碳化硅中氦离子高温注入引入的缺陷及其退火行为的光谱研究

对氦（He）离子高温（600 K）注入6H-SiC中的辐照缺陷,在阶梯温度退火后演化行为的拉曼光谱和室温光致发光谱的特征进行了分析.这两种方法的实验结果表明,离子注入所产生晶格损伤的程度与注入剂量有关;高温退火导致损伤的恢复,不同注入剂量造成的晶格损伤需要不同的退火温度才可恢复.在阶梯温度退火下呈现出了点缺陷的复合、氦-空位团的产生、氦泡的形核、长大等特性.研究表明：高温（600 K）注入在一定剂量范围内是避免注入层非晶化的一个重要方法,为后续利用氦离子注入空腔掩埋层吸杂或者制备低成本、低缺陷密度的绝缘层 关键词： 6H-SiC 离子注入 拉曼光谱 光致发光谱     

n型6H-SiC拉曼散射光谱的温度特性（英文）

三片具有不同载流子浓度的n型6H-SiC体材料用于83K到673K的变温拉曼散射研究,能够得到变温的拉曼散射模。通过测量可以得到,随着温度的增长,不同的声子散射模的拉曼峰逐渐变小。运用声子频率的温度特性计算公式,对三片样品的三个声子模的峰位进行拟合能够得到很好的拟合结果。6H-SiC样品的纵光学声子模(LOPC)的拉曼位移像其他的拉曼模一样,随着温度的增加而变小。在较高的温度时所有的声子模明显展宽。     

Kr离子注入SiC的拉曼光谱研究

应用拉曼光谱研究了5 MeV Kr离子（注量分别为5×1013,2×1014,1×1015 ions/cm2）室温注入6H SiC单晶及其高温退火处理后结构的变化。 研究表明, 注入样品的拉曼光谱中不仅出现了Si—C振动的散射峰, 还产生了同核Si—Si键和C—C键散射峰。 Si—C散射峰强度随退火温度升高而增强, 当退火温度高达1000 ℃时, 已接近未辐照SiC的散射峰强度。晶体Si—Si键散射峰强度随退火温度变化不大, 而非晶Si—Si键散射峰强度随退火温度的增加逐渐消失。相对拉曼强度（Relative Raman Intensity, 简称RRI）随注量的增加逐渐减小并趋于饱和, 且不同退火温度样品的饱和注量不相同; RRI随退火温度的增加逐渐升高, 这在低注量样品中表现得尤为明显。 低、中、高3种注量样品的RRI随退火温度的增加从重合逐渐分离, 并且退火温度越高, 分离越大。 Raman spectroscopy was used to study the structure changes of 6H SiC single crystal implanted with 5 MeV Kr (Krypton) at room temperature and subsequently annealed at high temperature. The Raman spectrum of the implanted SiC displays not only Si—C bonds vibration peaks, but also homonuclear Si—Si and C—C bond vibration peaks. Si—C bond vibration peaks gradually strengthen with increasing temperature. When annealing at 1000 ℃, the peak intensity of Raman spectrum is close to that of virgin specimen. It is found that crystal Si—Si bond vibration peaks do not change when annealing, but amorphous Si—Si bond vibration peaks disappear with increasing annealing temperature. The Relative Raman Intensity (RRI) values decrease with increasing fluence and tend to saturate, but the saturation fluences is different for various anneal temperature. The RRI values increases with raising annealing temperature, which is more obvious in low implanted specimens. At the same time, the RRI values separate gradually with increasing temperature and this phenomenon is strengthened by annealing temperature.     

N型4H-SiC低温拉曼光谱特性

利用拉曼散射技术对N型4H-SiC单晶材料进行了30～300 K温度范围的光谱测量。实验结果表明,随着温度的升高,N型4H-SiC单晶材料的拉曼峰峰位向低波数方向移动,峰宽逐渐增宽。分析认为,晶格振动随着温度的升高而随之加剧,其振动恢复力会逐渐减小,使振动频率降低;原子相对运动会随温度的升高而加剧,使得原子之间及晶胞之间的相互作用减弱,致使声学模和光学模皆出现红移现象。随着温度的升高,峰宽逐渐增宽。这是由于随着温度的升高声子数逐渐增加,增加的声子进一步增加了散射概率,从而降低了声子的平均寿命,而声子的平均寿命与峰宽成反比,因此随着温度的升高峰宽逐渐增宽。声子模强度随温度升高呈现不同规律,E₂(LA),E₂(TA),E₁(TA)和A₁(LA)声子模随着温度升高强度单调增加,而E₂(TO),E₁(TO)和A₁(LO)声子模强度出现了先增后减的明显变化,在138 K强度出现极大值。分析认为造成原因是由于当温度高于138 K时,高能量的声子分裂成多个具有更低能量的声子所致。     

6H-SiC电子输运的Monte Carlo模拟

从实际测量和单粒子Monte Carlo模拟两个方面研究了6H-SiC的电子输运规律,在模拟中考 虑了6H-SiC主要的散射机理,模拟的结果体现了6H-SiC具有良好的高温和高场特性以及迁移 率的各向异性,其横向迁移率和纵向迁移率相差近5倍.模拟结果和实验数据的对比说明了对 6H-SiC输运特性的模拟是正确的. 关键词： 6H-SiC Monte Carlo模拟 迁移率 散射机理     

碳化硅中惰性气体离子辐照引起缺陷的研究

综述了有关碳化硅材料中惰性气体离子引起辐照缺陷研究的进展。包括借助多种方法对氦离子辐照的碳化硅中氦泡集团形成的剂量阈值的实验研究,基于过冷固体假设对氦泡阈值的理论解释,不同剂量氦泡的两种形态及其机理的研究,以及重惰性气体离子（Ne,Xe）辐照下缺陷演化的特点。This paper gives a review of our recent studies on the defect production in silicon carbide induced by energetic inert-gas-ion irradiation. The work includes the study of the dose threshold for helium bubble formation by combining TEM, RBS-channeling and PAS, the theoretical analysis of the dose threshold for bubble formation based on the Frozen-Matrix assumption, two types of bubble arrangement at different dose regions and the study of damage um-ion production behavior in the case of irradiation with heavier inert-gas-ions （ Ne, Xe） as a comparison to heliirradiation.     

高能离子梯度多剂量辐照4H-SiC的微结构及硬度变化研究

为探讨高温高能离子辐照碳化硅后的结构和力学性能随剂量的变化,应用拉曼光谱和纳米压痕技术研究了122 MeV的²⁰Ne⁴⁺离子梯度多剂量辐照后的4H-SiC。研究表明,SiC的相对拉曼强度随剂量的增大呈指数规律下降,并出现了代表无序化Si-C键和同核Si-Si键的散射峰。基于DI/DS模型的初步拟合表明,在低剂量范围内扩展缺陷簇是引起SiC无序化的主要因素,高剂量范围内的无序化则是由离子直接碰撞过程的非晶化和扩展缺陷簇共同引起。辐照后的SiC硬度取决于位错钉扎和共价键断裂的共同作用,在0～4.00 dpa之间硬度随剂量增大而增大,在4.00～8.05 dpa之间硬度随剂量增大而减小,剂量在8.05 dpa时,硬度相比于未辐照区域略高,此时共价键断裂和位错钉扎达到平衡。     

银(Ⅰ)、镉(Ⅱ)4-巯基吡啶配合物的光谱研究

采用常规溶液反应蒸发法以4-巯基吡啶(简写为4-MPy)为有机配体与银、镉的硝酸盐合成了两种金属有机配合物。并利用红外、拉曼、紫外-可见光谱技术对4-MPy及合成的配位化合物进行了研究,对主要红外和拉曼谱带进行了经验归属,并进一步讨论了配体和配合物的特征吸收谱带与配合物结构间的关系。在红外光谱中,配体在1 459cm-1处的吸收峰归属为CC和CN复合振动峰,形成配合物后在两种配合物中,此吸收峰分别向高波数位移至1 464和1 464cm-1。在拉曼光谱中,两种有机配位化合物在1 004和1 008cm-1处归属为环呼吸振动峰、在1 617和1 615cm-1处归属为环伸缩振动峰、在720和720cm-1处归属为β(C—C)和ν(C—S)的复合振动峰,各自十分相似。     

R6G单分子表面增强共振拉曼散射光谱探测研究

以共焦显微系统为平台,研究了不同浓度的R6G银溶胶的表面增强共振拉曼散射(SERRS)光谱, 结果表明不同浓度溶液中的R6G分子表现出了不同的光谱特性。在浓度为10-13mol·L-1的R6G银溶胶中 得到了R6G单分子的表面增强共振拉曼散射光谱,观察到了一些光谱非均匀变化现象,如谱色散、谱线的 强度起伏、拉曼谱的偏振化以及分子的闪烁等,并对这些现象进行了分析,证明得到的是R6G单分子的 SERRS光谱。文章还对单分子检测中的一些关键问题进行了分析与讨论,确定了单分子SERRS光谱检测的 适当条件。     

Effect of 6H-SiC （1120） substrate on epitaxial graphene revealed by Raman scattering

A nonpolar SiC(1120) substrate has been used to fabricate epitaxial graphene (EG). Two EGs with layer numbers of 8-10 (referred to as MLG) and 2-3 (referred to as FLG) were used as representative to study the substrate effect on EG through temperature dependent Raman scattering. It is found that Raman lineshifts of G and 2D peaks of the MLG with temperature are consistent with that of a free graphene predicted by theory calculation, indicating that the substrate influence on the MLG is undetectable. While Raman G peak lineshifts of the FLG to that of the free graphene are obvious, however, its lineshift rate (-0.016 cm^-1/K) is almost one third of that (-0.043 cm^-1/K) of a EG on 6H-SiC (0001) in the temperature range from 300 K to 400 K, indicating a weak substrate effect from SiC (1120) on the FLG. This renders the FLG a high mobility around 1812 cm²- ·V^-1-·s^-1 at room temperature even with a very high carrier concentration about 2.95× 10¹³ cm^-2 (p-type). These suggest SiC (1120) is more suitable for fabricating EG with high performance.     

Mn掺杂6H-SiC的第一性原理研究

本文通过密度泛函理论第一性原理平面波超软赝势计算方法计算了Mn掺杂6H-SiC的电子结构与光学性质。计算结果显示掺杂Mn后的6H-SiC为间接带隙p型半导体,且带隙较本征体有所降低,带隙由2.022 eV降为0.602 eV,电子从价带跃迁所需能量减少。掺杂后的Mn的3d能级在能带结构中以杂质能级出现,提高了载流子浓度,导电性增强。光学性质研究中,掺杂Mn后的介电函数虚部在低能处增加,电子激发态数量增多,跃迁概率增大。掺杂后的光吸收谱能量初值也较未掺杂的3.1 eV扩展到0 eV,反射谱发生红移。由于禁带宽度的降低使得光电导率起始范围得到扩展。     

Compensating defect centres in semi-insulating 6H-SiC

Photoinduced transient spectroscopy (PITS) has been applied to study electronic properties of point defects associated with charge compensation in semi-insulating (SI) 6H-SiC substrates. The photocurrent relaxation waveforms were digitally recorded in a wide temperature range of 20–800 K and in order to extract the parameters of defect centres, a two-dimensional analysis of the waveforms as a function of time and temperature has been implemented. As a result, the processes of thermal emission of charge carriers from defect centres were seen on the spectral surface as the folds, whose ridgelines depicted the temperature dependences of emission rate for detected defect centres. The new approach was used to compare the defect levels in vanadium-doped and vanadium-free (undoped) SI 6H-SiC wafers.     

6H-SiC的A_1(LO)拉曼峰低温温度特性研究

对6H-SiC单品体材料进行了从80到320 K的低温变温拉曼光谱测量,从实验得到的谱图上指认了部分6H-SiC的折叠拉曼峰,重点利用三声子模型和四声子模型分析了A1(LO)光学声子模峰位和线宽在低温下随温度的变化特性.实验发现,随着温度降低,LO声子模谱峰中心向高波数移动,线宽减小;同时发现当温度低于160 K时,无论足谱峰中心位置还是线宽的变化都趋于平缓,这是在常温和高温下观察不到的,说明在160 K以下时A1(LO)谱线线宽是由声子本身的性质决定,温度对线宽的影响几乎可忽略;理论拟合表明,四声子模型更能与实验数据相符,三次、四次非谐振动共同作用,前者是主要过程;温度越低,A1(LO)光学声子寿命越长,这是由于原子热运动的剧烈程度随温度降低而下降,声子弛豫减弱.     

Determination of the transport properties in 4H-SiC wafers by Raman scattering measurement

The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phonon--plasmon coupled (LOPC) modes, and compared with those determined by Hall-effect measurement and that provided by the vendors. The transport properties of thick and thin 4H-SiC epilayers grown in both vertical and horizontal reactors were also studied. The free carrier density ranges between 2×10¹⁸ cm^-3 and 8×10¹⁸ cm^-3 with a carrier mobility of 30--55 cm²/(V·s) for n-type 4H-SiC substrates and 1×10¹⁶--3×10¹⁶ cm^-3 with mobility of 290--490 cm²/(V·s) for both thick and thin 4H-SiC epilayers grown in a horizontal reactor, while thick 4H-SiC epilayers grown in vertical reactor have a slightly higher carrier concentration of around 8.1×10¹⁶ cm^-3 with mobility of 380 cm²/(V·s). It was shown that Raman spectroscopy is a potential technique for determining the transport properties of 4H-SiC wafers with the advantage of being able to probe very small volumes and also being non-destructive. This is especially useful for future mass production of 4H-SiC epi-wafers.     

6H-SiC辐照特性的低温光致发光研究

本文用低温光致发光(LTPL)技术对经中子辐照的N型6H-SiC在350℃-1650℃温度范围的退火行为进行了研究。在700℃退火后观察到D1中心(D1-center)和位于485.0nm、493.6nm处的发光中心。我们发现D1中心与深能级瞬态谱(DLTS)的E1/E2深能级对具有不同的退火行为,这否定了它们源于相同的辐照诱生缺陷的观点。D1中心可能源于由空位和反位组成的复合体。     

Defects mediated ferromagnetism in a V-doped 6H—SiC single crystal

Undoped and V-doped 6H-SiC single crystals have been grown by the physical vapor transport method.The V concentration is determined to be 3.76×1017 at/cm3 and 6.14×1017 at/cm3 by secondary ion mass spectrometry for low V-doped and high V-doped SiC samples,respectively.The undoped 6H-SiC shows diamagnetism,while the V-doped 6H-SiC exhibits weak ferromagnetism.The lower V-doped sample shows stronger ferromagnetism compared to that of the higher V-doped sample.However,the structural characterization indicates that the lower V-doped SiC has a relative poor crystalline quality.It is found that both V dopants and defects are essential for introducing ferromagnetic exchange in V-doped SiC single crystals.     

Investigation of micropipes in 6H-SiC by Raman scattering

The spectra of 6H-SiC crystals including micropipes have been examined for the Si face using Raman scattering. The first-order Raman features reveal that the intensity of the transverse optical phonon band centered at ∼796 cm⁻¹ is sensitive to the micropipes. And the second-order Raman features of the micropipes in bulk 6H-SiC are well-defined using the selection rules for second-order scattering in wurtzite structure. It is found that there are some second-order peaks missing for the micropipe-including sample, which may be induced by the reduction of the incident laser intensity at around the micropipe, especially the uneven surface in the inner wall of the micropipe. These features might also be employed to characterize other structural defects such as screw-dislocations and threading edge dislocations.