GaAs基短周期InAs/GaSb超晶格红外探测器研究

采用分子束外延(MBE)方法,在(001)GaAs衬底上生长了短周期Ⅱ型超晶格(SLs):InAs/GaSb (2ML/8ML)和InAs/GaSb (8ML/8ML).从X射线衍射(HRXRD)中计算出超晶格周期分别为31.2和57.3.室温红外透射光谱表明两种超晶格结构在短波2.1μm和中波5μm处有明显吸收.通过腐蚀、光刻和欧姆接触,制备了短波和中波的单元光导探测器.在室温和低温下进行光谱响应测试和黑体测试,77K下,50%截止波长分别为2.1μm和5.0μm,黑体探测率D·bb均超过2×108cmHz1/2/W.室温下短波探测器D·bb超过108cmHz1/2/W.     

SiGe／Si异质结器件

本文综述了国际上ＳｉＧｅ／Ｓｉ异质结器件的发展状况，分析了该器件的结构要理，特点，优越性及制造技术，阐述了该器件的广阔应用和对微电子将产的重大影响。     

Si／SiGe／Si HBT的优化设计

给出了常温和低温Ｓｉ／ＳｉＧｅ／ＳｉＨＢＴ的设计原则，并进行了讨论。指出了低温和室温ＨＢＴ设计上的差异。这些原则可用于设计特定要求的Ｓｉ／ＳｉＧｅ／ＳｉＨＢＴ。     

射频Si/SiGe/Si HBT的研究

在Si／SiGe／SiHBT与Si工艺兼容的研究基础上，对射频Si／SiGe／SiHBT的射频特性和制备工艺进行了研究，分析了与器件结构有关的关键参数寄生电容和寄生电阻与Si／SiGe/Si HBT的特征频率fT和最高振荡频率fmax的关系，成功地制备了fT为2．5CHz、fmax为2．3GHz的射频Si／SiGe／SiHBT，为具有更好的射频性能的Si／SiGe／Si HBT的研究建立了基础。     

采用低温Si技术的Si/SiGe异质结P-MOSFET

针对S i/S iG e p-M O SFET的虚拟S iG e衬底厚度较大(大于1μm)的问题,采用低温S i技术在S i缓冲层和虚拟S iG e衬底之间M BE生长低温-S i层。S iG e层应力通过低温-S i层释放,达到应变弛豫。XRD和AFM测试表明,S i0.8G e0.2层厚度可减薄至300 nm,其弛豫度大于85%,表面平均粗糙度仅为1.02 nm。试制出应变S i/S iG e p-M O SFET器件,最大空穴迁移率达到112 cm2/V s,其性能略优于目前多采用1μm厚虚拟S iG e衬底的器件。     

功率SiGe/Si HBT的温度特性

测量了Si/SiGe HBT在23~260℃温度范围内的Gummel图、理想因子n、不同基极电流下的发射结电压VBE、电流增益β、共发射极输出特性,以及Early电压VA的变化情况。结果表明,随电流和温度的增加,β减少,VBE随温度的变化率dVBE/dT小于同质结Si BJT。在高集电极-发射极电压和大电流下,在输出特性曲线上观察到了负微分电阻(NDR)特性。结果还显示,电流增益-Early电压积与温度的倒数(1/T)呈线性关系,这对模拟电路应用是很重要和有用的。     

Theoretical small-signal performance of Si/SiGe/Si HBT

Application of the Monte Carlo technique to analyze electron and hole transport in bulk Si_0.8Ge_0.2 and strained Si _0.8Ge_0.2/Si is discussed. The computed minority- and majority-carrier transport properties were used in a comprehensive small-signal model to evaluate the high-frequency performance of a state-of-the-art n-p-n heterostructure bipolar transistors (HBT) fabricated with SiGe as the base material. The valence band discontinuity of a SiGe-base HBT reverses the degradation in emitter injection efficiency caused by bandgap narrowing in the base, and permits a higher ratio of base doping to emitter doping than would be practical for a bipolar transistor. Any degradative effect of increased base doping on electron and hole mobilities is offset by improved transport in the strained SiGe base, resulting in a marked decrease in the base resistance and base transit time. Compared to the Si BJT, the use of Si_0.8Ge_0.2 for the base region of an HBT leads to significant improvements in low-frequency common emitter current gain, low-frequency unilateral power gain, and maximum oscillation frequency     

Spontaneous lateral composition modulation in AlAs/InAs short period superlattices via the growth front

The spontaneous formation of lateral composition modulation in AlAs/lnAs short period superlattices on InP (001) substrates has been investigated. Transmission electron microscopy and x-ray diffraction reciprocal space mapping show that the lateral modulation is very regular, with a periodicity along the [110] direction on the order of 180Å. A surprising: result is that this material system also exhibits a lateral modulation along the [1–10] direction, with a periodicity of 330Å. Reflection high energy electron diffraction performed during the deposition revealed that the reconstruction changed from (2 × 1) during the InAs deposition cycle to (1 × 2) during the AlAs cycle, which may be related to the presence of the modulation in both <110> directions. High magnification transmission electron micrographs show that the surface is undulated and that these undulations correlate spatially with composition modulation. Detailed analysis of the images shows that the contrast observed is indeed due to composition modulation. Photoluminescence from the modulated layer is strongly polarized and red-shifted by 220 meV.     

GeSi/Si Mach-Zehnder干涉型调制器的研制

基于ＧｅＳｉ合金的等离子体色散效应,研制了一种Ｍａｃｈ－Ｚｅｈｎｄｅｒ干涉型调制器,通过对其损耗和调制特征的测试得到：调制器对１．３μｍ光的插入损耗为６．５ｄＢ,最大调制深度达８５％,相应的π相移调制民压为０．９Ｖ,关断电流和调制区的注入电流密度分别为４０ｍＡ和０．９７ｋＡ／ｃｍ＾２。     

Si/SiGe digital optoelectronic switch

The physical parameters and functional characteristics of a Si/SiGe digital optoelectronic switch are reported. The device is found to have bistable electrical states: a high-impedance (40 kΩ) OFF state connected to a low-impedance (100 Ω) ON state by a regime of negative differential resistance. The switching voltage and holding voltage are measured to be 2.6 and 1.3 V, respectively, and the switching current and holding current are measured to be 500 μA and 1 mA, respectively. These DC characteristics are found to be similar to those measured in double heterostructure optoelectronic switching devices manifested in the AlGaAs/GaAs materials system. The DC characteristics of this Si/SiGe digital optoelectronic switch are also found to be sensitive to optical input and temperature     

Si/SiGe heterostructure MITATT diode

The first experimental results on Si/SiGe heterostructure mixed tunnelling avalanche transit time (MITATT) diodes are reported. The layers are grown by MBE. At 103 GHz a very low noise CW output of 25 mW is obtained. With an optimisation of the design higher output powers with still low noise operation are expected     

Si/SiGe/SiHBT直流特性的可靠性

对单台面SiGeHBT在E-B结反偏应力下直流特性的可靠性进行了研究。研究结果表明,随应力时间的增加,开启电压增加,直流电流增益下降,特别是在低E-B正偏电压时下降明显;而交流电流增益退化缓慢。     

Time-resolved photoluminescence from self-assembled Ge(Si) islands in multilayer SiGe/Si and SiGe/SOI structures

The results of a study of the spectral and temporal characteristics of the photoluminescence (PL) from multilayer structures with self-assembled Ge(Si) islands grown on silicon and “silicon-on-insulator” substrates in relation to temperature and the excitation-light wavelength are presented. A substantial increase in island-related PL intensity is observed for structures with Ge(Si) islands grown on silicon substrates upon an increase in temperature from 4 to 70 K. This increase is due to the diffusion of nonequilibrium carriers from the silicon substrate into the active layer with the islands. In this case, a slow component with a characteristic time of ～100 ns appears in the PL rise kinetics. At the same time, no slow component in the PL rise kinetics and no rise in the PL intensity with increasing temperature are observed for structures grown on “silicon-on-insulator” substrates, in which the active layer with the islands is insulated from the silicon substrate. It is found that absorption of the excitation light in the islands and SiGe wetting layers mainly contributes to the excitation of the PL signal from the islands under sub-bandgap optical pump conditions.     

Intersubband lifetimes in Si/SiGe quantum wells

In the present work we report the first measurement of intersubband lifetimes in Si/Si_1−xGe_x quantum well samples. We have determined T₁ by a time resolved pump and probe experiment using the far infrared picosecond free electron laser source FELIX at Rijnhuizen, the Netherlands. In a sample with a well width of 50 Å and a sheet density of 2.1 × 10¹² cm⁻² we find a lifetime of 30 ps while 20 ps is observed for a density of 1.1 × 10¹² cm⁻² and a well width of 75 Å. We discuss acoustic phonon, as well as optical phonon intersubband scattering as possible limiting processes for the observed lifetimes in Si/SiGe and GaAs/AlGaAs quantum wells.     

Ultra flexible SiGe/Si/Cr nanosprings

The electrical and mechanical properties of Si/SiGe rolled-up nanosprings have been investigated. Micromanipulation has been employed to investigate the mechanical properties. For nanosprings under investigation, a linear dependence between applied force and extention is found until the spring is extended to 91% of its original length, moreover, the springs could be reproducibly extended to more than 180% of their original length. An extremely small spring constant of 0.003 N/m has been determined, which is an order of magnitude smaller than that of the most flexible available atomic force microscope (AFM) cantilever (～10^?2 N/m). Thus, it is expected that these springs can be used as ultra-sensitive force sensors. A simple estimation assuming an imaging resolution of approximately 1 nm is adopted for displacement measurement and reveals that using a nanospring fabricated from a 300 nm wide mesa as a visual-based force sensor, a resolution of 3 pN/nm can be provided. The conductivity of nanospirals was analysed and current densities up to 530 kA/cm² were measured. Structures with metallic wires on top of the mesa structures were successfully employed to activate mechanical movements of the structure.     

Growth of GaInP/GaAsP short period superlattices by flow modulation organometallic vapor phase epitaxy

One disadvantage of the GalnP/GaAs system is the difficulty often encountered in synthesizing the quaternary material GalnAsP, required to span the intermediate bandgap range (1.42–1.91 eV). Recent studies report on an extensive miscibility gap in this alloy. In this study, we investigate an alternative approach to the growth of material within this bandgap range. We have grown by flow-modulation organometallic vapor phase epitaxy, GalnP/GaAsP superlattices with periods ranging from 80 to 21Å. These are the first reported short-period superlattices in this material system. Effects of superlattice (SL) period, growth temperature, and phosphorous composition in the wells were studied by photoluminescence, high resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The effect of growth temperature on the structural quality of the SLs is correlated to ordering effects in the GalnP layers. Variations in the P composition and the SL period result in a shift in the room temperature bandgap emission from 1.51 to 1.74 eV. Strain-compensated structures have been realized by growing the SL barriers in compression.     

Study of threading dislocations in the plan-view sample of SiGe/Si(001) superlattices by transmission electron microscopy

Interfacial defects due to a mismatch of 1.378% between substrate and epilayer were examined in a Si_0.67Ge_0.33/Si(001) superlattice by transmission electron microscopy (TEM). Plan-view specimens from the superlattice were prepared to investigate the defects in the structure. It was observed that 60°C-type misfit dislocations associate with point contrast on and at their ends. This point contrast was found to represent threading dislocations by using tilt experiments in the microscope. Consequently, stereo electron microscopy was used to examine the threading dislocations. It was discovered that the threading dislocations are not on the {111} slip planes but can be almost parallel to the [001] zone axis.     

Infrared absorption in p-type SiGe/Si quantum wells: Intersubband transition and free carrier contributions

Infrared absorption has been investigated in high quality p-type SiGe/Si multiple quantum wells grown by UHV-CVD. Both intersubband and free carrier absorptions have been quantitatively analyzed using a modified Drude model, and their relative contributions to the total absorbance have been determined as a function of polarization and doping level. The absorption coefficients have been deduced for radiation electric field along the growth axis and parallel to the plane of the layers.     

Si／SiGe／Si双异质结晶体管异质结势垒效应（HBE）研究

本文研究了不同温度下Ｓｉ／ＳｉＧｅ／Ｓｉ双异质结晶体管异质结势垒效应，研究发现，集电结处价带能量差△Ｅｖ越大，ＨＢＥ越明显，在给定的△Ｅｖ下，随着温度的降低，ＨＢＥ越显著。     

Inversion-channel Si/SiGe heterojunction field-effect transistor

The p-channel operation of a selfaligned heterojunction field-effect transistor (HFET) based on an Si/Si/sub 0.75/Ge/sub 0.25/ heterostructure is demonstrated. Extrinsic transconductance g/sub m/ greater than 8 mS/mm for a device with 1 mu m gate length was measured at 300 K. The high frequency 3 dB point has been measured to be 1.8 GHz.<>