进 ,电流反向恢复时间缩短近 1 /3 ,而电压反向恢复时间缩短近 1 /2。     

金刚石/氧化锌透明异质结的研制

利用化学气相沉积和磁控溅射方法制备了透明金刚石薄膜／氧化锌异质结。首先,在金刚石单晶表面外延生长1层透明p型半导体金刚石薄膜,然后在金刚石薄膜上利用反应磁控溅射方法制备出n型透明氧化锌半导体薄膜;进而利用溅射、光刻等方法制备出欧姆接触电极,获得了金刚石／氧化锌透明异质pn结。该结呈现典型的二极管伏安特性曲线,开启电压为1．0V。在500～700nm波长范围内,该结的透过率达到20％。     

A 75 GHz regenerative dynamic frequency divider with active transformer using InGaAs/InP HBT technology

This letter presents a high speed 2:1 regenerative dynamic frequency divider with an active transformer fabricated in 0.7 μm InP DHBT technology with f_T of 165 GHz and f_max of 230 GHz. The circuit includes a two-stage active transformer, input buffer, divider core and output buffer. The core part of the frequency divider is composed of a double-balanced active mixer (widely known as the Gilbert cell) and a regenerative feedback loop. The active transformer with two stages can contribute to positive gain and greatly improve phase difference. Instead of the passive transformer, the active one occupies a much smaller chip area. The area of the chip is only 469×414 μm² and it entirely consumes a total DC power of only 94.6 mW from a single -4.8 V DC supply. The measured results present that the divider achieves an operating frequency bandwidth from 75 to 80 GHz, and performs a -23 dBm maximum output power at 37.5 GHz with a 0 dBm input signal of 75 GHz.