氧化锌/硅纳米孔柱阵列的结构和光致发光特性研究

以硅纳米孔柱阵列(Si-NPA)为衬底、用化学气相沉积法制备了具有规则阵列结构特征的ZnO/Si-NPA纳米复合体系，并对其结构和光致发光性质进行了表征. 实验结果显示，组成ZnO/Si-NPA表面阵列的每个柱子均呈现层壳结构. 不同于衬底Si-NPA的红光和蓝光发射，ZnO/Si-NPA在紫外光区和蓝绿光区呈现出两个强的宽发光峰. 分析表明，紫外光发射应归因于ZnO晶体的带边激子跃迁；而蓝绿光发射则来自于ZnO晶体本征缺陷所形成的两类深能级复合中心上载流子的辐射跃迁.     

Preparation, structural and electrical properties of zinc oxide grown on silicon nanoporous pillar array

Polycrystalline thick film of zinc oxide (ZnO) is grown on a unique silicon substrate with a hierarchical structure, silicon nanoporous pillar array (Si-NPA), by using a vapour phase transport method. It is found that as-grown ZnO film is composed of closely packed ZnO crystallites with an average size of $\sim$10\,\mu$m. The film resistivity of ZnO/Si-NPA is measured to be $\sim$8.9\Omega\cdot$\,cm by the standard four probe method. The lengthwise $I$-$V$ curve of ZnO/Si-NPA heterostructure is measured. Theoretical analysis shows that the carrier transport across ZnO/Si-NPA heterojunction is dominated by two mechanisms, i.e. a thermionic process at high voltages and a quantum tunnelling process at low voltages.     

银/硅纳米孔柱阵列活性基底的SERS效应研究

以硅纳米孔柱阵列(Si-NPA)为衬底,采用浸渍法制备出一种具有规则表面形貌特征的银/硅纳米孔柱阵列(Ag/Si-NPA),并以R6G为探测目标材料,对其表面增强拉曼(SERS)效应进行了研究。结果表明,对于R6G浓度低至10-15M,Ag/Si-NPA均能表现出清晰的特征SERS峰。随着浓度的降低,R6G的荧光淬灭,所测拉曼光谱的基线降低,但特征峰峰位基本保持不变。在低浓度10-15M时得到的SERS光谱,理论上证明为单分子光谱。此外,Ag/Si-NPA活性基底具有较好的稳定性,在长达28天的自然老化过程中,Ag/Si-NPA能够保持对R6G较高的探测水平,光谱具有较好的信噪比和分辨率。Ag/Si-NPA是一种理想的SERS活性基底。     

Structure transition and photoluminescence of CdS/Si nanoheterostructure array on thermal annealing

CdS/Si heterojunctions have been prepared through growing CdS nanocrystallites (nc-CdS) on the silicon nanoporous pillar array (Si-NPA) by the chemical bath deposition method. Cadmium nanocrystallites (nc-Cd) have been observed and ascribed to the reducibility of Si-NPA. The reason for the appearance of CdO is indistinct and the related work will be done in the future. The blue, green and red emissions are ascribed to the silicon oxide layer, band gap of nc-CdS and the sulphur vacancies, respectively. Redshift and blueshift with the annealing temperature about green emissions are contributed to quantum size effect and the structure transition from nc-Cd to CdO. It is beneficial for investigating the structures and defects to the application of CdS/Si in the optoelectronic field.     

Breakdown characteristics of AIGaN/GaN Schottky barrier diodes fabricated on a silicon substrate

In this work, the breakdown characteristics of AlGaN/GaN planar Schottky barrier diodes （SBDs） fabricated on the silicon substrate are investigated. The breakdown voltage （BV） of the SBDs first increases as a function of the anodeto-cathode distance and then tends to saturate at larger inter-electrode spacing. The saturation behavior of the BV is likely caused by the vertical breakdown through the intrinsic GaN buffer layer on silicon, which is supported by the post-breakdown primary leakage path analysis with the emission microscopy. Surface passivation and field plate termination are found effective to suppress the leakage current and enhance the BV of the SBDs. A high BV of 601 V is obtained with a low on-resistance of 3.15 mΩ·cm^2.     

A prototype silicon detector system for space cosmic-ray charge measurement

A readout electronics system used for space cosmic-ray charge measurement for multi-channel silicon detectors is introduced in this paper, including performance measurements. A 64-channel charge sensitive ASIC （VA140） from the IDEAS company is used. With its features of low power consumption, low noise, large dynamic range, and high integration, it can be used in future particle detecting experiments based on silicon detectors.     

High-efficiency focusing grating coupler with optimized ultra-short taper

A novel high-efficiency focusing non-uniform grating coupler is proposed to couple light into or off silicon photonic chips for large-scale silicon photonic integration. This kind of grating coupler decreases the transition length of the linking taper between the grating and the single-mode waveguide by at least 80%. The radian of the grating lines and the size of the taper are optimized to improve the coupling efficiency. An experimental coupling efficiency of ~ 68% at 1556.24 nm is obtained after optimization and the whole size of the grating is 12 μm × 30 μm, with a very short taper transition of ~15 μm long.     

On-chip optical pulse shaper for arbitrary waveform generation

We propose and demonstrate a silicon-on-insulator(SOI) on-chip optical pulse shaper based on four-tap finite impulse response. Due to different width designs in phase region of each tap, the phase differences for all taps are controlled by an external thermal source, resulting in an optical pulse shaper. We further demonstrate optical arbitrary waveform generation based on the optical pulse shaper assisted by an optical frequency comb injection. Four different optical waveforms are generated when setting the central wavelengths at 1533.78 nm and 1547.1 nm and setting the thermal source temperatures at 23℃ and 33℃, respectively. Our scheme has distinct advantages of compactness, capability for integrating with electronics since the integrated silicon waveguide is employed.     

Structural properties of a-SiO_x:H films studied by an improved infrared-transmission analysis method

An improved method of fitting point-by-point is proposed to determine the absorption coefficient from infrared(IR)transmittance. With no necessity of empirical correction factors, the absorption coefficient can be accurately determined for the films with thin thicknesses. Based on this method, the structural properties of the hydrogenated amorphous silicon oxide materials(a-SiOx:H) are investigated. The oxygen-concentration-dependent variation of the Si–O–Si and the Si–H related modes in a-SiOx:H materials is discussed in detail.     

Estimation of pulsed laser-induced single event transient in a partially depleted silicon-on-insulator 0.18-μm MOSFET

In this paper, we investigate the single event transient(SET) occurring in partially depleted silicon-on-insulator(PDSOI) metal–oxide–semiconductor(MOS) devices irradiated by pulsed laser beams. Transient signal characteristics of a 0.18-μm single MOS device, such as SET pulse width, pulse maximum, and collected charge, are measured and analyzed at wafer level. We analyze in detail the influences of supply voltage and pulse energy on the SET characteristics of the device under test(DUT). The dependences of SET characteristics on drain-induced barrier lowering(DIBL) and the parasitic bipolar junction transistor(PBJT) are also discussed. These results provide a guide for radiation-hardened deep sub-micrometer PDSOI technology for space electronics applications.     

Fabrication of pillar-array superhydrophobic silicon surface and thermodynamic analysis on the wetting state transition

Textured silicon （Si） substrates decorated with regular microscale square pillar arrays of nearly the same side length, height, but different intervals are fabricated by inductively coupled plasma, and then silanized by self-assembly octadecyl- trichlorosilane （OTS） film. The systematic water contact angle （CA） measurements and micro/nanoscale hierarchical rough structure models are used to analyze the wetting behaviors of original and silanized textured Si substrates each as a function of pillar interval-to-width ratio. On the original textured Si substrate with hydrophilic pillars, the water droplet possesses a larger apparent CAs （〉 90~） and contact angle hysteresis （CAH）, induced by the hierarchical roughness of microscale pil- lar arrays and nanoscale pit-like roughness. However, the silanized textured substrate shows superhydrophobicity induced by the low free energy OTS overcoat and the hierarchical roughness of microscale pillar arrays, and nanoscale island-like roughness. The largest apparent CA on the superhydrophobic surface is 169.8~. In addition, the wetting transition of a gently deposited water droplet is observed on the original textured substrate with pillar interval-to-width ratio increasing. Furthermore, the wetting state transition is analyzed by thermodynamic approach with the consideration of the CAH effect. The results indicate that the wetting state changed from a Cassie state to a pseudo-Wenzel during the transition.     

Large energy-loss straggling of swift heavy ions in ultra-thin active silicon layers

Monte Carlo simulations reveal considerable straggling of energy loss by the same ions with the same energy in fully-depleted silicon-on-insulator (FDSOI) devices with ultra-thin sensitive silicon layers down to 2.5 nm. The absolute straggling of deposited energy decreases with decreasing thickness of the active silicon layer. While the relative straggling increases gradually with decreasing thickness of silicon films and exhibits a sharp rise as the thickness of the silicon film descends below a threshold value of 50 nm, with the dispersion of deposited energy ascending above ±10%. Ion species and energy dependence of the energy-loss straggling are also investigated. For a given beam, the dispersion of deposited energy results in large uncertainty on the actual linear energy transfer (LET) of incident ions, and thus single event effect (SEE) responses, which pose great challenges for traditional error rate prediction methods.     

Photoelectric characteristics of silicon P–N junction with nanopillar texture:Analysis of X-ray photoelectron spectroscopy

Silicon nanopillars are fabricated by inductively coupled plasma(ICP) dry etching with the cesium chloride(CsCl)islands as masks originally from self-assembly. Wafers with nanopillar texture or planar surface are subjected to phosphorus(P) diffusion by liquid dopant source(POCl3) at 870℃ to form P–N junctions with a depth of 300 nm. The X-ray photoelectron spectroscopy(XPS) is used to measure the Si 2p core levels of P–N junction wafer with nanopillar texture and planar surface. With a visible light excitation, the P–N junction produces a new electric potential for photoelectric characteristic, which causes the Si 2p core level to have a energy shift compared with the spectrum without the visible light.The energy shift of the Si 2p core level is-0.27 eV for the planar P–N junction and-0.18 eV for the nanopillar one. The difference in Si 2p energy shift is due to more space lattice defects and chemical bond breaks for nanopillar compared with the planar one.     

Improved interface properties of an Hf02 gate dielectric GaAs MOS device by using SiNx as an interfacial passivation layer

A GaAs metal-oxide-semiconductor （MOS） capacitor with HfO2 as gate dielectric and silicon nitride （SiNx） as the interlayer （IL） is fabricated. Experimental results show that the sample with the SiNx IL has an improved capacitance- voltage characteristic, lower leakage current density （0.785 × 10^-6 Alcm^2 at Vfo ＋ 1 V） and lower interface-state density （2.9 × 10^12 eV^-1 ·cm^-2） compared with other samples with N2- or NH3-plasma pretreatment. The influences of post- deposition annealing temperature on electrical properties are also investigated for the samples with SiNx IL. The sample annealed at 600 ℃ exhibits better electrical properties than that annealed at 500 ℃, which is attributed to the suppression of native oxides, as confirmed by XPS analyses.     

Microstructure and blue photoluminescence enhancement of silicon nanoporous pillar array embedded in ferroelectric barium strontium titanate

A silicon nanoporous pillar array (Si-NPA) with micrometer/nanometer hierarchical structure was fabricated by hydrothermal etching, followed by spin-coating barium strontium titanate (BST) on Si-NPA substrate. The photoluminescence (PL) spectra of the Si-NPA and BST/Si-NPA thin film were investigated. The emission band of freshly prepared Si-NPA located at 630 nm, and a blueshift at 425 nm as well as degradation in intensity after annealing at 600 °C for 1 h was observed, which might be explained by a quantum confinement effect model. BST ferroelectric material provided a static-electric field and induced the excited carriers in Si-NPA to migrate toward the opposite direction and recombine in an interfacial oxide layer. Therefore, BST enhanced blue emission of Si-NPA as well as passivated Si-NPA.     

Hybrid device for acoustic noise reduction and energy harvesting based on a silicon micro-perforated panel structure

A kind of hybrid device for acoustic noise reduction and vibration energy harvesting based on the silicon micro- perforated panel （MPP） resonant structure is investigated in the article. The critical parts of the device include MPP and energy harvesting membranes. They are all fabricated by means of silicon micro-electro-mechanical systems （MEMS） tech- nology. The silicon MPP has dense and accurate micro-holes. This noise reduction structure has the advantages of wide band and higher absorption coefficients. The vibration energy harvesting part is formed by square piezoelectric membranes arranged in rows. ZnO material is used as it has a good compatibility with the fabrication process. The MPP, piezo- electric membranes, and metal bracket are assembled into a hybrid device with multifunctions. The device exhibits good performances of acoustic noise absorption and acoustic-electric conversion. Its maximum open circuit voltage achieves 69.41 mV.     

First-Principles Calculations of Atomic and Electronic Properties of T1 and In on Si（111）

The atomic and electronic structures of T1 and In on Si（111） surfaces are investigated using the firstprinciples total energy calculations. Total energy optimizations show that the energetically favored structure is 1/3 ML T1 adsorbed at the T4 sites on Si（111） surfaces. The adsorption energy difference of one T1 adatom between （√3 × √3） and （1 × 1） is less than that of each In adatom. The DOS indicates that TI 6p and Si 3p electrons play a very important role in the formation of the surface states. It is concluded that the bonding of TI adatoms on Si（111） surfaces is mainly polar covalent, which is weaker than that of In on Si（111）. So T1 atom is more easy to be migrated than In atom in the same external electric field and the structures of T1 on Si（111） is prone to switch between （√3 × √3） and （1 × 1）.     

Quantum confinement and surface chemistry of 0.8–1.6 nm hydrosilylated silicon nanocrystals

In the framework of density functional theory(DFT), we have studied the electronic properties of alkene/alkynehydrosilylated silicon nanocrystals(Si NCs) in the size range from 0.8 nm to 1.6 nm. Among the alkenes with all kinds of functional groups considered in this work, only those containing –NH2and –C4H3S lead to significant hydrosilylationinduced changes in the gap between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of an Si NC at the ground state. The quantum confinement effect is dominant for all of the alkenehydrosilylated Si NCs at the ground state. At the excited state, the prevailing effect of surface chemistry only occurs at the smallest(0.8 nm) Si NCs hydrosilylated with alkenes containing –NH2and –C4H3S. Although the alkyne hydrosilylation gives rise to a more significant surface chemistry effect than alkene hydrosilylation, the quantum confinement effect remains dominant for alkyne-hydrosilylated Si NCs at the ground state. However, at the excited state, the effect of surface chemistry induced by the hydrosilylation with conjugated alkynes is strong enough to prevail over that of quantum confinement.     

Reduction of the phosphorus contamination for plasma deposition of p-i-n microcrystalline silicon solar cells in a single chamber

This paper investigates several pretreatment techniques used to reduce the phosphorus contamination between solar cells. They include hydrogen plasma pretreatment, deposition of a p-type doped layer, i-a-Si:H or μc-Si:H covering layer between solar cells. Their effectiveness for the pretreatment is evaluated by means of phosphorus concentration in films, the dark conductivity of p-layer properties and cell performance.     

Characteristics of dual-frequency capacitively coupled SF_6/O_2 plasma and plasma texturing of multi-crystalline silicon

Due to it being environmentally friendly, much attention has been paid to the dry plasma texturing technique serving as an alternative candidate for multicrystalline silicon(mc-Si) surface texturing. In this paper, capacitively coupled plasma(CCP) driven by a dual frequency(DF) of 40.68 MHz and 13.56 MHz is first used for plasma texturing of mc-Si with SF6/O2gas mixture. Using a hairpin resonant probe and optical emission techniques, DF-CCP characteristics and their influence on mc-silicon surface plasma texturing are investigated at different flow rate ratios, pressures, and radio-frequency(RF)input powers. Experimental results show that suitable plasma texturing of mc-silicon occurs only in a narrow range of plasma parameters, where electron density n9e must be larger than 6.3 × 10cm-3and the spectral intensity ratio of the F atom to that of the O atom([F]/[O]) in the plasma must be between 0.8 and 0.3. Out of this range, no cone-like structure is formed on the mc-silicon surface. In our experiments, the lowest reflectance of about 7.3% for mc-silicon surface texturing is obtained at an [F]/[O] of 0.5 and ne of 6.9 × 109cm-3.