The integration of nanoscale porous silicon light emitters: materials science, properties, and integration with electronic circuitry

The stability, efficiency, speed, and spectral range of light-emitting devices (LEDs) made of nanoscale porous silicon is improving. The first part of this paper discusses the preparation and properties of nanoscale silicon, with emphasis on porous silicon. In the second part, the properties of LEDs made of porous silicon are reviewed. In the third part, the integration of PSi LEDs with silicon microelectronic circuits is discussed. The paper ends with a short discussion of the prospects for realistic optoelectronic devices.     

Growth peculiarities during vapor–liquid–solid growth of silicon nanowhiskers by electron-beam evaporation

One-dimensional (1D) silicon (Si) nanostructures were grown by electron-beam evaporation catalyzed by gold nanoparticles on silicon substrates following the vapor–liquid–solid growth mechanism. We report three strikingly different growth morphologies of the 1D Si nanostructures and discuss their formation. The morphology of the silicon nanostructures strongly depends on gold layer thickness, annealing temperature before deposition and growth temperature during the deposition. The formation of nanoscale silicon features such as nanobelts, nanowires and nanowhiskers was observed. The nanoscale silicon features were characterized by transmission and scanning electron microscopy using imaging, diffraction and energy-dispersive X-ray spectroscopy, atomic force microscopy and UV micro-Raman spectroscopy. PACS 68.37.Lp; 68.70.+w; 78.30.-j; 81.15.Jj     

Fabrication of freestanding nanoscale gratings on silicon-on-insulator wafer

We report a bottom-up process for the fabrication of freestanding nanoscale gratings on silicon-on-insulator (SOI) wafer. Freestanding membrane devices suffer deflection due to the residual stress of the buried oxide layer of SOI wafer. The deflection will affect the device shape and result in the fracture problem for devices fabricated on thin silicon membrane. The bottom-up process is developed to overcome the fabrication issue for thin silicon membrane gratings. The silicon handle layer is removed through back wafer etching of silicon, where the buried oxide layer acts as an etch stop layer. The grating structures are then defined on thin silicon device layer by electron beam lithography and generated by fast atom beam etching. The grating structures are finally released in vapor HF to form the freestanding nanoscale gratings. The freestanding linear/circular gratings, 1,500-nm period grating with the grating width of 200- and 850-nm period grating with the grating width of 100 nm, are successfully achieved on 260-nm silicon device layer.     

Construction and mechanism analysis on nanoscale thermal cloak by in-situ annealing silicon carbide film

In recent years,there is a strong interest in thermal cloaking at the nanoscale,which has been achieved by using graphene and crystalline silicon films to build the nanoscale thermal cloak according to the classical macroscopic thermal cloak model.Silicon carbide,as a representative of the third-generation semiconductor material,has splendid properties,such as the high thermal conductivity and the high wear resistance.Therefore,in the present study,we build a nanoscale thermal cloak based on silicon carbide.The cloaking performance and the perturbation of the functional area to the external temperature filed are analyzed by the ratio of thermal cloaking and the response temperature,respectively.It is demonstrated that silicon carbide can also be used to build the nanoscale thermal cloak.Besides,we explore the influence of inner and outer radius on cloaking performance.Finally,the potential mechanism of the designed nanoscale thermal cloak is investigated by calculating and analyzing the phonon density of states(PDOS)and mode participation rate(MPR)within the structure.We find that the main reason for the decrease in the thermal conductivity of the functional area is phonon localization.This study extends the preparation method of nanoscale thermal cloaks and can provide a reference for the development of other nanoscale devices.     

Silicon micro-hemispheres with periodic nanoscale rings produced by the laser ablation of single crystalline silicon

We describe the fabrication of silicon micro-hemispheres by adopting the conventional laser ablation of single crystalline silicon in the vacuum condition without using any catalysts or additives. The highly oriented structures of silicon micro-hemispheres exhibit many periodic nanoscale rings along their outer surfaces. We consider that the self-organized growth of silicon micro-structures is highly dependent on the laser intensity and background air medium. The difference between these surface modifications is attributed to the amount of laser energy deposited in the silicon material and the consequent cooling velocity.     

The effect of nitrogen incorporation on surface properties of silicon oxynitride films

In order to investigate the surface heterogeneity of silicon oxynitride films, we observed the nanoscale variation of the surface potential by Kelvin probe force microscopy (KFM), the molecular bonding characteristics by Fourier transform infrared spectrometry (FTIR), and the wetting behavior by contact angle measurement. Nitrogen incorporation into silicon oxynitride films influenced the decrease in the surface potential and the polar component of the surface free energy. We present the first correlation between the nanoscale measurement of the surface potential and the macroscopic measurement of the surface free energy in silicon oxynitride films grown by a standard plasma‐enhanced chemical vapor deposition (PECVD) technique. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nanoscale morphology dependent hydrogen coverage of meso-porous silicon

Hydrogen coverage of the specific surface of meso-porous silicon nanostructures is studied by means of attenuated total reflection infrared spectroscopy. A strong correlation of silicon hydride bonds and of total amount of the adsorbed hydrogen to the nanoscale morphology parameters such as porosity, nanocrystallites dimensions and fractal-like specific surface is reported.     

Effect of the parameters of pulsed anodic formation of porous silicon on its luminescent,paramagnetic, and electrotransport properties

We present the data on changes in the properties of porous silicon formed at the current pulse modulation in the range of 0.1–1 Hz with the aim to modulate the properties of porous silicon in a nanoscale range. It is demonstrated that the use of the pulsed mode of formation of porous silicon with a period of a few tenths of a second can dramatically affect the photoluminescence quantum yield and other properties of the material. There is a correlation of the luminescent, electrotransport, and paramagnetic properties of porous silicon formed under different modes.     

Characterization of silicon nanophotonic devices using the finite element method

The Poynting vector and the full-vectorial H and E-field profiles are considered for use in nanoscale silicon waveguides in this article. This paper reveals that the mode profile of a circular silicon nanowire is not circular and also has a strong axial field component. From the analysis, the characteristics of single mode operation and the vector field profiles of both circular and planar silicon nanowires are presented. The modal birefringence of rectangular silicon nanowires and power density in low-index region of a slot-type waveguide and designs of a compact polarization rotator are also presented in this work.     

Nanoscale volcanoes: accretion of matter at ion-sculpted nanopores

We demonstrate the formation of nanoscale volcano-like structures induced by ion-beam irradiation of nanoscale pores in freestanding silicon nitride membranes. Accreted matter is delivered to the volcanoes from micrometer distances along the surface. Volcano formation accompanies nanopore shrinking and depends on geometrical factors and the presence of a conducting layer on the membrane's back surface. We argue that surface electric fields play an important role in accounting for the experimental observations.     

Energy band and band-gap properties of deformed single-walled silicon nanotubes

The fantastic physical properties of single-walled silicon nanotubes (SWSiNTs) under mechanical strain make them promising materials for fabricating nanoscale electronic devices or transducers. Here we investigate the energy band and band-gap properties of the SWSiNTs calculated from the tight-binding model approximation. The results show that the band-gap properties are very sensitive to the deformation degree and the helicity of the SWSiNTs. The results can be employed to guide the design of nanoelectronic devices based on silicon nanotubes.     

Model of silicon carbide formation on porous substrates

The formation of thin silicon carbide layers as a result of solid-phase processes is related to the evolution of nanoscale porosity and chemical reactions on pore surfaces. Numerical experiments, which simulate blistering under the action of Xe+ ions in the metal-insulator (Mo/Si) bilayer make it possible to establish the relationship between the porosity parameters and layer stresses and the irradiation conditions. Similar patterns in the formation of defects (pores and cracks) in crystalline silicon characterize its interaction with carbon dioxide when silicon carbide is formed. The calculated characteristics of the nucleation in the Mo/Si bilayers are analyzed to optimize the solid-phase epitaxy of silicon carbide.     

Energy band and band-gap properties of deformed single-walled silicon nanotubes

The fantastic physical properties of single-walled silicon nanotubes (SWSiNTs) under mechanical strain make them promising materials for fabricating nanoscale electronic devices or transducers. Here we investigate the energy band and band-gap properties of the SWSiNTs calculated from the tight-binding model approximation. The results show that the band-gap properties are very sensitive to the deformation degree and the helicity of the SWSiNTs. The results can be employed to guide the design of nanoelectronic devices based on silicon nanotubes.     

单晶硅薄膜法向热导率分子动力学研究

采用非平衡分子动力学方法（NEMD）研究了平均温度为 500K、厚度为 2～32nm的单晶硅薄膜的法向热导率。模拟结果表明,薄膜热导率显著低于对应温度下的体硅单晶的实验值,并随膜厚度减小以接近线性的规律减小。用声子气动力论模型的分析结果与NEMD模拟相一致,表明纳米单晶硅薄膜中声子平均自由程显著减小。     

Atom probe tomography of size‐controlled phosphorus doped silicon nanocrystals

Doping of silicon nanocrystals is essential to control their electronic and optical properties. The incorporation of an impurity into a silicon nanovolume is a nontrivial task due to the self‐purification effect. Here, a systematic atom probe tomography study of the phosphorus distribution and incorporation in size‐controlled silicon nanocrystals embedded in silicon dioxide is presented. Qualitatively, it turns out that the phosphorus distribution in the system follows a universal, nanocrystal‐size independent trend: phosphorus‐enrichment at the interface with a substantial phosphorus‐incorporation in the silicon nanocrystal as small as 2 nm in diameter. This clearly contradicts strict self‐purification. These observations are explained by the bulk‐solubility and ‐segregation behaviour, kinetic effects related to the diffusion lengths, and nanoscale interface strain. The quantitative determination of the amount of phosphorus atoms per quantum dot enables a systematic understanding of phosphorus‐induced effects on optical and electronic properties of silicon nanovolumes.     

Graphene-based nano-patch antenna for terahertz radiation

The scattering of terahertz radiation on a graphene-based nano-patch antenna is numerically analyzed. The extinction cross section of the nano-antenna supported by silicon and silicon dioxide substrates of different thickness are calculated. Scattering resonances in the terahertz band are identified as Fabry–Perot resonances of surface plasmon polaritons supported by the graphene film. A strong tunability of the antenna resonances via electrostatic bias is numerically demonstrated, opening perspectives to design tunable graphene-based nano-antennas. These antennas are envisaged to enable wireless communications at the nanoscale.     

硅纳米薄膜法向热导率的进一步分析

应用非平衡分子动力学方法进一步研究了平均温度为300K、厚度为2.715nm-43.44nm的单晶硅薄膜的法向热导率,模拟结果表明,薄膜热导率低于同温度下单晶硅的实验值,存在显著的尺寸效应,当膜厚度在20nm以下时,法向热导率随尺度减小而线性减小,当膜厚度大于20nm时法向热导率随尺度呈现二阶多项式变化。法向热导率的变化规律与面向热导率的变化规律类似,表明薄膜厚度和表面晶格结构对声子传热影响的复杂性。     

Mechanism for the Correlated Swinging of Photoluminescence Intensity and Peak Energy Shift with Sizes of Nanoscale Si Particles

Based on the quantum confinement-luminescence center model, we focus on the relationship between the photoluminescence (PL) spectra and sizes of nanoscale silicon particles.We find that when there are two kinds of luminescence centers (LC) in the oxide layer surrounding the silicon particles, both the integrated PL intensity and the spectral peak position swing with reducing the sizes of silicon particles, which is different from the monotonous blueshift of peak position predicted by quantum confinement model. By changing the concentrations of LC we find the correlation between the spectral peak position and the integrated PL intensity when the size of silicon particles is reduced. The effects of other parameters such as the half width of size distribution and the position of photon emission levels of LC are also found to be important.     

Performance investigation of nanoscale thermal cloak by the perforated silicon film

In recent years, nanoscale thermal cloak, as a representative of nanoscale heat flux regulation devices, has attracted a lot of attention from researchers. However, the existing design methods are relatively complicated and all adopt constant temperature boundaries, the temperature changes constantly in the real environment, which greatly hinders its engineering applications. In this paper, inspired by phonon localization theory, we construct a nanoscale thermal cloak by a perforated silicon membrane and evaluate its cloaking performance and dynamic response. Results show that when the perforated area is fixed, the more the number of holes, the better the cloaking performance. In addition, the nanoscale thermal cloak still exhibits good cloaking performance in the dynamic environment. Finally, the cloaking mechanism is analyzed by calculating the phonon density of states (PDOS) and mode participation rate (MPR), and the reduction of thermal conductivity in the functional region is attributed to phonon localization.     

Bismuth onion thin film in situ grown on silicon wafer synthesized through a hydrothermal approach

Bismuth onion structured nanospheres with the same structure as carbon onions have been synthesized and observed. The nanospheres were synthesized through a hydrothermal method using bismuth hydroxide and silicon wafer as reactants. By controlling the heating temperature, heating time, and the pressure, nanoscale bismuth spheres can be in situ synthesized on silicon wafer, and forms a bismuth onion film on the substrate. The electronic property of the films was investigated. A formation mechanism of the formation of bismuth onions and the onion film has been proposed on the basis of experimental observations.