The Si/SiGe quantum cascade laser

Si/SiGe量子级联激光器是一种新型的带内跃迁的红外光源,突破了Si基材料间接带隙特性对光跃迁的限制.Si/SiGe量子级联激光器的开发将为实现太赫兹有源器件的硅基集成产生深远影响.文章介绍了Si/SiGe量子级联激光器的工作原理,以及这类激光器在能带设计、材料生长和波导制作方面的最新进展.The Si/SiGe quantum cascade laser is a new coherent IR source based on intersubband transitions, which overcomes the limitations imposed by the indirect gap. This laser will have a great impact on the development of terahertz devices and indicates a possible way to integrate active terahertz devices into silicon-based technology. In this paper we will describe the principle and latest progress in the active layer design, materials growth, and waveguide fabrication of this Si-based laser.国家自然科学基金(批准号:60576001)资助项

Growth of high quality Ge epitaxial films on Si substrate by low temperature buffer technique

采用低温缓冲层技术,在SI衬底上生长了质量优良的gE薄膜。利用原子力显微镜(AfM)、双晶X射线衍射(Xrd)和拉曼散射等研究了薄膜的晶体质量。结果表明,由于无法抑制三维岛状生长,低温gE缓冲层的表面是起伏的。然而,gE与SI间的压应变几乎完全弛豫。当缓冲层足够厚时,后续高温gE外延层的生长能够使粗糙的表面变得平整。在90 nM低温gE缓冲层上生长的210 nM高温gE外延层,表面粗糙度仅为1.2 nM,位错密度小于5x105CM-2,Xrd的峰形对称,峰值半高宽为460 ArC SEC。High-quality and thick Ge epitaxial films are grown on Si substrates utilizing the low-temperature(LT) buffer technique by ultrahigh vacuum chemical vapor deposition(UHV-CVD) and are characterized by atomic force microscope,X-ray diffraction,and Raman spectroscopy.The results show that the LT Ge buffer is rough due to the three-dimensional islands formations,but the misfit stress is nearly fully relaxed.Fortunately,the rough LT Ge surface is effectively smoothed by subsequent growth at elevated temperature when the LT Ge buffer is thick enough and the compressive strain is largely relaxed.Finally,the 210 nm Ge epitaxial film with smooth surface(root-mean-square roughness of 1.2 nm),low threading dislocation density(5×105 cm-2),and sharp and symmetric X-ray diffraction peak(full width at half maximum of ～460 arc sec) is achieved on LT Ge buffer with thickness of 90 nm.国家重点基础发展研究计划资助项目(2007CB613404

Research and fabrication of silicon based metal-semiconductor-metal photodetector with U-shape trench interdigitated electrodes

为了提高硅MSM结构光电探测器的光电响应度,制备了U型凹槽电极结构的探测器。5 V偏压下,对650 nm波长入射光的绝对光电响应度测试表明,凹槽电极结构的探测器最大光电响应度值为0.486 A/W,比同样尺寸的平版结构光电探测器提高了约6倍。文中也对比了具有抗反射膜和不具有抗反射膜的器件相对响应光谱的差别,并且比较分析了叉指间隙分别为5μm和10μm器件光电响应的不同。The responsivity of silicon based metal-semiconductor-metal(MSM) photodetector(Si-MSM-PD) was improved by placing the planar interdigitated electrodes with U-shape trench interdigitated electrodes.The performance test indicates that the responsivity of Si-MSM-PD with U-shape trench interdigitated electrodes is 0.486 A/W for 650 nm laser at 5 V applied voltage.This responsivity is about 6 times larger than that of Si-MSM-PD with planar interdigitated electrodes whose responsivity is just 0.084 A/W.Besides,the performance of Si-MSM-PDs with different intergitated space of 5 μm and 10 μm was compared.国家自然科学基金资助项目(60576001,60336010,60676027);; 福建省自然科学基金资助项目(A0410008

Growth of High-reflectivity AlN/GaN Distributed Bragg Reflectors in Blue Region

采用金属有机物化学气相沉积方法制备了蓝光波段高反射率Aln/gAn分布布拉格(dbr)反射镜。利用金相显微镜、扫描电子显微镜、原子力显微镜以及分光光度计等测量手段对样品的物理特性进行了分析表征。结果显示样品的表面有少量圆形台面结构和裂纹出现,但在其他区域,样品具有较为平整的表面。该样品在462.5 nM附近获得最大反射率99.4%,表面均方根粗糙度小至2.5 nM。分析表明,所得dbr达到了制备gAn基垂直腔面发射激光器的要求。One high-reflectivity AlN/GaN distributed Bragg reflector(DBR) in blue region was grown with the method of metalorganic chemical vapor deposition(MOCVD).perties of the sample were analyzed by using,scanning electron microscope(SEM),atomic force microscopy(AFM) and spectrophotometer.Except for the circular mesa structure and a few cracks observed on the surface,the sample showed a rather smooth surface.A peak reflectivity of 99.4% was observed around 462.5 nm and the surface roughness was as small as 2.5nm.The properties of the DBR meet the requirements of GaN-based vertical cavity surface emitting lasers(VCSEL).国家“863”计划资助项目(2006AA03Z409

Luminescence of Strain Compensated Si/Si_(0.62)Ge_(0.38) Quantum Well Grown on Si_(0.75)Ge_(0.25) Virtual Substrate

由于SI/SIgE异质结构的带阶差主要发生在价带,为实现高效率的发光,本文从理论上设计了在硅基SI1-XgEX虚衬底上外延应变补偿的SI/S1-ygEy(y>X)量子阱的能带结构,将量子阱对电子的限制势垒提高到100MEV以上。在实验上,采用300℃生长的gE量子点插入层,制备出薄的SIgE驰豫缓冲层(虚衬底),表面gE组份达到0.25,表面粗糙度小于2nM,驰豫度接近100%。在我们制备的SIgE缓冲层上外延了应变补偿SIgE/SI多量子阱结构,并初步研究了其发光特性。In this paper,band structures of strain compensated Si/S_(1-y)Ge_y(y>x) quantum well grown on Si_(1-x)Ge_x virtual substrate was design to enlarge the conduction band offset up to 100meV for improving luminescence.The fully strain-relaxed Si_(0.75)Ge_(0.25) virtual substrate was prepared by inserting a low-temperature Ge islands layer in ultra-high vacuum chemical deposition.The root-mean-square surface roughness of the virtual substrate is less than 2nm.The luminescence of the strain compensated Si/SiGe quantum well on the virtual substrate was investigated.国家重点基础研究发展计划资助项目2007CB613400;国家自然科学基金资助项目(60676027;50672079

MOCVD growth of high-reflectivity AlN/GaN distributed Bragg reflectors

利用金属有机物化学气相沉积(MOCVD)方法在蓝宝石c面衬底上制备出高反射率AlN/GaN分布布拉格反射镜(DBR)。利用分光光度计测量,在418 nm附近最大反射率达到99%。样品表面显微照片显示,有圆弧形缺陷和少量裂纹出现;在缺陷和裂纹以外的区域,DBR具有较为平坦的表面,其粗糙度在10μm×10μm面积上为3.3 nm左右。样品的截面扫描电镜(SEM)照片显示,DBR具有良好的周期性。对反射率和表面分析的结果表明,该样品达到了制备GaN基垂直腔面发射激光器(VCSEL)的要求。A high reflectivity AlN/GaN distributed Bragg reflector(DBR) is grown on c-plane sapphire substrate by metalorganic chemical vapor deposition(MOCVD).A peak reflectivity of 99% is observed around 418 nm by spectrophotometer.Compass-shape defects and a few cracks are observed on the surface.The surface root mean square(RMS) of roughness in the flat area is around 3.3 nm over a 10 μm×10 μm area.The cross-sectional scanning electron microscope(SEM) image reveals the good periodicity of DBR.Considering the peak reflectivity and surface morphology,the DBR can be used to fabricate GaN-based vertical cavity surface emitting laser(VCSEL).国家高技术研究“863”计划资助项目(2006AA03Z409