Electrical peculiarities in Al/Si/Ge/…/Ge/Si and Al/SiGe/Si structures

The current–voltage (I–V) and capacitance–voltage (C–V) behaviour of different Si/Ge multilayers and SiGe single layers prepared on p-type Si substrates by magnetron sputtering and annealing, has been studied in the temperature range of 80–320 K by using Al Schottky contacts as test structures. Although a significant influence of the microstructure of the Si/Ge multilayers and SiGe layers was obtained on the electrical behaviour of the structures, the structures exhibited similar specific features.     

Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

Vertical conduction in thin Si/CaF2/Si structures

Electrical characteristics of thin (∼100Å), single barrier Si/CaF₂/Si heterostructures have been measured for the first time for both A and B phase CaF₂. I(V,T) measurements for different thickness CaF₂ barriers show characteristics that are consistent with conduction through defect sites in the CaF₂ layer. The B-phase CaF₂ exhibits far more defects than the A -phase material. Measurements of different size mesas indicate a defect density on the order of one per 1000μm² in the 100Å barrier thickness A-phase material.     

Electronic Structure of Si1-xⅣx/Si Superlattices on Si （001）

We have preformed systematical ab initio studies of the structural and electronic properties of short-period Si1-xⅣx/Si （x = 0.125, 0.25, 0.5, Ⅳ=Ge, Sn） superlattices （SLs） grown along the [001] direction on bulk Si. The present calculations reveal that the Si0.875Ge0.125/Si, Si0.75Ge0.25/Si and Si0.875Sn0.125/Si are the F-point direct bandgap semiconductors. The technological importance lies in the expectation that the direct gap Si1-xⅣx/Si SLs may be used as components in integrated optoelectronic devices, in conjunction with the already well-established and highly advanced silicon technology.     

Dipolar Biexcitons in Lateral Traps in Si/SiGe/Si Heterostructures

Si/Si_1–xGe_x/Si heterostructures with large-scale (micrometer-size) lateral potential fluctuations at the upper SiGe/Si-cap heterointerface are grown. These potential fluctuations are caused by partial strain relaxation in the SiGe layer. Low-temperature photoluminescence (PL) spectra show that these fluctuations form lateral traps where photoexcited nonequilibrium charge carriers are accumulated and bind into dipolar excitons, which ultimately recombine. At temperatures below 6 K, a new narrow line with a width considerably less than that of the dipolar exciton PL line emerges in the spectra as the level of excitation increases. It is shown that this line is associated with the recombination of dipolar biexcitons in large-scale traps.     

IR Transmittance of Si/SiO2/Si3N4/Si Insular Structures Formed by Selective Laser Annealing

Journal of Applied Spectroscopy - Periodic Si/SiO2/Si3N4/Si structures with an insular surface layer were formed by selective laser annealing. A study by Fourier infrared spectrometry in the range...     

Thermal behaviour of Co/Si/W/Si multilayers under rapid thermal annealing

The e-beam deposited multilayers (MLS) were studied under rapid thermal annealing (RTA) between 250°C and 1000°C during 30 s. MLS with five Co/Si/W/Si periods, each 13.9 nm (MLS1) and 18 nm (MLS2) were deposited onto oxidized Si substrates. Samples were analyzed by X-ray diffraction, hard and soft X-ray reflectivity measurements and grazing incidence X-ray diffuse scattering. The MLS period, interface roughness and its lateral and vertical correlations were obtained by simulation of the hard X-ray reflectivity and diffuse scattering spectra. The MLS1 with thinner Co layers is more temperature resistant. However, its soft X-ray reflectivity is smaller. The results show that this is because of shorter lateral and vertical correlation lengths of the interface roughness which may considerably influence the X-ray reflectivity of multilayers.     

Fundamental processes in Si/Si and Ge/Si epitaxy studied by scanning tunneling microscopy during growth

Experimental results on the epitaxy of Si and Ge on Si(0 0 1) and Si(1 1 1) surfaces, which are obtained by scanning tunneling microscopy (STM) imaging during growth, are reviewed. Techniques for simultaneous epitaxial growth and STM measurements at high temperature are described. The ability to access the evolution of the growth morphology during growth down to the atomic level enables the study of the influence of surface reconstruction on the growth. The relatively complete characterization of the growth process facilitates comparison to theoretical models and allows the identification of fundamental growth processes. For instance, the observed transition between different growth modes can be explained by specific growth processes included in a model. The influence of strain on the growth morphology is reviewed for the case of heteroepitaxial growth of Ge on Si. With the method of combining STM imaging and epitaxial growth, the transition from two-dimensional to three-dimensional growth as well as the evolution of size and shape of three-dimensional islands can be studied.     

Phase transitions in nonequilibrium electron-hole systems of Si/SiGe/Si nanoheterostructures

The exciton condensation in a Si_1?x Ge _x solid solution layer of Si/Si_1?x Ge _x /Si heterostructures with the formation of electron-hole liquid has been investigated by low-temperature photoluminescence spectroscopy. In the temperature range above the critical temperature of the transition from an exciton gas to electron-hole liquid, a Mott transition from an exciton gas to electron-hole plasma has been found and investigated.     

Realization of silicon quantum wires based on Si/SiGe/Si heterostructure

We report on the successful fabrication of silicon quantum wires with SiO2 boundaries on SiGe/Si heterostructures by combining Si/SiGe/Si heteroepitaxy, selective chemical etching, and subsequent thermal oxidation. The observational result of scanning electron microscope is demonstrated. The present method provides a well-controllable way to fabricate silicon quantum wires.     

Optical modulator based on a Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice structure

An optical modulator is designed and fabricated based on a Si_0.75Ge_0.25/Si/Si_0.5Ge_0.5 asymmetrical superlattice structure. The device comprises a p-i-n diode made on the asymmetrical superlattice integrated with a 920-μm-long Fabry-Perot (F-P) cavity. Parameters of the rib waveguide are designed to satisfy only the fundamental-TE mode transmission. Here, 65 and 40-pm red shifts of the peak resonant were measured under the applied bias of 2.5 and ?32.0 V, respectively. The analysis shows that, besides the thermal-optical and plasma dispersion effects, the Pockels effect also contributes to such a peak shift. The corresponding calculated effective Pockels coefficient is about 0.158 pm/V.

     

Photoconductivity of Si/Ge/SiO<Subscript>x</Subscript> and Si/Ge/Si structures with germanium quantum dots

A nonmonotonic dependence of the lateral photoconductivity (PC) on the interband light intensity is observed in Si/Ge/Si and Si/Ge/SiO_x structures with self-organized germanium quantum dots (QDs): in addition to a stepped increase in PC, a stepped decrease in PC is also observed. The effect of temperature and drive field on these features of the PC for both types of structures with a maximum nominal thickness of the Ge layer (N_Ge) is studied. The results obtained are discussed in the context of percolation theory for nonequilibrium carriers localized in different regions of the structure: electrons in the silicon matrix and holes in QDs.     

硅化物薄膜的质子弹性散射分析

本文报道了一种分析硅衬底上SiN_x和SiO_x的N/Si和O/Si含量比的简便方法。用1.95MeV质子弹性散射测量薄膜(9000—15000)的组分比和厚度,实验值与2.1MeVHe的背散射分析(RBS)结果符合得很好;对微米以上厚度样品,MeVH束分析更为有利,这是与He束背散射分析互补的一种方法。文中给出了实验结果,并进行了讨论。 关键词：     

金属/多孔硅/单晶硅(M/PS/Si)微结构的电学特性

采用双槽电化学腐蚀法制备多孔硅层,然后在多孔硅表面沉积形成金属电极,制备出M/PS/Si微结构.利用SEM分析多孔硅的表面形貌,通过测试其I-V特性分析M/PS/Si微结构的电学特性.结果表明:由Pt做电极形成的M/PS/Si结构,表现出非整流特性.M/PS/Si结构的I-V曲线由线性区和非线性区组成,多孔硅孔隙率越高的M/PS/Si结构的I-V特性曲线线性区越宽.由Cu做电极形成的M/PS/Si结构,表现出整流特性.其整流比随多孔硅孔隙率增加而减小. 关键词： M/PS/Si微结构 孔隙率 I-V特性')" href="#">I-V特性 欧姆接触     

Thermoelectric transport in strained Si and Si/Ge heterostructures

The anisotropic thermoelectric transport properties of bulk silicon strained in the [111]-direction were studied by detailed first-principles calculations focusing on a possible enhancement of the power factor. Electron and hole doping were examined in a broad doping and temperature range. At low temperature and low doping an enhancement of the power factor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. For the thermoelectrically more important high-temperature and high-doping regime a slight enhancement of the power factor was only found under small compressive strain with the power factor overall being robust against applied strain. To extend our findings the anisotropic thermoelectric transport of a [111]-oriented Si/Ge superlattice was investigated. Here, the cross-plane power factor under hole doping was drastically suppressed due to quantum-well effects, while under electron doping an enhanced power factor was found. For this, we state figures of merit of ZT?=?0.2 and 1.4 at T?=?300?and 900?K for the electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in terms of band structure features.     

硅基超晶格Si1-xSnx/Si的能带结构

由于Si基发光材料能与现有的Si微电子工艺兼容,其应用前景被广泛看好. 设计具有直接带隙的Si基材料,备受实验和理论研究者的关注. 本文根据芯态效应、电负性差效应和对称性效应设计了Si基超晶格Si_1－xSn_x/Si. 其中Si_0.875Sn_0.125/Si为直接带隙材料. 在密度泛函框架内,采用平面波赝势法计算表明,Si_0.875Sn_{0.125相似文献}   

Simulation of range profiles for boron implantation into SiO2/Si and Si3N4/SiO2/Si targets

The simple method of profile combination is shown to be applicable to the simulation of boron profiles in SiO₂/Si and Si₃N₄/Si layered targets. This is demonstrated by comparison with range distributions calculated by more sophisticated theoretical methods, i.e. TRIM Monte Carlo simulations and the algorithm of Christel et al., and with experimental data. The method of profile combination can also be applied to layered targets with a crystalline silicon substrate.     

Luminescence and electrical properties of diode Si/SiGe:Er/Si heterostructures

The diode Si/Si_{1 ? x} Ge _x :Er/Si heterostructures grown by sublimation molecular-beam epitaxy in a german atmosphere have been investigated. The electrical properties of Si_{1 ? x} Ge _x :Er heterolayers, the currentvoltage characteristics of the structures, and their photo-and electroluminescent properties in the forward-and reverse-bias modes have been analyzed. A relationship is established between the heterolayer parameters and the luminescence response features and characteristics of diode structures.     

Leakage current and capacitance characteristics of Si/SiO2/Si single-barrier varactor

We investigate, both experimentally and theoretically, current and capacitance (I–V/C–V) characteristics and the device performance of Si/SiO₂/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO₂ layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currents (about 5×10^-2 and 1.8×10^-2 mA/mm²) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm² for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm² device area, 760-μm modulation layer thickness and ≈10¹⁵-cm^-3 doping level), the estimated cut-off frequency is about 5×10⁷ Hz. With the physical parameters of the present existing III–V triplers, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz. Received: 9 February 2001 / Accepted: 9 February 2001 / Published online: 23 March 2001