Efficiency enhancement in a-plane InGaN/GaN light emitters with carbon nanotubes

This study investigates the coupling modes of a-plane InGaN/GaN mutiquantum wells (MQWs) with single-walled carbon nanotubes (SWCNTs). The enhancement of light emissions at resonance photon energies can be explained by the surface plasmon coupling of the MQW-SWCNT hybrid structure. The photoluminescence (PL) enhancement ratios of the indigo (2.90 eV) emission from MQWs with SWCNTs reveal three coupling modes at 2.50 eV, 2.97 eV, and 3.42 eV. In addition, the trend of the PL intensity ratios and efficiencies corresponds to that of the PL enhancement ratios. The PL efficiencies for the green (2.46 eV) and indigo (2.90 eV) emissions of SWCNT-coated MQWs are 32% and 110% better than the corresponding values of uncoated MQWs, respectively. The results show that the MQW-SWCNT hybrid structure has the potential to be applied in high-efficiency light emitters in the visible and ultraviolet range.     

Comparative study of (Ba,Sr)TiO3 films prepared by electron cyclotron resonance plasma sputtering and metal-organic decomposition

(Ba,Sr)TiO₃ films were prepared on Pt/Ti/SiO₂/Si substrates by mirror-confinement-type electron cyclotron resonance (ECR) plasma sputtering as well as by metal-organic decomposition (MOD). The films prepared by ECR plasma sputtering were crystallized at lower temperatures with better crystallinity and a denser structure than those by MOD. As for dielectric constant, films prepared by ECR plasma sputtering exhibited a relatively high value over 500 at a low annealing temperature of 873 K, whereas films by MOD exhibited approximately 350. This is attributed to the better crystallinity and the denser structure of the films by ECR plasma sputtering. The leakage current density of the films was found to be similar in both processes.     

Scalable network electrical devices using ZnO nanowalls

We report the fabrication and electrical characteristics of scalable nanowall network devices and their gas sensor applications. For the network device fabrications, two-dimensional ZnO nanowall networks were grown on AlN/Si substrates with a patterned SiO(2) mask layer using selective-area metal-organic vapor-phase epitaxy. The ZnO nanowalls with c-axis orientation were heteroepitaxially grown on AlN/Si substrates, and were single-crystalline, as determined by x-ray diffraction and transmission electron microscopy. The electrical conductivity of the nanowall networks was measured as a function of nanowall dimensions. The conductance increased linearly with the channel width for widths larger than 1 μm, but saturated at 36 μS for widths below 1 μm. This conductance scaling behavior is explained by enhanced conduction through the regions near the edge of the patterned growth areas, where the density of the networks was higher. Gas sensor applications were investigated using the nanowall network devices, and highly sensitive gas detection was demonstrated.     

Characterization of tantalum oxy-nitrides deposited by ECR sputtering

We have investigated the electrical characteristics of tantalum oxy-nitride (TaON) films deposited using electron cyclotron resonance (ECR) plasma sputtering. A pure tantalum metal target was used as raw material combined with gases of oxygen and nitrogen. The electrical properties have been measured using metal-insulator-metal (MIM) structures of Al/TaON/Ru/Si or metal-insulator-semiconductor (MIS) structure of Al/TaON/Si. By controlling the oxygen gas flow in a moderate low gas flow rate at fixed nitrogen gas flow, TaON films have been stably obtained with the refractive indices of over 2.5 at 632.8 nm wavelength, and the dielectric constants of over 30. However, the leakage currents have increased with an increase in the dielectric constants. To improve the leakage current, we have investigated the periodical deposition process, in which the ECR plasma irradiation was additionally introduced after thin TaON film was deposited. The breakdown strength of about 1 MV/cm was obtained by the measurement using MIM structure. By the estimation of the C-V characteristics of the silicon-MIS structure using TaON, the dielectric constant of 34 was obtained for a TaON thickness of 12 nm.     

Low cost fabrication of the large-area anti-reflection films from polymer by nanoimprint/hot-embossing technology

In this paper, we present a low cost approach to produce large-area polymer sheets with sub-wavelength nanostructures. The fabricated polymer films would have great potentials to attach to optical or solar-cell-related consumer products when anti-reflection/anti-glaring is mandatory. We employed a special electron cyclotron resonance (ECR) plasma process to fabricate the SWSs with large area directly on silicon substrates. Homogeneously distributed nanotips on the full 4 inch silicon substrate were fabricated by using gas mixtures of silane, methane, argon and hydrogen. An Ni-Co metal mold with a hardness of 550 HV was produced through the replication of the Si mold by electroplating. Afterwards, the molding process was applied to manufacture the nanostructures in PMMA plates in large volume. The nanostructures in PMMA plates with aspect ratios of 4 and diameters of 150?nm were fabricated. The fabricated PMMA sheets could generate the gradient of the refractive indices, absorb the light and greatly reduce the reflectivity. Compared with the PMMA without SWSs, the reflectivity of PMMA with SWSs decreased dramatically from 4.25% to 0.5% at the wavelength of light from 400 to 800?nm.     

A comparison of nitrous oxide and hydrogen ECR plasma discharges for silicon solar cell passivation

The passivation of crystalline Si solar cells using nitrous oxide (N₂O) electron cyclotron resonance (ECR) plasma discharges has been studied and compared with ECR hydrogen passivation. The cells consisted of ECRCVD grown microcrystalline Si emitter layers on single crystal Si (sc-Si) and multicrystalline Si (mc-Si) substrates, without anti-reflective coatings or surface texturing. For cells on sc-Si substrates, hydrogen passivation is more effective at a substrate temperature of 300 °C and low microwave power (300 W). With increased power (500 W) H₂ is less effective than N₂O due to hydrogen plasma damage leading to a significant fall in the cell fill factor. In comparison with H₂, N₂O discharges lead to a significantly better (by > a factor of 2) improvement in the performance of cells on mc-Si substrates for treatment times of ≤15 min at a passivation temperature of 300 °C and 300 W microwave power. XPS measurements suggest that a surface oxide layer containing N and C atoms is formed by the N₂O plasma which, most likely, reduces the surface state density and, hence, carrier recombination.     

A comparison of nitrous oxide and hydrogen ECR plasma discharges for silicon solar cell passivation

The passivation of crystalline Si solar cells using nitrous oxide (N₂O) electron cyclotron resonance (ECR) plasma discharges has been studied and compared with ECR hydrogen passivation. The cells consisted of ECRCVD grown microcrystalline Si emitter layers on single crystal Si (sc-Si) and multicrystalline Si (mc-Si) substrates, without anti-reflective coatings or surface texturing. For cells on sc-Si substrates, hydrogen passivation is more effective at a substrate temperature of 300 °C and low microwave power (300 W). With increased power (500 W) H₂ is less effective than N₂O due to hydrogen plasma damage leading to a significant fall in the cell fill factor. In comparison with H₂, N₂O discharges lead to a significantly better (by > a factor of 2) improvement in the performance of cells on mc-Si substrates for treatment times of ≤15 min at a passivation temperature of 300 °C and 300 W microwave power. XPS measurements suggest that a surface oxide layer containing N and C atoms is formed by the N₂O plasma which, most likely, reduces the surface state density and, hence, carrier recombination.     

Estimate of the negative ion density in reactive gas plasmas

The negative ion density in a SF₆/Ar double plasma is estimated. Here, the density ratio of negative ions to positive ions is evaluated from the reduction rates of the ion and electron saturation current. Furthermore, the negative ion density obtained with this method is confirmed to agree with that calculated from the measured phase velocity of the ion acoustic wave (fast mode) when <0.6, where the positive and negative ion mass are obtained from the spectrum analysis with a quadruple mass spectrometer (QMS) system. The negative ion density in fluorocarbon ECR plasma is also estimated by means of the Langmuir probe method. It is found that in fluorocarbon ECR plasma is less than 0.5.     

等离子体源增强磁控溅射沉积Al2O3薄膜研究

采用电子回旋共振微波等离子体源增强磁控溅射沉积氧化铝薄膜.X射线光电子谱和X射线衍射分析表明,在600℃沉积温度下,Si（100）基片上获得了亚稳的具有化学计量配比成分、面心立方结构的γ-Al₂O₃薄膜.薄膜的折射率为1.7,与稳定的α-Al₂O₃体材料相当.     

Si3N4薄膜的表面微观特性

利用偏心静电单探针诊断了反应室内的等离子体密度的空间分布;在不同的工艺条件下制备了Si3N4薄膜,由STM和Telystep-Hobbso轮廓仪研究了ECR－PECVD制备的Si3N4薄膜的表面微观特性,分析了沉积温度对ECR－PECVD制备的Si3N4薄膜表面平整度特性影响的物理机理;结果表明ECR－PECVD制备的薄膜是一种表面均匀致密的纳米Si3N4薄膜。     

微波ECR等离子体源离子注入法制备DLC薄膜

用微波ECR等离子体源离子注入 (PSII)法 ,在硅片 ( 10 0 )上制备了类金刚石 (DLC)薄膜 ,工作气体采用CH4气体 ,研究了不同的气体流量对薄膜的影响。对制备的DLC薄膜 ,用拉曼光谱、FT IR光谱、AFM以及纳米压痕等手段对化学成分、化学键结构、表面形貌以及硬度等进行了表征     

厚度对DLC薄膜内应力的影响研究

采用ECR微波等离子体增强化学气相沉积的方法于C1H2/H2/Ar2等离子环境中在单晶Si(111)晶面上制备了不同厚度的DLC膜样品,研究了薄膜的厚度随沉积时间的变化及薄膜的硬度、内应力随厚度的变化关系.结果表明,在沉积时间变化范围内,厚度与沉积时间基本呈线性关系,沉积速率可达80nm/min;制备态样品存在的内应力...     

微波电子回旋共振等离子体的阻抗特性分析

基于微波电子回旋共振（ECR）等离子体中的物理和化学性质变化会引起微波传输线阻抗的变化，采用微波三探针研究了ECR等离子体的微波阻抗随装置运行参数的变化情况，并通过一个简单的放电等效电路将阻抗的变化和等离子体性质的变化联系起来。实验结果表明，通过对ECR等离子体进行阻抗特性分析，可以在不对其产生干扰的情况下了解其性质的变化。阻抗特性分析为ECR等离子体的机理研究提供了一种新的诊断途径，有利于ECR等离子体工艺的推广和应用。     

Bias-independent growth of carbon nanowalls by microwave electron-cyclotron resonance plasma CVD

The investigations reported here describe the synthesis of carbon nanowalls (CNWs) by microwave electron-cyclotron resonance (ECR) plasma-assisted chemical vapour deposition (PACVD) process without an application of external bias to the substrate during growth. CNWs were grown on silicon (Si) substrates using hydrogen (H₂)/methane (CH₄) plasma at 650°C substrate temperature. Nickel (Ni) was used as a catalyst for the synthesis of CNWs. To the best of our knowledge, this is the first report that describes the bias-independent growth of CNWs using the ECR PACVD process. Formation of CNWs is confirmed by scanning electron microscopy and Raman spectroscopy. The discussion part also includes a possible growth mechanism for CNWs in terms of the role of surface plasmons.     

Ultraviolet photodetectors with MgZnO nanowall networks grown by molecular beam epitaxy on Si(1 1 1) substrates

Mg_0.05Zn_0.95O nanowall networks ultraviolet (UV) photodetector was fabricated on Si(1 1 1) by plasma-assisted molecular beam epitaxy. Based on the Mg_0.05Zn_0.95O nanowall networks, planar geometry photoconductive type metal-semiconductor-metal photodetector was fabricated. At 5 V bias, the peak responsivity of 24.65 A/W was achieved at 352 nm, corresponding to an external quantum efficiency of ∼8490%. Such high external quantum efficiency was attributed to the photoconductive gain, which can be explained by the presence of oxygen-related hole-trap states at the nanowall surface. The response time of 25 ms was determined by the measurements of photocurrent versus modulation frequency.     

Piezoelectric field in highly stressed GaN-based LED on Si (1 1 1) substrate

Stress states in GaN epilayers grown on Si (1 1 1) and c-plane sapphire, and their effects on built-in piezoelectric field induced by compressive stress in InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) were investigated using the electroreflectance (ER) spectroscopic technique. Relatively large tensile stress is observed in GaN epilayers grown on Si (1 1 1), while a small compressive stress appears in the film grown on c-plane sapphire. The InGaN/GaN MQWs of LED on c-plane sapphire substrate has a higher piezoelectric field than the MQWs of LEDs on Si (1 1 1) substrate by about 1.04 MV/cm. The large tensile stress due to lattice mismatch with Si (1 1 1) substrate is regarded as external stress. The external tensile stress from the Si substrate effectively compensates for the compressive stress developed in the active region of the InGaN/GaN MQWs, thus reducing the quantum-confined Stark effect (QCSE) by attenuating the piezoelectric polarization from the InGaN layer.     

电子回旋共振等离子体源的朗谬尔探针诊断

电子回旋共振(ECR)等离子体以其密度高、工作气压低、均匀性好、参数易于控制等优点在超大规模集成电路工艺中获得了广泛的应用.利用朗谬尔探针对ECR等离子体进行了初步的诊断研究,测量了等离子体的单探针伏安特性并计算出电子温度,电子密度和等离子体电势等参量.实验证明,ECR等离子体源能够稳定地产生电子温度较低的高密度等离子体.     

Structures and light emission properties of nanocrystalline FeSi2/Si formed by ion beam synthesis with a metal vapor vacuum arc ion source

Thin layers of nanocrystalline FeSi₂ embedded in Si structures have been formed by Fe implantation using a metal vapor vacuum arc (MEVVA) ion source under various implantation and thermal annealing conditions. The microstructures were studied in details and correlated with the photoluminescence (PL) properties. It is found that higher lattice coherence between the FeSi₂ nanocrystals and the Si matrix is associated with better light emission efficiency. Multiple-cycle implantation schemes were introduced and it is shown that with appropriate process design the dose quenching effect can be suppressed to achieve light emission enhancement in higher dose samples. De-convolution of the PL spectra into two or three peaks was performed and their temperature and excitation power dependence were analyzed. The analysis results indicate that the 1.55-μm emission really originated from FeSi₂ and that the emission peaks are likely donor- or accepted-level-related. MOS structures with the incorporation of implanted nanocrystalline FeSi₂ were fabricated. Electroluminescence (EL) spectra from these devices showed two peak features of which one peak corresponds to FeSi₂ emission and the other corresponds to enhanced Si band-edge emission. Clear room-temperature EL signals from these device structures were observed. A model is proposed to qualitatively understand the temperature dependence of the EL spectra.     

Coulomb interaction of electron gas in MQWs Si/Si1 − xGex/Si

We present a theoretical analysis of the conduction and valence-band diagrams of SiGe/Si Multiple Quantum Wells (MQWs), having a specific “W” geometry, and designed for emission or photodetection around the 1.55 μm wavelength. Peculiar features have been extrapolated by solving self-consistent Schrödinger and Poisson equations, taking into account the electrostatic attraction induced by carrier injection. As a result, Coulomb interaction strongly modifies the band profiles and increases the electron probability density at the quantum well interfaces; the injected carrier concentration enhances electron–hole wave functions overlap and the in-plane oscillator strength. These MQWs structures, strain-compensated on relaxed Si_0.75Ge_0.25 pseudo-substrates, are potentially interesting for telecom applications.     

新型微波ECR-PECVD装置的研制

介绍一台新型的ECR-PECVD装置.这一装置设计和采用了一种由单个电磁线圈和永磁体单元组合的新型磁场,使整个装置结构明显简化.为提高装置的微波转换效率,通过计算机仿真微波场在等离子体室的分布,选择和采用了一种新型的矩形耦合波导.应用这一装置分解H2稀释的SiH4气体以沉积a-Si:H薄膜,获得了2 nm/s以上的高沉积速率.