Si／Si1—xGexHEMT结构设计的研究

从晶格匹配及能带阶跃角度讨论了n沟Si/Si1-xGexHEMT结构的设计原理及方法,对Ismail器件进行了分析和计算,所得二维电子气（2DEG）的n3与实验结果基本相符,并利用该设计理论对Ismail器件的异质结结构进行了优化改进,提高了器件2DEG的ns。     

能隙阶梯缓变结构Si1-xGex/Si光电探测器

提出了一种新结构Ｓｉ１－ｘＧｅｘ／Ｓｉ光电探测器－能隙阶梯缓变结构的Ｓｉ１－ｘＧｅｘ／ＳｉＰＩＮ新近红外光电探测器。理论分析表明,能隙缓变增大了载流子的离化率。价带的不连续则有利于空穴离化,从而对载流子的收集有利,可获得高的光电响应。实验结果表明,该探测器具有良好的Ｉ－Ｖ特性,反向漏电低达０．１μＡ／ｍｍ＾２（－２Ｖ。该探测器主峰值波长在０．９６μｍ。其光电流响应随着反应偏压的增加有明显的增大,在     

Anomalous coiling of SiGe/Si and SiGe/Si/Cr helical nanobelts

The fabrication of nanohelices by the scrolling of strained bilayers is investigated. It is shown that structure design is dominated by edge effects rather than bulk crystal properties such as the Young's modulus when the dimensions of the structures are reduced below 400 nm. SiGe/Si/Cr, SiGe/Si, and Si/Cr helical nanobelts are used as test structures. Dimensions of the belt width are reduced from 1.30 microm to 300 nm, and parameters controlling helicity angle, chirality, diameter, and pitch of the nanohelices are investigated. An anomalous scrolling direction deviating from the preferred <100> scrolling direction has been found for small structures. Making use of the anomalous scrolling, it is possible to fabricate three-dimensional helices with helicity angles less than 45 degrees , which is advantageous for micro- and nanoelectromechanical systems.     

Thickness effect on the formation of SiC nanoparticles in sandwiched Si/C/Si and C/Si multilayers

The effect of carbon (C) and amorphous silicon (a-Si) thicknesses on the formation of SiC nanoparticles (np-SiC) in sandwiched Si/C/Si and C/Si multilayers on Si(100) substrates were investigated using ultra-high-vacuum ion beam sputtering system and vacuum thermal annealing at 500, 700, 900 °C for 1.0 h. Three-layer a-Si/C/a-Si structures with thicknesses of 50/200/50 nm and 75/150/75 nm and a two-layer C/a-Si structure of 200/50 nm were examined in this study. The size and density of np-SiC were strongly influenced by the annealing temperature, a-Si thickness and layer number. Many np-SiC appeared at 900 °C at a density order about 10⁸ cm^− 2 in both three-layer structures while no particles formed in the two-layer structure. The thick a-Si structure (75/150/75 nm) produces a particle density approximately 1.8 times higher than thin structure (50/200/50 nm). This implies that thick a-Si structure had a lower activation energy of SiC formation compared to the thin a-Si structure. Few particles were found at 700 °C and no particles at 500 °C in both three-layer structures. The np-SiC formation is a thermally activated reaction. The higher temperature leads to higher particle density. A mechanism of np-SiC formation in thermodynamic and kinetic viewpoints is proposed.     

Mg2Si／Si异质结的制备

采用射频磁控溅射和低真空退火方法制备Mg2Si／Si异质结,首先在n型Si（111）衬底上沉积Mg膜,经低真空退火形成Mg2Si／Si异质结,Mg膜厚度约为484nm,退火后形成的Mg2Si薄膜厚度约400nto,利用xRD和sEM分别研究了Mg2Si薄膜的晶体结构和表面形貌,霍尔效应结果表明,制备的Mg2Si薄膜呈现n型导电特性。     

Investigation of Si and Ge growth on Si3N4/Si

The growth of Si and Ge on silicon nitride surfaces has been investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectrometer (AES). In the early stages, Si or Ge nanoclusters appeared irrespective of the different substrates. When annealed, the Si clusters were more stable against coalescence than those of Ge. As these clusters continued to grow, crystalline facets started to form. Both Si and Ge islands grew predominantly with (111)-oriented top facets on the crystalline Si₃N₄(0001)/Si(111). By contrast, they both grew in random orientation on the amorphous Si₃N₄ surface. Low-index facets such as (111) and (001) coexisted with high-index facets such as (113).     

Physics and applications of Si/SiGe/Si resonant interband tunneling diodes

Room temperature (RT) current–voltage characteristics of Si/Si_1−xGe_x/Si p⁺-i-n⁺ interband tunneling diodes are presented. The variation of the structural properties results in a more detailed picture of the tunneling process in these diodes, which allows further improvement of the relevant parameter. Special attention is paid to the peak current density (PCD) and the peak-to-valley current ratio (PVCR) of the devices. For an optimized structure with a 3-nm thick Si_0.54Ge_0.46 layer in the intrinsic zone a record PVCR of 6.0 at a PCD of approximately 1.5 kA/cm² was achieved. By reducing the layer thickness to 2.6 nm and simultaneously increasing the Ge content to 54%, the PCD increases to 30 kA/cm² at a high PVCR of 4.8.     

Growth of nickel silicides in Si and Si/SiOx core/shell nanowires

We exploited the oxide shell structure to explore the structure confinement effect on the nickel silicide growth in one-dimensional nanowire template. The oxide confinement structure is similar to the contact structure (via hole) in the thin film system or nanodevices passivated by oxide or nitride film. Silicon nanowires in direct contact with nickel pads transform into two phases of nickel silicides, Ni31Si12 and NiSi2, after one-step annealing at 550 °C. In a bare Si nanowire during the annealing process, NiSi2 grows initially through the nanowire, followed by the transformation of NiSi2 into the nickel-rich phase, Ni31Si12 starting from near the nickel pad. Ni31Si12 is also observed under the nickel pads. Although the same phase transformations of Si to nickel silicides are observed in nanowires with oxide confinement structure, the growth rate of nickel silicides, Ni31Si12 and NiSi2, is retarded dramatically. With increasing oxide thickness from 5 to 50 nm, the retarding effect of the Ni31Si12 growth and the annihilation of Ni2Si into the oxide confined-Si is clearly observed. Ni31Si12 and Ni2Si phases are limited to grow into the Si/SiOx core-shell nanowire as the shell thickness reaches 50 nm. It is experimental evidence that phase transformation is influenced by the stressed structure at nanoscale.     

Ni-silicide growth kinetics in Si and Si/SiO2 core/shell nanowires

A systematic study of the kinetics of axial Ni silicidation of as-grown and oxidized Si nanowires (SiNWs) with different crystallographic orientations and core diameters ranging from ～ 10 to 100 nm is presented. For temperatures between 300 and 440?°C the length of the total axial silicide intrusion varies with the square root of time, which provides clear evidence that the rate limiting step is diffusion of Ni through the growing silicide phase(s). A retardation of Ni-silicide formation for oxidized SiNWs is found, indicative of a stress induced lowering of the diffusion coefficients. Extrapolated growth constants indicate that the Ni flux through the silicided NW is dominated by surface diffusion, which is consistent with an inverse square root dependence of the silicide length on the NW diameter as observed for (111) orientated SiNWs. In situ TEM silicidation experiments show that NiSi(2) is the first forming phase for as-grown and oxidized SiNWs. The silicide-SiNW interface is thereby atomically abrupt and typically planar. Ni-rich silicide phases subsequently nucleate close to the Ni reservoir, which for as-grown SiNWs can lead to a complete channel break-off for prolonged silicidation due to significant volume expansion and morphological changes.     

Growth mechanism of epitaxial CoSi2 on Si and reactive deposition epitaxy of double heteroepitaxial Si/CoSi2/Si

The growth mechanism of epitaxial CoSi₂ was studied using Co/Ti/Si multilayer solid phase reaction. Results showed that phase formation was controlled by diffusion of Co through the growing CoSi_x, although at the early stage of CoSi₂ growth the diffusion of Co could be controlled by a Ti layer. A reactive deposition technique was also evaluated by using a conventional magnetron sputtering system. Results showed that an epitaxial CoSi₂ layer was formed by controlling the Co sputtering rate not to exceed the Co diffusion rate through CoSi_x. However, the surface of CoSi₂ became rough when the deposition rate was much slower than the Co diffusion rate through CoSi_x. The roughness was caused by the formation of CoSi₂ (111) facets at the interface between CoSi₂ and the Si substrate. Si/CoSi₂/Si double heteroepitaxial structures were fabricated when Si and Co were sequentially sputter-deposited on a Si (100) substrate.     

Effect of vacuum annealing on the phase composition of In/SnO/Si, In/SnO2/Si, and Sn/In2O3/Si heterostructures

The chemical interaction between indium and thin SnO and SnO₂ films and between tin and thin In₂O₃ films during vacuum annealing was studied. The metallic films were deposited onto single-crystal silicon substrates by magnetron sputtering, the SnO and SnO₂ films were produced by heat-treating the Sn film in flowing oxygen at 673 and 873 K, respectively, and the In₂O₃ film was produced by heat-treating the In film at 573 K. The results indicate that annealing of the In/SnO/Si and In/SnO₂/Si heterostructures in vacuum (residual pressure of 0.33 × 10^?2 Pa) at 773 K gives rise to the reduction of Sn and oxidation of In, whereas annealing of Sn/In₂O₃/Si causes partial tin substitution for indium in the cubic indium oxide lattice.     

Effect of strong illumination on current-voltage characteristics of Au/Si, Al/Si and Sn/Si Schottky barriers with native oxide layer

Light induced general degradation in the dark I–V characteristics of Au/Si, Al/Si and Sn/Si junctions at low temperature and at room temperature. Illumination caused changes in the interface and bulk properties of the investigated junctions, all of them prepared under identical conditions. Their barrier heights, φB change with increasing illumination time. The largest rate of degradation in φB upon exposure to light was observed for an Sn/Si junction (lowest φB), whereas the smallest change occurred with an Au/Si junction (highest φB). At low temperature, upon turning off the light, the photogenerated current of the Sn/Si sample exhibited faster recovery in reaching the initial dark current (at till=0) than the Al/Si junction; for the less reactive Au/Si sample, the presence of the oxide layer reduced the leakage current and subsequently delayed recovery of the measured photocurrent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of UV Irradiation on the Kinetics of Annealing-Induced Phase Transformations in Ti/Si, V/Si, and Zr/Si Heterostructures

The effect of irradiation at = 312.5, 365.0, and 552.0 nm on annealing-induced phase transformations and electrical properties of Ti/Si, V/Si, and Zr/Si heterostructures is studied. The results demonstrate that irradiation at these wavelengths during annealing offers the possibility of obtaining different metal oxides and silicides, depending on the treatment conditions.     

PECVD SiO2/Si3N4双层膜驻极体性能

本文研究了在带有Cr/Au电极的玻璃衬底上利用PECVD制备的SiO2/Si3N4双层膜驻极体性能.针对这种驻极体提出了一个简单的工艺流程暴露出一部分金属电极,并在电晕注极过程中将底电极引出接地.通过实验改变电晕注极过程中的注极时间、温度等因素,希望得到对PECVD制备的SiO2/Si3N4双层膜驻极体性能的优化.本文证实了PECVD双层膜具备良好的驻极体性能,有望广泛应用于微器件中.     

Al/Si contacting of ultra-shallow epitaxially grown Si and SiGe junctions

Ultra-shallow diodes have been fabricated by epitaxially growing thin layers of highly doped Si or strained SiGe on silicon substrate wafers and contacting with Al/1%Si. Ideal diode I –V characteristics were achieved for both n⁺p and p⁺n junctions as shallow as 20 nm. The formation of silicon precipitates on the contact surface as a result of alloying after metallization was found to be impeded by increasing the Ge content of the epitaxially grown layer. For a concentration of 27%, no precipitates were observed.     

One-step Ge/Si epitaxial growth

Fabricating a low-cost virtual germanium (Ge) template by epitaxial growth of Ge films on silicon wafer with a Ge(x)Si(1-x) (0 < x < 1) graded buffer layer was demonstrated through a facile chemical vapor deposition method in one step by decomposing a hazardousless GeO(2) powder under hydrogen atmosphere without ultra-high vacuum condition and then depositing in a low-temperature region. X-ray diffraction analysis shows that the Ge film with an epitaxial relationship is along the in-plane direction of Si. The successful growth of epitaxial Ge films on Si substrate demonstrates the feasibility of integrating various functional devices on the Ge/Si substrates.     

SiGe/Si异质结光电器件

SiGe/Si异质结光电器件及其光电集成(OEIC)是硅基光电研究的一个非常引人注目的领域.综述了SiGe/Si异质结材料的基本性质,SiGe/Si异质结光电器件的结构、性能、应用及其光电集成.重点介绍了SiGe/Si光电探测器及其与其他相关器件的集成.     

Optoelectronic aspects of strained Si1−xGex/Si quantum wells

Optical properties of molecular beam epitaxially grown strained Si_1–xGe_x/Si quantum wells (QWs) are described highlighting their potentials to optoelectronics applications. Fundamentals regarding luminescence properties associated with Si-lattice-mathced strained Si_1–xGe_x/Si QWs and their allied extended structures are described, followed by demonstration of challenges in the context of materials growth and quantum electronics with primary focus on light emitter fabrication.     

Field effect on electron-hole recombination in Si/Si1−xGex/Si quantum wells having a W-like type II potential profile

A theoretical analysis, using a Schrödinger solver, is made to calculate the electric field-dependent interband transitions in a Si/Si_1−xGe_x/Si double QW strain-compensated in relaxed Si_1−yGe_y barriers. The conduction and the valence band present a W-like potential profile, resulting in a quasi-type I heterostructure. Three peculiar features are revealed as the electric field is increased: (i) two uncoupled e₁₁ and e₁₂ electron levels are generated, (ii) the e₁₁–hh₁ fundamental transition due to first silicon QW exhibits a red shift in emission energy while the e₁₂–hh₁ transition energy is bleu shifted, (iii) an improved wave function overlap for the e₁₁–h₁ fundamental transition, the latter property showing the advantage having two adjacent QWs in this W architecture.