退火时间对SiC热解法制备石墨烯薄膜的影响

利用水平热壁式CVD外延炉开展了SiC热分解法制备石墨烯薄膜的实验,主要研究了不同的真空热处理时间对石墨烯薄膜生长的影响。SiC衬底的氢气在线刻蚀处理和热分解在同一炉次进行,高温时反应室释放出之前吸附的氢气不能有效地被分子泵抽除,SiC衬底的有效碳化时间有限,实验发现热处理时间超过30min之后,石墨烯层数并无明显变化。进一步加长热处理时间,石墨烯样品中出现局部氢插入层。     

高频石墨烯场效应晶体管研制

<正>石墨烯具有高电子迁移率和高热导率等优良特性,在毫米波、亚毫米波乃至太赫兹器件、超级计算机等方面具有广阔应用前景。然而石墨烯是二维结构,受衬底、栅界面的影响较体材料更为敏感,因而高性能的石墨烯FET器件的研制也成为一个极具挑战性的课题。南京电子器件研究所通过氢插入等工艺用SiC热解法制备出高质量的石墨烯薄膜,材枓霍尔迁移率达2000 cm2/(V·s)。在此基础上,开发了可降低栅介质散射作用的A1自氧化缓冲工艺,同时以自对准和T栅(150 nm栅脚,400 nm栅帽)减小器件的寄生效应,研制出了高性能石墨烯场效应     

Si面6H-SiC衬底外延石墨烯的异常硝酸掺杂效应

比较研究了Si面、C面SiC外延石墨烯以及CVD石墨烯的硝酸掺杂效应。结果表明对C面SiC外延石墨烯和CVD石墨烯,硝酸掺杂显现出p型掺杂特性使其方阻降低,这是由于硝酸与石墨烯氧化还原反应过程中电荷转移所导致;而对于Si面SiC外延石墨烯,硝酸掺杂则显现出n型掺杂特性使其方阻增大,这种异常掺杂效应是由于硝酸与石墨烯发生氧化还原反应释放出的热量使悬挂键吸附的氧脱附,增强了石墨烯与衬底之间的耦合效应,从而使得电子浓度增大,电子的迁移率显著减小。     

Si基GaN薄膜的制备方法及结构表征

分别采用射频磁控溅射、热壁化学气相沉积(CVD)、电泳沉积法制备GaN薄膜。利用扫描电镜(SEM)、荧光光谱仪对样品进行结构、形貌和发光特性的分析比较。射频磁控溅射方法中,把SiC中间层沉淀到Si衬底上,目的是为了缓冲由GaN外延层和Si衬底的晶格失配造成的应力。结果证实了SiC中间层提高了GaN薄膜的质量。热壁化学气相沉积法制备GaN晶体膜时,选择H2作反应气体兼载体,有利于GaN膜的形成。电泳沉积法显示所得样品为六方纤锌矿结构的GaN多晶薄膜。结果表明:溅射法制备的GaN薄膜结晶效果好;CVD法制备时GaN薄膜应用范围广;电泳沉积法操作方便、简单易行。     

银掺杂对MoS_2薄膜特性的影响

二硫化钼(MoS2)是一种具有类似石墨烯结构和性能的新型二维层状化合物,近年来因其独特的物理化学特性而成为研究热点。采用化学气相沉积法(CVD),以掺杂银的MoS2饱和溶液为原料,氩气为输运气体,在p-Si衬底上制备MoS2薄膜,并研究了银掺杂对MoS2薄膜的表面形貌、晶体结构、光吸收特性以及电学特性的影响。研究发现,银掺杂并未改变MoS2薄膜的晶体结构,而使MoS2薄膜的结晶度更好;银掺杂的MoS2薄膜反射率降低,光吸收增强,进而可以提高器件的光电转换效率。另外,银掺杂的MoS2薄膜表面更均匀平整,同时具有更良好的电学特性,其电子迁移率高达1.154×104 cm2·V-1·s-1,可用于制造一些晶体管和集成电路等半导体器件。     

籽晶偏向对高纯半绝缘4H-SiC晶体影响的研究

采用PVT法得到高纯4H-SiC体单晶。研究了0°、1°、4°晶体对晶体台阶流、晶体结晶质量、晶体缺陷、晶体电学性能的影响;晶体台阶流采用奥林巴斯显微镜进行表征,晶体缺陷采用莱卡体系显微镜进行表征,晶体结晶质量采用高分辨XRD进行表征,晶体电学性能采用非接触电阻率测试仪进行表征。实验结果表明:4°籽晶生长的晶体缺陷最少,1°与4°籽晶生长的晶体结晶质量相当,0°籽晶生长的晶体电学性能最均匀。     

在SixGe1-xC0.02衬底上直接生长石墨烯

基于锗衬底在石墨烯生长方面的自限制生长和表面催化特性,以甲烷(CH4)和氢气(H2)为前驱体,采用化学气相沉积(CVD)法分别在锗硅碳(SixGe1-xC0.02)(x=0.15,0.25,0.73)衬底和外延锗上直接生长石墨烯.研究了不同Si组分、H2与CH4体积流量比和生长温度对石墨烯质量的影响.利用光学显微镜(OM)、扫描电子显微镜(SEM)以及喇曼光谱对衬底和生长的石墨烯进行了表征分析.喇曼光谱结果表明,Si0.5Ge0.85C0.02衬底在750℃下可以生长出石墨烯,调节气体H2与CH4的体积流量比为50∶0.5时,生长出的石墨烯是双层的.OM和SEM结果表明,锗硅碳衬底具有比锗更好的热稳定性,高温下不会升华.     

偏晶向(0001)Si-面衬底上4H-SiC的LPCVD外延生长

化学气相沉积(CVD)是微电子器件用SiC外延材料的主要生长技术.为了获得高质量的4H-SiC外延材料,在偏向<1120>方向8°的4H-SiC(0001)Si-面衬底上,利用台阶控制生长技术进行4H-SiC的同质外延生长.表面形貌是SiC外延材料质量好坏的一个重要参数,为此研究了表面形貌与工艺参数的关系,探讨了4H-SiC外延膜的表面缺陷形成原因.利用Raman散射技术研究了非均匀4H-SiC外延材料的多晶型现象.     

偏晶向(0001)Si-面衬底上4H-SiC的LPCVD外延生长

化学气相沉积(CVD)是微电子器件用SiC外延材料的主要生长技术.为了获得高质量的4H-SiC外延材料,在偏向<1120>方向8°的4H-SiC(0001)Si-面衬底上,利用台阶控制生长技术进行4H-SiC的同质外延生长.表面形貌是SiC外延材料质量好坏的一个重要参数,为此研究了表面形貌与工艺参数的关系,探讨了4H-SiC外延膜的表面缺陷形成原因.利用Raman散射技术研究了非均匀4H-SiC外延材料的多晶型现象.     

偏晶向(0001)Si-面衬底上4H-SiC的LPCVD外延生长

化学气相沉积（CVD）是微电子器件用SiC外延材料的主要生长技术. 为了获得高质量的4H-SiC外延材料，在偏向〈1120〉方向8. 的4H-SiC (0001) Si-面衬底上，利用台阶控制生长技术进行4H-SiC的同质外延生长. 表面形貌是SiC外延材料质量好坏的一个重要参数，为此研究了表面形貌与工艺参数的关系，探讨了4H-SiC外延膜的表面缺陷形成原因. 利用Raman散射技术研究了非均匀4H-SiC外延材料的多晶型现象.     

Metal‐Free Growth of Nanographene on Silicon Oxides for Transparent Conducting Applications

Conventional methods to prepare large‐area graphene for transparent conducting electrodes involve the wet etching of the metal catalyst and the transfer of the graphene film, which can degrade the film through the creation of wrinkles, cracks, or tears. The resulting films may also be obscured by residual metal impurities and polymer contaminants. Here, it is shown that direct growth of large‐area flat nanographene films on silica can be achieved at low temperature (400 °C) by chemical vapor deposition without the use of metal catalysts. Raman spectroscopy and TEM confirm the formation of a hexagonal atomic network of sp²‐bonded carbon with a domain size of about 3–5 nm. Further spectroscopic analysis reveals the formation of SiC between the nanographene and SiO₂, indicating that SiC acts as a catalyst. The optical transmittance of the graphene films is comparable with transferred CVD graphene grown on Cu foils. Despite the fact that the electrical conductivity is an order of magnitude lower than CVD graphene grown on metals, the sheet resistance remains 1–2 orders of magnitude better than well‐reduced graphene oxides.     

Temperature Dependence of Epitaxial Graphene Formation on SiC(0001)

The formation of epitaxial graphene on SiC(0001) surfaces is studied using atomic force microscopy, Auger electron spectroscopy, electron diffraction, Raman spectroscopy, and electrical measurements. Starting from hydrogen-annealed surfaces, graphene formation by vacuum annealing is observed to begin at about 1150°C, with the overall step-terrace arrangement of the surface being preserved but with significant roughness (pit formation) on the terraces. At higher temperatures near 1250°C, the step morphology changes, with the terraces becoming more compact. At 1350°C and above, the surface morphology changes into relatively large flat terraces separated by step bunches. Features believed to arise from grain boundaries in the graphene are resolved on the terraces, as are fainter features attributed to atoms at the buried graphene/SiC interface.     

二硫化钼-石墨烯垂直异质结的制备与表征

以采用化学气相沉积法(CVD)生长的单层石墨烯为导电电极、四硫代钼酸铵水溶液为电解质,通过电化学沉积法合成了二硫化钼/石墨烯(MoS2/graphene)垂直异质结。将合成的MoS2/graphene垂直异质结通过CVD在氢气(H2)和氩气(Ar)环境下进行退火处理。利用拉曼光谱、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)系统地分析了样品的物质成分、表面形貌和厚度等。这种简单、环保、低成本的制备大面积MoS2/graphene垂直异质结的方法具有普遍适用性,为其他垂直异质结的制备开辟了新途径。     

Growth of Large Crystalline Grains of Vanadyl‐Phthalocyanine without Epitaxy on Graphene

The performance of organic semiconductor thin films in electronic devices is related to their crystal structure and morphology, with charge transport mobility dependent on the degree of crystallinity and on the crystallographic orientation. Here organic molecular beam deposition of vanadyl phthalocyanine is studied on graphene and it is shown that crystalline grains up to several micrometers across can be formed at substrate temperatures of 155 °C, compared to room temperature grain sizes of ≈30 nm. Transmission electron microscopy confirms the presence of long range order at elevated substrate temperatures and reveals that the molecules are stacked in an edge‐on orientation, but are not epitaxially aligned to the graphene. The crystalline grain sizes are significantly larger on graphene than on disordered substrates such as graphene oxide and silicon oxide. The effect on charge transport is probed by conducting atomic force microscopy, with the high temperature films on graphene showing increased mobility and uniformity and decreased trap density. These results illustrate an important advantage for the integration of graphene electrodes with organic semiconductor devices: the homogeneous surface of graphene results in high diffusion and low nucleation rates for thin film growth, encouraging the formation of highly crystalline films even with nonepitaxial growth.     

Wetting‐Assisted Crack‐ and Wrinkle‐Free Transfer of Wafer‐Scale Graphene onto Arbitrary Substrates over a Wide Range of Surface Energies

The polymer‐supported wet transfer of chemical vapor deposition‐grown graphene provides high‐quality large‐area graphene on a target substrate. The transfer‐induced defects that result from these processes, such as micrometer‐scale folds and cracks, have been regarded as an inevitable problem. Here, the transfer processes are thoroughly examined stage‐by‐stage and it is found that lamination wrinkles, which cause defects in the graphene, are generated as a result of the high contact angles of the trapped transfer medium liquids. Systematic theoretical and experimental studies demonstrate that a liquid droplet with a low surface tension trapped between the polymer/graphene film and the substrate minimizes lamination wrinkles during the transfer process by completely wetting the target substrate, regardless of the surface energy. In connection with these results, a simple and broadly applicable transfer method is developed using an organic liquid with a low surface tension to uniformly transfer high‐quality graphene onto arbitrary substrates, even onto superhydrophobic substrate. The graphene obtained using the proposed organic liquid transfer method displays better electrical and mechanical properties than the graphene transferred by the conventional method using water. This effective and practical transfer method provides an approach to obtaining high‐quality graphene for use in graphene‐based devices.     

镍硅化物诱导横向晶化制备高性能多晶硅薄膜晶体管

提出一种新的采用镍硅化物作为种子诱导横向晶化制备低温多晶硅薄膜晶体管的方法。分别采用微区Raman、原子力显微镜和俄歇电子能谱对制备的多晶硅薄膜进行结构和性能表征,并以此多晶硅薄膜为有源层制备了薄膜晶体管,测试其I-V转移特性。测试结果显示,制备的多晶硅薄膜具有较低的金属污染和较大的晶粒尺寸,且制备的多晶硅薄膜晶体管具有良好的电学特性,可以有效地减小漏电流,同时可提高场效应载流子迁移率。这主要是由于多晶硅沟道区中镍含量的有效降低使得俘获态密度减少。     

低能Ar+刻蚀时间对抛光单晶LiNbO3薄膜忆阻器的影响

调节低能Ar+刻蚀对单晶LiNbO3(LN)的刻蚀时间,制备了不同LN厚度的单晶薄膜忆阻器。利用扫描电子显微镜(SEM)、原子力显微镜(AFM)和电子顺磁共振(EPR)对器件的微观形貌与表面氧空位进行了表征。通过电流-电压曲线(IV曲线)、数据保持特性(Retention)和抗疲劳特性(Endurance)的测试,探究了刻蚀时长对器件电学行为的影响。结果表明,随刻蚀时间增加,器件表面光滑均匀,氧空位浓度增加,电形成电压显著降低。同时,尽管LN薄膜厚度减小后,器件的开关比(On/Off)略有降低,但其具有更好的数据保持特性。该方法适用于对由离子注入剥离法制备的单晶薄膜进行改性,以调控其阻变特性,使之可在高密度存储、神经形态计算等领域得到应用。     

High-performance polythiophene thin-film transistors with nematic liquid crystal modification

The influence of nematic liquid crystal molecules on the electrical properties and microstructure of polymer semiconductors poly(3-hexylthiophene) (P3HT) was investigated. It was found that the introduction of nematic liquid crystal molecules can significantly improve the performance of P3HT thin-film transistors, providing better electrical characteristics and enhanced mobility. The field-effect mobility of the device with liquid crystal modification can be enhanced by up to a factor of ten with respect to that of the pure P3HT device. UV–visible absorption spectroscopy, X-ray diffraction, and atomic force microscopy measurements show that the enhancement of charge-carrier mobility is achieved through a more highly organized morphology and a reduction in the density of traps presents in the P3HT/liquid crystal structure. The results shown here therefore illustrate a high-performance solution-processable thin-film transistors, which is quite feasible and can pave a key step for the practical applications of organic electronic devices.     

CO2‐Laser‐Induced Growth of Epitaxial Graphene on 6H‐SiC(0001)

The thermal decomposition of SiC surface provides, perhaps, the most promising method for the epitaxial growth of graphene on a material useful in the electronics platform. Currently, efforts are focused on a reliable method for the growth of large‐area, low‐strain epitaxial graphene that is still lacking. Here, a novel method for the fast, single‐step epitaxial growth of large‐area homogeneous graphene film on the surface of SiC(0001) using an infrared CO₂ laser (10.6 μm) as the heating source is reported. Apart from enabling extreme heating and cooling rates, which can control the stacking order of epitaxial graphene, this method is cost‐effective in that it does not necessitate SiC pre‐treatment and/or high vacuum, it operates at low temperature and proceeds in the second time scale, thus providing a green solution to EG fabrication and a means to engineering graphene patterns on SiC by focused laser beams. Uniform, low–strain graphene film is demonstrated by scanning electron microscopy, X‐ray photoelectron spectroscopy, secondary ion‐mass spectroscopy, and Raman spectroscopy. Scalability to industrial level of the method described here appears to be realistic, in view of the high rate of CO₂‐laser‐induced graphene growth and the lack of strict sample–environment conditions.