Raman Studies of Graphene Films Grown on 4H-SiC Subjected to Deposition of Ni

Semiconductors - Raman spectroscopy is used to evaluate the structural perfection of epitaxial graphene films before and after deposition of a Ni layer to their surface by magnetron sputtering. Two...     

Comparative Studies of Carrier Dynamics in 3C-SiC Layers Grown on Si and 4H-SiC Substrates

Time-resolved nonlinear optical techniques were applied to determine the electronic parameters of cubic silicon carbide layers. Carrier lifetime, τ, and mobility, μ, were measured in a free-standing wafer grown on undulant Si and an epitaxial layer grown by hot-wall chemical vapor deposition (CVD) on a nominally on-axis 4H-SiC substrate. Nonequilibrium carrier dynamics was monitored in the 80 K to 800 K range by using a picosecond free carrier grating and free carrier absorption techniques. Correlation of τ(T) and μ _a(T) dependencies was explained by the strong contribution of diffusion-limited recombination on extended defects in the layers. A lower defect density in the epitaxial layer on 4H-SiC was confirmed by a carrier lifetime of 100 ns, being ~4 times longer than that in free-standing 3C.     

Characterization of Strain Due to Nitrogen Doping Concentration Variations in Heavy Doped 4H-SiC

Highly doped 4H-SiC will show a significant lattice parameter difference with respect to the undoped material. We have applied the recently developed monochromatic contour mapping technique for 4H-SiC crystals to a 4H-SiC wafer crystal characterized by nitrogen doping concentration variation across the whole sample surface using a synchrotron monochromatic x-ray beam. Strain maps of 0008 and ? 2203 planes were derived by deconvoluting the lattice parameter variations from the lattice tilt. Analysis reveals markedly different strain values within and out of the basal plane indicating the strain induced by nitrogen doping is anisotropic in the 4H-SiC hexagonal crystal structure. The highest strain calculated along growth direction [0001] and along [1-100] on the closed packed basal plane is up to ? 4 × 10^?4 and ? 2.7 × 10^?3, respectively. Using an anisotropic elasticity model by separating the whole bulk crystal into numerous identical rectangular prism units, the measured strain was related to the doping concentration and the calculated highest nitrogen level inside wafer crystal was determined to be 1.5 × 10²⁰ cm^?3. This is in agreement with observation of double Shockley stacking faults in the highly doped region that are predicted to nucleate at nitrogen levels above 2 × 10¹⁹ cm^?3.     

基于6H-SiC衬底外延石墨烯的被动锁模掺镱光纤激光器

报道了6H-SiC衬底外延生长的石墨烯作为可饱和吸收体,环形腔结构的全正色散被动锁模掺镱光纤激光器。在注入抽运功率为250mW时,得到稳定的重复频率为1.05MHz的自锁模脉冲,平均输出功率为6mW;当注入抽运功率增加到480mW时,最大平均输出功率为20mW,相应的最高单脉冲能量为19nJ,激光脉冲宽度约为520ps。     

TCE浓度对热氧化制备6H-SiC MOS特性的影响

研究了新型SiCMOS电容的制备工艺。采用干O2+CHCCl3(TCE)热氧化方法生长6H-SiCMOS氧化层。研究了TCE浓度与SiC/SiO2界面态电荷密度和氧化层电荷密度和应力下平带电压漂移的关系,随着TCE浓度的增加,SiC/SiO2界面态电荷密度和氧化层电荷密度先减小后增大,应力下平带电压漂移减小,得出了最佳TCE:O2浓度比。     

4H-SiC衬底AlGaN/GaN高电子迁移率晶体管的研制

报道了在4H-SiC衬底上AlGaN/GaN高电子迁移率晶体管(HEMT)的研制和室温特性测试结果.器件采用栅长为0.7μm,夹断电压为-3.2V,获得了最高跨导为202mS/mm,最大漏源饱和电流密度为915mA/mm的优良性能和结果.     

4H-SiC衬底AlGaN/GaN高电子迁移率晶体管的研制

报道了在4H-SiC衬底上AlGaN/GaN 高电子迁移率晶体管(HEMT)的研制和室温特性测试结果.器件采用栅长为0.7μm,夹断电压为-3.2V,获得了最高跨导为202mS/mm,最大漏源饱和电流密度为915mA/mm的优良性能和结果.     

Comparative Study of Conventional and Quasi-Freestanding Epitaxial Graphenes Grown on 4H-SiC Substrate

Semiconductors - The structural and some other characteristics of quasi-freestanding single-layer graphene obtained by annealing of the buffer layer in the flow of hydrogen are studied in...     

Empirical Study of Hall Bars on Few-Layer Graphene on C-Face 4H-SiC

Hall bars were fabricated on epitaxial graphene formed on 4H-SiC{0001} under various growth environments. Subsequently, they were analyzed via electrical characterization, atomic force microscopy (AFM), Raman mapping, and transmission electron microscopy (TEM) with emphasis on the C-face. The results of the measurement techniques were then corroborated to find correlations. It was found that there is a positive correlation between Hall mobility values and growth pressure in an Ar environment for the C-face. AFM elucidated that topographic features do not correlate with Hall mobility values, nor does device height correlate with carrier concentration. Raman spectroscopy showed that there is a correlation between Hall mobility values and the 2D peak full-width at half-maximum, and a weak correlation with 2D peak position. Additionally, the spectra are sensitive to topographic changes and film discontinuities. Dark-field TEM found higher levels of contrast variation in the SiC〈0001〉 direction, representative of out-of-plane disorder, corresponding to a blue-shift in the 2D peak position. This disorder does not seem to strongly influence Hall mobility values, as it was found in the device with the highest measured Hall mobility: 18,700 cm² V⁻¹ s⁻¹.     

掺氮6H-SiC单晶的电阻率、迁移率及自由载流子浓度

测试了国产和美国Cree公司生产的n型6H-SiC低温下的电学参数,包括电阻率、迁移率和自由载流子浓度,并用FCCS软件数据拟合分析得到两种SiC的杂质浓度和能级.实验结果表明:杂质浓度和补偿度对低温下SiC的电性能有很大影响,轻度补偿的掺氮6H-SiC是施主氮的两个能级共同起作用;而重度补偿的6H-SiC在低温时则是受主能级起作用,并且后者迁移率随温度变化曲线的峰值降低并右移.同时发现重度补偿的SiC在较低温度时由n型转变成了p型,并从理论上分析了产生这种现象的原因.     

掺氮6H-SiC单晶的电阻率、迁移率及自由载流子浓度

测试了国产和美国Cree公司生产的n型6H-SiC低温下的电学参数,包括电阻率、迁移率和自由载流子浓度,并用FCCS软件数据拟合分析得到两种SiC的杂质浓度和能级.实验结果表明:杂质浓度和补偿度对低温下SiC的电性能有很大影响,轻度补偿的掺氮6H-SiC是施主氮的两个能级共同起作用;而重度补偿的6H-SiC在低温时则是受主能级起作用,并且后者迁移率随温度变化曲线的峰值降低并右移.同时发现重度补偿的SiC在较低温度时由n型转变成了p型,并从理论上分析了产生这种现象的原因.     

Electrical and Optical Properties of Stacking Faults in 4H-SiC Devices

By using electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques, we characterized the electrical and optical properties of stacking faults (SFs) in 4H-SiC p ⁺/−n junctions and compared with those in Schottky diodes. In the EBIC images, SFs penetrating the p ⁺/−n junction are bright in the n ⁻ region and dark in the p ⁺ region, while SFs observed in the Schottky diode are only bright. In CL measurements, a characteristic peak (417 nm) appears at SFs in the n ⁻ region, similar to those observed in Schottky diodes. The 417-nm peak, however, does not occur obviously at either the p ⁺ layer or within the depletion region. The reason for the absence of this emission is discussed in terms of band bending at the junction.     

重掺Ⅲ-Ⅴ族化合物半导体载流子浓度的光测法研究

本文应用计算机,绘出各类重掺Ⅲ-Ⅴ族化合物半导体在不同等离子频率ω_p下的反射率曲线,从中找出了反射谱的高低频反射边在反射率极小值处所对应的频率ω_1与ω_2之和与ω_p间的函数关系.并应用此关系对不同载流子浓度的重掺Ⅲ-Ⅴ族化合物半导体GaAs和Inp样品进行实验上的验证,获得了满意的结果.     

载气流量对HVPE外延生长GaN膜光学性质的影响

研究了利用水平氢化物气相外延 (HVPE)系统在蓝宝石衬底上外延氮化镓 (Ga N)的生长规律 ,重点研究了作为载气的氮气流量对 Ga N膜的结构及光学性质的影响。观察到载气流量对预反应的强弱有很大影响 ,外延膜的质量和生长速度对载气流量极为敏感。当载气流量较小时 ,样品的 X射线衍射谱 (XRD)中出现了杂峰(1 0 -1 1 )和 (1 1 -2 0 ) ,相应的光致发光谱 (PL)中出现了黄带 (YL) ,靠近带边有杂质态。而当载气流量增大时 ,样品质量改善。Ga N外延膜的结构和光学性质的相关性表明深能级的黄带与生长过程中产生的非 c轴方向晶面有关 ,据此我们推测 :Ga空位与束缚在 (1 0 -1 1 )和 (1 1 -2 0 )等原子面上的杂质构成复合结构 ,这些复合结构所产生的深能级对黄带的发射有贡献 ;由于预反应使生长过程中混入的附加产物及杂质对带边发射有重要影响     

MBE生长的InSb和InASxSb1—x的载流子浓度剖面分布

在(111)InSb 和(100)GaAs 衬底上,用分子束外延技术生长了 InSb 和 InAs_xSb_(1-x)外延层。用自动电化学 C—V 法测量了外延层的载流子浓度剖面分布。结果表明:(1)外延层呈 P 型;(2)InSb/GaAs 异质外延层的载流子浓度为(1～2)×10~(16)cm~(-3),比相应的同质外延层 InSb/InSb 的(1～2)×10~(17)cm~(-3)小一个数量级;(3)生长层的载流子浓度剖面分布和质量取决于衬底表面的制备。讨论了有关问题。     

Optical and electrical properties of 4H-SiC irradiated with Xe ions

Structures with aluminum-ion-implanted p ⁺-n junctions formed in 26-μm-thick chemicalvapor-deposited-epitaxial 4H-SiC layers with an uncompensated donor concentration N _d ?N _a = (1–3) × 10¹⁵ cm^?3 are irradiated with 167-MeV Xe ions at fluences of 4 × 10⁹ to 1 × 10¹¹ cm^?2 and temperatures of 25 and 500°C. Then as-grown and irradiated structures are thermally annealed at a temperature of 500°C for 30 min. The as-grown, irradiated, and annealed samples are analyzed by means of cathodoluminescence, including the cross-sectional local cathodoluminescence technique, and electrical methods. According to the experimental data, radiation defects penetrate to a depth in excess of several tens of times the range of Xe ions. Irradiation of the structures at 500°C is accompanied by “dynamic annealing” of some low-temperature radiation defects, which increases the radiation resource of 4H-SiC devices operating at elevated temperatures.     

Generation of Defects in Heavily Al-Doped 4H-SiC Epitaxial Layers Grown by the Low-Temperature Halo-Carbon Method

Application of the low-temperature halo-carbon epitaxial growth technique to produce heavily doped p-type epitaxial layers was investigated. While growth at 1300°C facilitated Al incorporation, possible degradation of crystalline quality had to be evaluated. A quantitative measure of the defects generated during epitaxial growth was obtained using molten potassium hydroxide (KOH) etching. The trend with increased doping was for an increase in threading dislocations and Al precipitates. The degradation initially involved an increase in generation of threading dislocations, which was followed at higher doping by generation of defects giving rise to smaller KOH etch pits. The properties of the small-etch-pit defects were reminiscent of Al precipitates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to establish that the small-etch-pit defects were localized at various depths inside the epilayers. Energy-dispersive spectroscopy (EDS) indicated that these small-etch-pit defects contained a higher concentration of aluminum.     

Spatial Localization of Carrier Traps in 4H-SiC MOSFET Devices Using Thermally Stimulated Current

Carrier traps in 4H-SiC metal–oxide–semiconductor (MOS) capacitor and transistor devices were studied using the thermally stimulated current (TSC) method. TSC spectra from p-type MOS capacitors and n-channel MOS field-effect transistors (MOSFETs) indicated the presence of oxide traps with peak emission around 55 K. An additional peak near 80 K was observed due to acceptor activation and hole traps near the interface. The physical location of the traps in the devices was deduced using a localized electric field approach. The density of hole traps contributing to the 80-K peak was separated from the acceptor trap density using a gamma-ray irradiation method. As a result, hole trap density of N _t,hole = 2.08 × 10¹⁵ cm⁻³ at 2 MV/cm gate field and N _t,hole = 2.5 × 10¹⁶ cm⁻³ at 4.5 MV/cm gate field was extracted from the 80-K TSC spectra. Measurements of the source-body n ⁺–p junction suggested the presence of implantation damage in the space-charge region, as well as defect states near the n ⁺ SiC substrate.     

Mapping of Lattice Strain in 4H-SiC Crystals by Synchrotron Double-Crystal X-ray Topography

The presence of lattice strain in n-doped 4H-SiC substrate crystals grown by a physical vapor transport method can strongly influence the performance of related power devices that are fabricated on them. Information on the level and the variation of lattice strain in these wafer crystals is thus important. In this study, a non-destructive method is developed based on synchrotron double-crystal x-ray topography to map lattice strains in 4H-SiC wafers. Measurements are made on two 4H-SiC substrate crystals—one is an unprocessed commercial wafer while the other was subject to a post-growth high-temperature heat treatment. Maps of different strain components are generated from the equi-misorientation contour maps recorded using synchrotron monochromatic radiation. The technique is demonstrated to be a powerful tool in estimating strain fields in 4H-SiC crystals. Analysis of the strain maps also shows that the normal strain components vary much more significantly than do the shear/rotation components, indicating that lattice dilation/compression rather than lattice tilt is the major type of deformation caused by both the incorporation of nitrogen dopants and the nucleation of basal plane dislocations.