Electro-optic coefficients of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice measured by polarization-maintaining fiber-optic Mach-Zehnder interferometer

Ten-period 5.5 nm Si0.75Ge0.25/10.3 nm Si/2.5 nm Si0.5Ge0.5 trilayer asymmetric superlattice was prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The stability of Mach-Zehnder interferometer was improved by utilizing polarization-maintaining fibers. According to the electro-optic responses of the superlattice with the light polarization along [110] and [-110], respectively, both electro-optic coefficients gamma(13) and gamma(63) of such asymmetric superlattice were measured. gamma(13) and gamma(63) are 2.4x10(-11) and 1.3x10(-11) cm/V, respectively, with the incident light wavelength at 1.55 mu m. (c) 2006 American Institute of Physics.

1.55-mu m resonant cavity enhanced photodiode based on MBE grown Ge quantum dots

Self-assembly Ge quantum dots (QD) on Si and Si/Ge mutli-quantum-wells (MQW) are grown by MBE. The island size and island density was investigated by atomics force microscopy. Ten-layer and twenty-layer MQW were selected for photodiode device fabrication. In photoluminescence (PL), a broad peak around 1.55-mu m wavelength was observed with higher peak intensity for the 10-layer MQW which had less defects than the 20-layer sample. Resonant cavity enhanced (RCE) photodiodes were fabricated by bonding on a SOI wafer. Selected responsivity at 1.55 mu m was successfully demonstrated. (c) 2005 Elsevier B.V. All rights reserved.

Study on in-plane optical anisotropy of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice by reflectance difference spectroscopy - art. no. 071908

Si0.75Ge0.25/Si/Si0.5Ge0.5 trilayer asymmetric superlattices were prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The nonlinear optical response caused by inherent asymmetric interfaces in this structure predicted by theories was verified by in-plane optical anisotropy in (001) plane measured via reflectance difference spectroscopy. The results show Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice is optically biaxial and the two optical eigen axes in (001) plane are along the directions [110] and [-110], respectively. Reflectance difference response between the above two eigen axes can be influenced by the width of the trilayers and reaches as large as similar to 10(-4)-10(-3) in 15-period 2.7 nm-Si0.75Ge0.25/8 nm-Si/1.3 nm-Si0.5Ge0.5 superlattice when the normal incident light wavelength is in the range of 500-1100 nm, which is quite remarkable because the optical anisotropy does not exist in bulk Si.

Impact of wide bandgap p-type nc-Si on the performance of a-Si solar cells

This paper reports the impact of a wide bandgap p-type hydrogenated nanocrystalline silicon (nc-Si:H) on the performances of hydrogenated amorphous silicon (a-Si:H) based solar cells. The player consists of nanometer-sized Si crystallites and has a wide effective bandgap determined mainly by the quantum size-confinement effect (QSE). By incorporation of this p-layer into the devices we have obtained high performances of a-Si:H top solar cells with V-infinity=1.045 V and FF=70.3 %, and much improved mid and bottom a-SiGe:H cells, deposited on stainless steel (SS) substrate. The effects of the band-edge mismatch at the p/i-interface on the I-V characteristics of the solar cells arc discussed on the bases of the density-functional approach and the AMPS model.

Si-based resonant-cavity-enhanced photodetector

We report one top-illumination and one bottom-illumination SiGe/Si multiple quantum-well (MQW) resonant-cavity-enhanced (RCE) photodetector fabricated on a separation-by-implanted-oxygen (SIMOX) wafer operating near 1300 nm. The buried oxygen layer in SIMOX is used as a mirror to form a vertical cavity with the silicon dioxide/silicon Bragg reflector deposited on the top surface. A peak responsivity with a reverse bias of 5 V is measured 10.2 mA/W at 1285 nm, a full width at half maximum of 25 nm for the top-illumination RCE photodetector, 19 mA/W at 1305 nm, and a full width at half maximum of 14 nm for the bottom-illumination one. The external quantum efficiency of the bottom-illumination RCE photodetector is up to 2.9% at 1305 nm, with a reverse bias of 25V. The responsivity of the bottom-illumination RCE photodetector is improved by two-fold compared with that of the top-illumination one. (C) 2001 Society of Photo-Optical Instrumentation Engineers.

A surface kinetics model for the growth of Si1-xGex by UHV/CVD using SiH4/CeH4

The surface reaction mechanism of Si1-xGex/Si growth using SiH4 and GeH4 in UHV/CVD system was studied. The saturated adsorption and desorption of SiH4 from Si(1 0 0) surface was investigated with the help of TPD and RHEED, and it was found that all the 4 hydrogen atoms of one SiH4 molecule were adsorbed to the Si surface, which meant that the dissociated adsorption ratio was proportional to 4 power of surface vacancies. The analysis of the reaction of GeH4 was also done. A new surface reaction kinetic model on Si1-xGex/Si epitaxial growth under UHV conditions by SiH4/GeH4 was proposed based on these studies. The predictions of the model were verified by the experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.

Relaxed GexSi1-x layer formation with reduced dislocation density grown by ultrahigh vacuum chemical vapor deposition

A new alternative method to grow the relaxed Ge0.24Si0.76 layer with a reduced dislocation density by ultrahigh vacuum chemical vapor deposition is reported in this paper. A 1000-Angstrom Ge0.24Si0.76 layer was first grown on a Si(100) substrate. Then a 500-Angstrom Si layer and a subsequent 5000-Angstrom Ge0.24Si0.76 overlayer followed. All these three layers were grown at 600 degrees C. After being removed from the growth system to air, the sample was first annealed at 850 degrees C for 30 min, and then was investigated by cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy. It is shown that the 5000-Angstrom Ge0.24Si0.76 thick over layer is perfect, and most of the threading dislocations are located in the embedded thin Si layer and the lower 1000-Angstrom Ge0.24Si0.76 layer. The relaxation ratio of the over layer is deduced to be 0.8 from Raman spectroscopy.

A study of Si1-xGex/Si quantum-well intermixing by photocurrent spectroscopy

Photocurrent spectroscopy has been used to study quantum-well intermixing in this paper. The cut-off wavelength of the photodiodes based on the implanted and annealed materials is significantly reduced, compared with that measured in annealed-only photodetectors. The bandgap of SiGe quantum well in implanted and annealed samples is blue-shifted by up to 97 meV, relative to that in annealed-only samples. (C) 2000 Elsevier Science S.A. All rights reserved.

Effect of Si overgrowth on the structural and luminescence properties of Ge islands on Si(100)

The effect of Si overgrowth on the structural and luminescence properties of strained Ge layer grown on Si(1 0 0) is studied. Capping Si leads to the dissolution of Ge island apex and reduced island height. The structural changes in island shape, especially in chemical composition during Si overgrowth have a large effect on the PL properties. The integrated PL intensity of Ge layer increases and there are large blue shifts in peak energies after capping Si. The PL spectra from buried Ge layer are consistent with type-II band alignment in SiGe/Si. We show that the PL properties from buried Ge layer may be tailored by modifying the cap layer growth conditions as well as post-growth annealing. (C) 1999 Elsevier Science B.V. All rights reserved.

Si-based optoelectronic devices and their attractive applications

The semiconductor photonics and optoelectronics which have a great significance in the development of advanced high technology of information systems will be discussed in this paper. The emphasis will be put on the recent research carried out in our laboratory in enhanced luminescence from low dimensional materials such as SiGe/Si and Er-doped Si-rich SiO2/Si and Er-doped SixNy/Si. A ring shape waveguide structure, used to promote the effective absorption coefficient in PIN photodetector for 1.3 mu m wavelength and a resonant cavity enhanced structure, used to improve the quantum efficiency and response in heterostructure photo-transistor (HPT), are also proposed in this paper.

High phosphorous doping and morphological evolution during Si growth by gas source molecular beam epitaxy (GSMBE)

Uniform and high phosphorous doping has been demonstrated during Si growth by GSMBE using disilane and phosphine. The p-n diodes, which consist of a n-Si layer and a p-SiGe layer grown on Si substrate, show a normal I-V characteristic. A roughening transition during P-doped Si growth is found. Ex situ SEM results show that thinner film is specular. When the film becomes thicker, there are small pits of different sizes randomly distributed on the flat surface. The average pit size increases, the pit density decreases, and the size distribution is narrower for even thicker film. No extended defects are found at the substrate interface or in the epilayer. Possible causes for the morphological evolution are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Boron diffusion in Ge+ premorphized and BF2+ implanted Si(001)

The annealing behavior of Si implanted with Ge and then BF2 has been characterized by double crystal X-ray diffraction (DCXRD) and secondary ion mass spectroscopy (SIMS). The results show that annealing at 600 degrees C for 60 minutes can only remove a little damage induced by implantation and nearly no redistribution of Ge and B atoms has occurred during the annealing. The initial crystallinity of Si is fully recovered after annealing at 950 degrees C for 60 minutes and accompanied by Ge diffusion. Very shallow boron junction depth has been formed. When annealing temperature rises to 1050 degrees C, B diffusion enhances, which leads to a deep diffusion and good distribution of B atoms into the Si substrate. The X-ray diffraction (004) rocking curves from the samples annealed at 1050 degrees C for 60 minutes display two SiGe peaks, which may be related to the B concentration profiles.

Characterization of strain relaxation in As ion implanted Si1-xGex epilayers grown by gas source molecular beam epitaxy

Strain relaxation in the As ion implanted Si0.57Ge0.43 epilayers was studied by double-crystal x-ray diffractometry and transmission electron microscopy, and was compared to that in the nonimplanted Si0.57Ge0.43 epilayers. Experimental results show that after rapid thermal annealing (RTA) the x-ray linewidth of the As+-implanted Si0.57Ge0.43 epilayers is narrower than that of the nonimplanted epilayers, and than that of the partially relaxed as-grown samples, which is due primarily to low density of misfit dislocations in the As+-implanted SiGe epilayers. RTA at higher than 950 degrees C results in the formation of misfit dislocations for the nonimplanted structures, and of combinations of dislocations and precipitates (tentatively identified as GeAs) for the As+-implanted epilayers. The results mean that the strain relaxation mechanism of the As+-implanted Si1-xGex epilayers may be different from that of the nonimplanted Si1-xGex epilayers. (C) 1998 American Institute of Physics.

中国材料工程大典—信息功能材料工程

本书是《中国材料工程大典》中的卷目之一。 信息功能材料是信息科学技术和信息产业发展的基础和先导。21世纪将是以信息产业为核心的知识经济时代，对信息技术和信息资源的竞争将更加激烈。我国电子信息行业2004年完成产品销售收入达26500亿元，多年来已居外贸出口首位，并继续以高出工业发展速度10％的速度发展，已成为世界信息产业大国。加快由信息产业大国向信息产业强国迈进的步伐，是我们广大从事信息技术，特别是信息功能材料工作者义不容辞的责任。希望《中国材料工程大典》中《信息功能材料工程》卷的出版，将有力推动我国信息技术和信息产业的健康发展。 《信息功能材料工程》分上、中、下卷，共设20篇，约600万字。它涉及到信息的获取、传输、存储、显示和处理等主要技术用的材料与器件，是目前我国该领域比较完整的专业工具书。参加这部书编写的有中科院、高校和部分企业的专家教授近200名。参加编写的主要单位有中科院半导体研究所、中科院物理研究所、中科院微电子研究所、中科院上海精密光学机械研究所、中科院上海红外技术物理研究所、中科院长春应用化学研究所、中科院合肥固体物理所、南京大学、清华大学、西安理工大学、北京有色金属研究总院、武汉邮电科学研究院等。历时近3年完稿。由王占国、陈立泉、屠海令任主编并统稿。 本卷各篇不仅全面系统地反映了国外信息功能材料研究领域的现状、最新进展和发展趋势，而且也特别注重我国在该领域的研发和产业化方面取得的成果，力图使其具有实用性、先进性和权威性。本书适合于从事信息功能材料的科研工作者和工程技术人员查阅使用，也可供有关师生参考。

A direct-conversion mixer with a DC-offset cancellation for WLAN

This paper presents a 5GHz double-balanced mixer with DC-offset cancellation circuit for direct-conversion receiver compliant with IEEE 802.11a wireless LAN standard. The analog feedback loop is used, to eliminate the DC-offset at the output of the double-balanced mixer. The test results show that the mixer with DC-offset cancellation circuit has voltage conversion gain of 9.5dB at 5.15GHz, noise figure of 13.5dB, IIP3 of 7.6 dBm, 1.73mV DC-offset voltage and 67mW power with 3.3-V power supply. The DC-offset cancellation circuit has less than 0.1mm(2) additional area and 0.3mW added power dissipation. The direct conversion WLAN receiver has been implemented in a 0.35 mu m SiGe BiCMOS technology.