a-SiNx/nc-Si/a-SiNx双势垒结构中的电荷隧穿和存储效应

在等离子体增强化学气相沉积系统中利用大氢稀释逐层淀积技术制备nc-Si量子点阵列,用硅烷和氨气混合气体淀积氮化硅层,制备了a-SiN_x/nc-Si/a-SiN_x不对称双势垒结构,其中隧穿和控制a-SiN_x层的厚度分别为3和20 nm.利用电导-电压和电容-电压测量研究结构中的载流子隧穿和存储特性.在同一样品中观测到由于电荷隧穿引起的电导峰和由于电荷存储引起的电容回滞现象.研究结果表明,合理地选择隧穿层和控制栅层的厚度,就能够实现载流子发生共振隧穿进入到nc-Si量子点中,并被保存在nc-Si量子点中. 关键词： nc-Si量子点 电导峰 存储效应     

控制氧化层对双势垒纳米硅浮栅存储结构性能的影响

在等离子体增强化学气相沉积(PECVD)系统中,利用逐层淀积非晶硅(a-Si)和等离子体氧化相结合的方法制备二氧化硅(SiO₂)介质层.电容电压(C-V)和电导电压(G-V)测量结果表明：利用该方法在低温(250 ℃)条件下制备的SiO₂介质层均匀致密,其固定氧化物电荷和界面态密度分别为9×10¹¹cm^-2和2×10¹¹cm^-2·eV^-1,击穿场强达4.6 MV/cm,与热氧化形成的SiO₂介质层的性质相当.将该SiO₂介质层作为控制氧化层应用在双势垒纳米硅(nc-Si)浮栅存储结构中,通过调节控制氧化层的厚度,有效阻止栅电极与nc-Si之间的电荷交换,延长存储时间,使存储性能得到明显改善. 关键词： 等离子体氧化 二氧化硅 纳米硅 控制氧化层     

尺寸可控的纳米硅的生长模型和实验验证

基于经典热力学理论，对a-SiN_x/a-Si:H/a-SiN_x三明治结构或a-Si:H/a-SiN_x多层膜结构中纳米硅成核，以及从球形到鼓形的生长过程进行了研究. 建立了限制性晶化理论模型：在纳米硅生长过程中，由于界面能增大将导致生长停止，给出限制性晶化条件——a-Si:H子层厚度小于34 nm. 在激光晶化和常规热退火两种方法形成的a-SiN_x/nc-Si/a-SiN_x三明治结构和nc-Si/a-SiN_x多层膜结构中验证了该理论模型. 关键词： 非晶硅 纳米硅 激光辐照 结晶     

CHx掺杂SiCOH 低介电常数薄膜的物性热稳定性分析

研究了真空热处理对掺CH₄的SiCOH低介电常数薄膜的电流-电压(I-V)特性、电容-电压(C-V)特性、疏水性能以及微结构的影响. 结果表明：在热处理过程中,热稳定性较差的碳氢基团发生了热解吸,使薄膜的漏电流减小、绝缘性能改善,并使薄膜的导电行为更趋于空间电荷限流过程. 碳氢基团的热解吸使SiCOH/Si界面的界面态发生改变,导致SiCOH薄膜MIS结构的平带电压V_FB发生漂移. 封端的碳氢 关键词： SiCOH薄膜 热处理 结构与性能     

Nd0.67Sr0.33MnOy(y<3.0)中的自旋相关电致电阻效应

用固相反应法制备系列Nd_0.67Sr_0.33MnO_y(y = 3.00—2.80)多晶样品.样品输运性质表现出自旋相关电致电阻特征.对氧含量等于化学计量样品，在测量温度范围内电阻不随负载电流变化，I-V曲线符合线性欧姆定律.对氧含量低于化学计量样品，当高于某一特征温度时，电阻变化符合线性欧姆定律；但低于这一特征温度时，电阻大小与负载电流有关，I-V曲线偏离线 关键词： 钙钛矿结构锰氧化物 电致电阻效应 自旋相关界面输运 氧缺陷     

Al(OH)3溶胶浓度对TC4钛合金微弧氧化膜特性的影响

利用自制多功能微弧氧化(MAO)电源,在保持电学参数和处理时间不变的条件下对TC4钛合金表面进行了MAO处理,研究了Al(OH)₃溶胶浓度对钛合金MAO膜的生长特性、微观结构、相结构和电致变色特性的影响.结果表明:随着Al(OH)₃溶胶浓度(体积分数)C的增加,膜层的生长速率由慢到快逐渐增加,膜表面微孔尺寸和粗糙度逐渐增大,而微孔密度逐渐减小;当C≤10%时,膜层由锐钛矿相TiO₂组成,而当C>10%时,膜层中开始出现金红石相TiO₂并随着C的增加其相对含量逐渐增大,并在C=40%时,膜层全部由金红石相TiO₂组成;在pH＝2.0的HCl溶液中的循环伏安测试结果表明,C≤20%制备试样的膜层颜色变化不明显,随着C的进一步增加,制备试样的膜层颜色变化逐渐明显,并在C=40%时,其着色呈蓝色且色泽均匀;该试样在循环伏安测试过程中还表现出了良好的稳定性和可逆性. 关键词： 微弧氧化 氧化膜 微观结构 电致变色     

基于Al2O3/Pt纳米晶/HfO2叠层的MOS电容存储效应研究

采用电子束蒸发Pt和后快速热退火的方法,研究了退火条件对Pt纳米晶的生长特性的影响,结果显示Pt纳米晶的密度随退火温度的升高和退火时间的延长均表现出先增大后减小的趋势.在800℃下退火20 s能得到分布均匀的、密度为30×10¹¹ cm^-2的Pt纳米晶.进一步研究了基于Al₂O₃/Pt纳米晶/HfO₂叠层的MOS电容结构的存储效应,表明其在-3—+8 V扫描电压范围下C-V< 关键词： Pt纳米晶 快速热退火 原子层淀积 存储效应     

基于Si-rich SiNx/N-rich SiNy多层膜结构的量子点构筑及发光特性

利用等离子体增强化学气相沉积法制备Si-rich SiN_x/N-rich SiN_y多层膜,分别使用热退火和激光辐照技术对多层膜进行退火,以构筑三维限制、尺寸可控、有序的硅纳米晶.实验结果表明,经退火后,纳米硅晶粒在Si-rich SiN_x子层内形成,其尺寸可由Si-rich SiN_x子层厚度调控.实验还发现,激光辐照技术相比于热退火能更有效地改善多层膜的微结构,提高多层膜的晶化率,以激光技术诱导晶化的Si-rich SiN_x/N-rich SiN_y多层膜作为有源层构建电致发光器件,在室温下观察到了增强的电致可见发光,并且发光效率较退火前提高了40%以上. 关键词： 氮化硅 多层膜 限制结晶 纳米晶硅     

AlGaN/GaN异质结Ni/Au肖特基表面处理及退火研究

采用O₂等离子体及HF溶液对AlGaN/GaN异质结材料进行表面处理后，Ni/Au肖特基接触特性比未处理有了明显改善，反向泄漏电流减小3个数量级.对制备的肖特基接触进行200—600℃ 5min的N₂气氛退火，发现退火冷却后肖特基反向泄漏电流随退火温度增大进一步减小.N₂气中600℃退火后肖特基二极管C-V特性曲线在不同频率下一致性变好，这表明退火中Ni向材料表面扩散减小了表面陷阱密度；C-V特性曲线随退火温度增大向右移动，从二维电子气耗尽电压绝对值减小反映了肖特基势垒的提高. 关键词： AlGaN/GaN 肖特基接触 表面处理 退火     

电荷电压法测量DBD等离子体的放电参量

在DBD应用研究中，使用电荷电压法能够测量许多重要参量，如放电功率、放电间隙等效电容、电介质层等效电容、着火电压、放电间隙等效电压及放电间隙电场强度等．同时根据电荷电压图形随工作条件及状态变化的情况还可以诊断DBD等离子体的工作稳定性．文章对相关原理、模拟实验结果及实际应用效果进行了介绍．     

The charge storage of the nc—Si layer

Sandwiched structures (a-SiN_x/a-Si/a-SiN_x) have been fabricated by the plasma enhanced chemical vapour deposition technique. A Si nanocrystal (nc-Si) layer was formed by crystallization of an a-Si layer according to the constrained crystallization principle after quasi-static thermal annealing at 1100℃ for 30 min. Transmission electron microscopy (TEM) and Raman scattering spectroscopy clearly demonstrated that nc-Si grains were formed in the as-deposited a-Si layer after annealing. The density of nc-Si grains is about 10¹¹cm^-2 as shown by TEM photographs. Using capacitance－voltage (C－V) measurements we investigated the electrical characteristics of the sandwiched structures. The charge storage phenomenon of the nc-Si layer was observed from the shift of flat-band voltage (V_FB) in C－V curves at a high frequency (1 MHz). We estimated the density of nc-Si grains to be about 10¹¹cm^-2 from the shift value of V_FB, which is in agreement with the result of TEM photographs. At the same time, we found that the shift of V_FB increased with the increase of the applied constant dc voltage or the thickness of the nc-Si layer.     

The p recombination layer in tunnel junctions for micromorph tandem solar cells

A new tunnel recombination junction is fabricated for n–i–p type micromorph tandem solar cells. We insert a thin heavily doped hydrogenated amorphous silicon (a-Si:H) p + recombination layer between the n a-Si:H and the p hydrogenated nanocrystalline silicon (nc-Si:H) layers to improve the performance of the n–i–p tandem solar cells. The effects of the boron doping gas ratio and the deposition time of the p-a-Si:H recombination layer on the tunnel recombination junctions have been investigated. The current-voltage characteristic of the tunnel recombination junction shows a nearly ohmic characteristic, and the resistance of the tunnel recombination junction can be as low as 1.5 ·cm 2 by using the optimized p-a-Si:H recombination layer. We obtain tandem solar cells with open circuit voltage V oc = 1.4 V, which is nearly the sum of the V oc s of the two corresponding single cells, indicating no V oc losses at the tunnel recombination junction.     

Quantum emission efficiency of nanocrystalline and amorphous Si quantum dots

The paper presents the comparison of emission efficiencies for crystalline Si quantum dots (QDs) and amorphous Si nanoclusters (QDs) embedded in hydrogenated amorphous (a-Si:H) films grown by the hot wire-CVD method (HW-CVD) at the variation of technological parameters. The correlations between the intensities of different PL bands and the volumes of Si nanocrystals (nc-Si:H) and/or an amorphous (a-Si:H) phase have been revealed using X-ray diffraction (XRD) and photoluminescence (PL) methods. These correlations permit to discuss the PL mechanisms in a-Si:H films with embedded nc-Si QDs. The QD parameters of nc-Si:H and a-Si:H QDs have been estimated from PL results and have been compared (for nc-Si QDs) with the parameters obtained by the XRD method. Using PL and XRD results the relations between quantum emission efficiencies for crystalline (η_cr) and amorphous (η_am) QDs have been estimated and discussed for all studied QD samples. It is revealed that a-Si:H films prepared by HW-CVD with the variation of wire temperatures are characterized by better passivation of nonradiative recombination centers in comparison with the films prepared at the variation of substrate temperatures or oxygen flows.     

Structural and optical properties of Si/SiO2 multi-quantum wells

Structural and optical properties of Si/SiO₂ multi-quantum wells (MQW) were investigated by means of Raman scattering and photoluminescence (PL) spectroscopy. The MQW structures were fabricated on a quartz substrate by remote plasma enhanced chemical vapour deposition (RPECVD) of alternating amorphous Si and SiO₂ layers. After layer deposition the samples were subjected to heat treatments, i.e. rapid thermal annealing (RTA) and furnace annealing. Distinct PL signatures of confined carriers evidenced formation of Si-nanocrystals (nc-Si) in annealed samples. Analyses of Raman spectra also show presence of nc-Si phase along with amorphous-Si (a-Si) phase in the samples. The strong influence of the annealing parameters on the formation of nc-Si phase suggests broad possibilities in engineering MQW with various optical properties. Interestingly, conversion of the a-Si phase to the nc-Si phase saturates after certain time of furnace annealing. On the other hand, thinner Si layers showed a disproportionately lower crystalline volume fraction. From the obtained results we could assume that an interface strain prevents full crystallization of the Si layers and that the strain is larger for thinner Si layers. The anomalous dependence of nc-Si Raman scattering peak position on deposited layer thickness observed in our experiments also supports the above assumption.     

稳定、优质nc-Si/a-Si:H薄膜的研制和特性分析

利用等离子体增强化学气相沉积技术研制出了优质稳定的氢化非晶-纳米晶两相结构硅薄膜.薄膜的光电导率相对于器件质量的非晶硅有两个数量级的提高；光敏性也较好，光、暗电导比可以达到１０⁴，此外薄膜的光电导谱具有更宽的长波光谱响应.更为重要 的是薄膜的光致退化效应远小于典型的非晶硅薄膜，在光强为５０ｍW／ｃｍ²的卤钨灯光 照２４h后，光电导的衰退小于１０％.这种薄膜优良的光电性能源于薄膜中的非晶母体的存在使其在 光学跃迁中的动量选择定则发生松弛，因而具有大的光学吸收系数和 关键词： 非晶硅 微结构 光致变化     

Structure and transport mechanisms of Si/porous Si n-p junctions prepared by liquid phase epitaxy

Heterojunction devices of n-Si/p-PSi were fabricated by growing n-Si films onto p-type porous Si substrates by liquid phase epitaxy. The structure of the grown films was checked using scanning electron microscopy and X-ray diffraction spectroscopy. X-ray diffraction measurements showed that the grown films have monocrystalline structure oriented along (1 1 1) direction with mainly cubic phase. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured over the temperature range from 298 to 398 K. The analysis of the dark I-V characteristics of n-Si/p-PSi at several temperatures is done to elucidate the conduction mechanisms and the evaluation of the heterojunction parameters is presented. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage (V ≤ 0.4 V) the forward current is dominated by the recombination at the porous silicon side of the space charge region. In the 0.5 V ≤ V ≤ 1.4 V region, the current transport is due to the space charge—limited current mechanism dominated by a single trapping level of energy 0.41 eV. The reverse current is considered to be mainly generated in the depletion region of the porous silicon. The capacitance-voltage results confirm an abrupt junction with a homogenous distribution of the impurities inside the space charge region. Information on the depletion region, built-in voltage and net carrier concentration were obtained from the dark C-V characteristics.     

Boron-doped nanocrystalline silicon thin films for solar cells

This article reports on the structural, electronic, and optical properties of boron-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The films were deposited by plasma-enhanced chemical vapour deposition (PECVD) at a substrate temperature of 150 °C. Crystalline volume fraction and dark conductivity of the films were determined as a function of trimethylboron-to-silane flow ratio. Optical constants of doped and undoped nc-Si:H were obtained from transmission and reflection spectra. By employing p⁺ nc-Si:H as a window layer combined with a p′ a-SiC buffer layer, a-Si:H-based p-p′-i-n solar cells on ZnO:Al-coated glass substrates were fabricated. Device characteristics were obtained from current-voltage and spectral-response measurements.     

Subsurface localization of charge carriers in Si/SiO2/Si x Ge1 − x nanostructures

Analysis of the capacitance-voltage (C-V) characteristics reveals an elevated concentration of charge carriers under the surface of a silicon substrate due to the formation of elastically stressed regions induced in the substrate by Si _x Ge_{1 ? x} nanoislands grown on the preliminarily oxidized Si surface. The C-V characteristics exhibit charge density peaks at a depth from 700 to 1000 nm for Si/SiO₂/Si _x Ge_{1 ? x} structures with various thicknesses of the SiO₂ layer. The results of theoretical calculations of the electron density distribution in the bulk of the silicon substrate correspond on the whole to the C-V characteristics. The state of the interfaces in the structures with different thicknesses of the oxide layer, which determines the effects of surface and interfacial recombination as well as charge carrier scattering, is studied by analyzing the kinetics of decay of a photo-emf signal and the photo-emf distribution over the surface of the structure. The results can be used in the development of various devices based on SiGe with inclusions of oxide layers.