Micro-Raman光谱鉴定碳化硅单晶的多型结构

利用激光拉曼光谱仪测量了SiC单晶中不同多型的显微Raman光谱.在Raman光谱中,最大强度的FTA模和FTO模应出现在其简约波矢x等于该多型的六角度h处,据此对4H-SiC单晶中的多型进行了鉴定.同时采用高分辨X射线衍射测量了该晶片不同区域的摇摆曲线,将不同多型体的计算衍射角与实验值加以比较,对SiC晶片中的多型进行了标注,所得结论与激光Raman光谱测定结果相一致,说明Raman光谱是一种简单、快速地鉴定多型结构的强有力的工具.实验结果表明,在升华法生长4H-SiC单晶过程中,容易出现寄生6H、15R多型同4H多型的竞争生长,简单分析了寄生多型产生的原因.     

物理气相传输法生长碳化硅单晶原生表面形貌研究

晶体的生长原生面在一定程度上能反应出晶体生长机制和晶体缺陷分布的丰富信息。采用激光共聚焦显微镜偏光拼接技术和原子力显微镜对物理气相传输法生长的4H、6H-SiC单晶原生小面的表面形貌进行了观察和测试。偏光显微镜和原子力显微镜测试结果显示4H-SiC原生小面扩展后, 其周边趋向于形成六边形的生长台阶; 而6H-SiC原生小面扩展后, 其周边趋向于形成圆形的生长台阶。基于Jackson双层界面模型, 从热力学角度计算了4H、6H-SiC单晶的Jackson因子α分别为33.15和31.87, 故导致4H、6H-SiC单晶原生小面台阶形貌差异的是生长界面的粗糙程度和生长温度。原生面上的微管缺陷是生长台阶的起源, 借助原子力显微镜对多个微管进行了测试。由测试结果可知, 微管直径分布在760 nm-6.0 um之间, 相应的伯格斯矢量绝对值分布在5c~14c, 微管直径与伯格斯矢量平方值的商D/B²分布在11.1~23.6 nm^-1之间, 即通过原子力显微镜测试获得的微管结构数据不严格遵守Frank理论。     

同步辐射背反射白光形貌术观察6H-SiC单晶中的小角晶界和微管

利用同步辐射X射线形貌术对升华法生长的6H-SiC(0001)晶片中的小角晶界与微管缺陷进行了研究.小角晶界在同步辐射中的形貌成直线沿〈11- 00〉方向分布.根据螺位错附近的应变场和衍射几何,模拟了基本Burgers矢量大小的螺位错在同步辐射形貌像中的衍衬像,模拟结果与实验结果符合较好.据此指认了基本螺位错,并确定了微管Burgers矢量的大小.     

6H-SiC单晶表面ZnO薄膜的制备及其结构表征

利用脉冲激光淀积(PLD)技术在6H-SiC单晶衬底上制备了ZnO薄膜. 利用X射线衍射(XRD), 反射式高能电子衍射(RHEED)和同步辐射掠入射X射线衍射(SRGID)φ扫描等实验技术研究了ZnO薄膜的结构. 结果表明:在单晶6H-SiC衬底上制备的ZnO薄膜已经达到单晶水平, 不同入射角的SRGID结果, 显示了ZnO薄膜内部不同深度处a方向的晶格弛豫是不一致的, 从接近衬底界面处到薄膜的中间部分再到薄膜的表面处, a方向的晶格常数分别为0.3264、0.3272和0.3223nm. 通过计算得到ZnO薄膜的泊松比为0.504, ZnO薄膜与单晶6H-SiC衬底在平行于衬底表面a轴方向的实际晶格失配度为5.84%.     

拉曼面扫描表征氮掺杂6H-SiC晶体多型分布

采用物理气相传输法(Physical Vapor Transport, PVT)沿[0001]方向生长了一个直径为2英寸的氮掺杂6H-SiC晶体. 采用拉曼面扫描方法对晶体中多型的分布进行了细致表征, 研究了SiC晶体生长过程中多型的产生和演化. 在6H-SiC晶体中观察到了15R-SiC和4H-SiC两种多型. 在拉曼面扫描得到的晶体多型分布图上观察到了两类次多型结构区域, 一类是继承其生长界面上对应的次多型结构形成的次多型结构区; 另一类是由温度、压力等生长条件波动导致在6H-SiC主多型中出现的15R-SiC多型结构区. 第一类次多型结构区中掺入的氮元素较多, 载流子浓度较高, 并且随着晶体生长不断扩大; 第二类次多型结构区对晶体结晶质量的影响较小, 且提高生长温度可以抑制15R-SiC多型结构.     

Si(111)衬底上6H-SiC薄膜的低压化学气相外延生长与表征

在Si(111)衬底上,采用SiH4-C3H8-H2气体反应体系,通过低压化学气相沉积(LPCVD)工艺外延出结晶质量良好的SiC薄膜.低温光致发光谱表明该薄膜属于6H-SiC多型体.X射线衍射图表明该薄膜具有高度的择优取向性.扫描电子显微镜图表明该薄膜由片状SiC晶粒组成.拉曼光谱和透射电子衍射谱的结果进一步表明该薄膜具有较高的结晶质量.对Si(111)衬底上6H-SiC薄膜的生长机制进行了初步探讨.     

O.92PZN-0.08PT晶体的缺陷与畴结构研究

应用环境扫描电子显微术(ESEM)、原子力扫描显微术(AFM)、同步辐射白光形貌术(SRWBT)等形貌成像技术研究了0.92PZN-0.08PT晶体的表面缺陷形态与铁电畴结构.通过对畴结构动态演化的同步辐射形貌观察,可揭示出该晶体的结构相变过程.     

VLS同质外延6H-SiC薄膜生长的研究

碳化硅(SiC)是第三代宽禁带半导体材料,在高温、高频、高功率、光电子及抗辐射等方面具有巨大的应用潜力.以CH4、SiH4为反应气体,H2为载气,采用化学气相沉积法,利用气-液-固(VLS)生长机理,同质外延6H-SiC薄膜.结果表明,VLS机制能在外延薄膜的表面有效地封闭微管,但是由于n(C)/n(Si)较大,薄膜表面存在大量的台阶.为了进一步改善薄膜表面形貌,采用"两步法"工艺外延SiC薄膜,在封闭微管的同时提高了表面平整度,得到了质量较好的6H-SiC外延薄膜.     

MPCVD单晶体金刚石的生长实验进展

采用微波等离子体化学气相沉积（MPCVD）方法，在以往的实验条件上，改用CH4替代C2H5OH作为碳源，合成出单晶金刚石。使用宝石显微镜和环境扫描电子显微镜观察分析了MPCVD单晶金刚石膜的生长表面形貌。初步实验表明，在压力为12kPa，H2流量为300sccm，CH4流量为6sccm的生长环境中，可以合成出质量较好的...     

单分散棒状SnO2纳米单晶的制备及表征

以SnCl4·5H2O为主要原料,盐酸为抑制剂,采用压力-热晶法,在300～330℃成功地制备出单分散、高结晶度、结构稳定的氧化锡纳米棒,并用透射电子显微镜、X射线衍射等技术手段对氧化锡纳米单晶的结构和形貌进行表征.表征结果显示,制得的SnO2单晶具有棒状外观结构,其直径和长度分别为20～100nm、50～400nm.实验还考察了反应预压和盐酸浓度对产物结构和形貌的影响,实验结果表明,增加预压和适当的酸度都有利于四方晶型氧化锡单晶的形成.而且样品经900℃高温烧结,其形貌和尺寸基本不变.     

Identification and control of SiC polytypes in PVT method

Raman scattering spectra and transmission electron microscope are applied to 6H-SiC wafers. 15R-SiC polytype inclusion appears in 6H-SiC wafer. The proportion of 15R-SiC polytype inclusion decreases obviously by controlling temperature of growth surface and top powder via adjusting monitored temperature and relative position between the crucible and coils at certain interval in physical vapor transport method. When the temperature is below 2,100 °C, 15R-SiC polytype still exists in the 6H-SiC crystal; when the temperature is up to 2,100–2,300 °C and the relative position of crucible is suitable, there exists almost only 6H-SiC polytype in the whole wafer.     

Adsorption of Barium Atoms on Silicon Carbide

Technical Physics Letters - The adsorption of barium atoms on C and Si faces of 3C-, 6H-, and 4H-SiC polytypes is examined using the Haldane–Anderson model. The charge transfer from a barium...     

Investigation of the structure of (p)3C-SiC-(n)6H-SiC heterojunctions

The structure of (p)3C-SiC-(n)6H-SiC epitaxial structures obtained by sublimation epitaxy in vacuum on 6H-SiC substrates was studied by methods of X-ray topography, X-ray diffraction, and transmission electron microscopy. The results showed high structure perfection in the epitaxial layers of both SiC polytypes with a sharp interface between the 3C-SiC and 6H-SiC layers.     

Ge掺杂碳化硅晶体的生长缺陷

采用物理气相传输法(PVT)制备了2英寸Ge掺杂和非掺SiC晶体, 并使用二次离子质谱仪(SIMS)、显微拉曼光谱(Raman spectra)仪、体式显微镜、激光共聚焦显微镜(LEXT)和高分辨X射线衍射(HRXRD)仪等测试手段对其进行了表征。结果表明, Ge元素可以有效地掺入SiC晶体材料中, 且掺杂浓度达到2.52×10¹⁸/cm³, 伴随生长过程中Ge组份的消耗和泄漏, 掺杂浓度逐渐降低; 生长初期高浓度Ge掺杂会促使6H-SiC向15R-SiC晶型转化, 并随着生长过程中Ge浓度的降低快速地转回6H-SiC稳定生长。用LEXT显微镜观察发现, 生长初期过高的Ge掺杂导致空洞明显增多, 位错密度增加, 掺杂晶体中位错密度较非掺晶体增大一倍。HRXRD分析表明掺Ge能增大SiC晶格常数, 这将有利于提高与外延III族氮化物材料适配度, 并改善器件的性能。     

Synthesis and structural characterization of a heterocomposition based on porous layers of SiC polytypes

We have studied the structure of transverse cross sections of a heterocomposition consisting of porous layers of silicon carbide polytypes (substrate 6H-SiC/por-6H-SiC/epi-3C-SiC/por-3C-SiC). The epitaxial layer of 3C-SiC polytype (epi-3C-SiC) was grown by sublimation in vacuum on the surface of a porous 6H-SiC sublayer (por-6H-SiC) obtained by electrochemical etching of a 6H-SiC substrate. The boundary between the 3C-SiC epilayer and the porous 6H-SiC sublayer contains no defective transition layer, and the 3C-SiC epilayer is free of dislocations.     

Raman scattering as a probing method of subsurface damage in SiC

The subsurface damage extension has been investigated in 4H- and 6H-SiC as a function of the size of the polishing abrasive powder. Raman scattering spectra have been collected in the transverse ki//ksc configuration and, from an analysis of the high-frequency longitudinal phonon–plasmon coupled mode, the free carrier density has been evaluated at different distances beneath the sample surface. It was found that the variation of the carrier density depends strongly on the size of the polishing slurry. Moreover, comparing 6H- and 4H-SiC it was found that, for a given slurry 4H-SiC damaged is deeper than 6H-SiC.     

The quantitative calculation of SiC polytypes from measurements of X-ray diffraction peak intensities

An experimental determination on powder mixtures of SiC-3C and 6H polytypes using an X-ray goniometer system showed the possibility of quantitative determination of polytype fraction directly from peak intensities. In combination with calculated X-ray intensities of 15R and 4H polytype, the method yields a simple equation system for the relative quantities of SiC polytypes 15R, 6H, 4H and 3C in polycrystalline samples and powder mixtures.     

MBE-growth of heteropolytypic low-dimensional structures of SiC

The controlled growth of SiC heteropolytypic structures consisting of hexagonal (-) and cubic (3C-) polytypes has been performed by solid-source molecular beam epitaxy. On on-axis substrates, 4H/3C/4H-SiC(0001) and 6H/3C/6H-SiC(0001) structures were obtained by first growing some nanometers thick 3C-SiC layer at lower temperatures (1550 K) and Si-rich conditions, and subsequent growth of -SiC on top of the 3C-SiC layer at higher temperatures (1600 K) under more C-rich conditions. On off-axis substrates, multi-heterostructures consisting of 4H/3C- or 6H/3C-stacking sequences were also obtained by first nucleating selectively wire-like 3C-SiC nuclei on the terraces of well-prepared off-axis -SiC(0001) substrates at low T (<1500 K). Next, SiC was grown further in a step-flow growth mode at higher T and Si-rich condition. After the growth many wire-like regions consisting of 3C-SiC were found within the hexagonal SiC layer material matrix indicating a simultaneous step-flow growth of both the cubic and the hexagonal SiC material.