MOCVD-Grown AlGaN/AlN/GaN HEMT Structure with High Mobility GaN Thin Layer as Channel on SiC

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with a high-mobility GaN thin layer as a channel are grown on high resistive 6H-SiC substrates by metalorganic chemical vapor deposition. The HEMT structure exhibits a typical two-dimensional electron gas (2DEG) mobility of 1944cm2/(V · s) at room temperature and 11588cm2/(V· s) at 80K with almost equal 2DEG concentrations of about 1.03 × 1013 cm-2 High crystal quality of the HEMT structures is confirmed by triple-crystal X-ray diffraction analysis. Atomic force microscopy measurements reveal a smooth AlGaN surface with a root-mean-square roughness of 0. 27nm for a scan area of 10μm × 10μm. HEMT devices with 0.8μm gate length and 1.2mm gate width are fabricated using the structures. A maximum drain current density of 957mA/mm and an extrinsic transconductance of 267mS/mm are obtained.

低能碳离子束沉积（111）织构的立方SiC薄膜

在硅衬底上利用具有质量选择功能的低能离子束沉积技术沉积碳离子制备出除碳、硅之外无其他杂质元素的纯净的立方SiC薄膜．利用X射线光电子谱、俄歇电子能谱、X射线衍射对样品进行了表征．结果显示常温和400℃制备的样品为非晶结构，在800℃制备的样品由一富碳的表面层和有着良好化学计量比的SiC层组成，碳化硅晶体薄膜是（111）织构的．通过分析可知衬底温度、离子沉积能量和样品保温扩散时间等因素综合在一起对于在硅上沉积SiC薄膜起着重要作用．远远大于TRIM预测厚度的SiC薄膜的获得是高的衬底温度、一定注入能量的碳离子引起的增强扩散以及通道注入效应综合作用的结果。

Homoepitaxial Growth of 4H-SiC and Ti/4H-SiC SBDs

Homoepitaxial growth of4H-SiC on off-oriented Si-face （0001） 4H-SiC substrates was performed at 1500℃ by using the step controlled Epitaxy. Ti/4H-SiC Schottky barrier diodes （SBDs） with blocking voltage over lkV have been made on an undoped epilayer with 32μm in thick and 2-5 × 10^15 cm^-3 in carrier density. The diode rectification ratio of forward to reverse （defined at ± 1V） is over 107 at room temperature and over 10^2 at 538K. Their electrical characteristics were studied by the current-voltage measurements in the temperature range from 20 to 265 ℃. The ideality factor and Schottky barrier height obtained at room temperature are 1.33 and 0. 905eV, respectively. The SBDs have on-state current density of 150A/cm^2 at a forward voltage drop of about 2.0V. The specific on-resistance for the rectifier is found to be as 7.9mΩ · cm^2 and its variation with temperature is T^2.0.

水平冷壁CVD生长4H-SiC同质外延膜

采用自行设计的水平冷壁低压化学气相沉积(LPCVD)方法在偏向〈1120〉晶向8°的n型4H-SiC(0001)衬底上进行了同质外延生长.在5.3×103Pa的低压下,外延膜生长速率超过3μm/h.电容-电压法测试表明在非有意掺杂外延膜中净施主浓度为8.4×10 15cm-3.Nomarski显微镜观察表明厚外延膜的表面光滑,生长缺陷密度很低.AFM测试显示表面均方根粗糙度为0.3nm,没有观察到宏观台阶结构.Raman谱线清晰锐利,表现出典型的4H-SiC特征.在低温PL谱中,近带边区域出现很强的自由激子峰,表明样品是高质量的.

非晶硅碳(a-SiC:H)薄膜光学常数的透射谱表征

报道了一种用透射谱数据分析法计算非晶硅碳薄膜的厚度、折射率、吸收系数和光学带隙等光学常数的方法和程序.这一方法引用有效谐振子模型理论的折射率色散关系,所有公式均为解析表达式,便于进行数据处理,无须专用软件,使用Excel即可完成,适用于多种半导体薄膜材料.将这种方法应用于PECVD方法制备的非晶硅碳(a-SiC∶H)薄膜,对其光学特性进行了分析.

氢稀释对非晶硅碳(a-SiC:H)合金薄膜生长和光学特性的影响

用PECVD方法,以固定的甲烷硅烷气体流量比([CH4]/[SiH4]=1.2)和不同的氢稀释比(RH=[H2]/[CH4+SiH4]=12,22,33,102和135)制备了一系列的氢化非晶硅碳合金(a-SiC:H)薄膜.运用紫外-可见光透射谱(UV-VIS)、红外吸收谱(IR)、Raman谱以及光荧光发射谱(PL)测量研究了氢稀释和高温退火对薄膜生长和光学特性的影响.实验发现氢稀释使薄膜光学带隙展宽(从1.92到2.15 eV).高氢稀释条件下制备的薄膜经过1250℃退火后在室温下观察到可见光发光峰,峰位位于2.1 eV.结合Raman谱分析,认为发光峰源于纳米硅的量子限制效应,纳米硅被Si-C和Si-O限制.

厚表层Si柔性绝缘衬底上SiC薄膜的外延生长

利用LPCVD方法,在厚表层Si(SOL≈0.5μm)柔性绝缘衬底(SOI)(001)上外延生长出了可与硅衬底上外延晶体质量相比拟的SiC/SOI,表明SOI是一种很有潜力的柔性衬底. Raman 光谱结果表明SiC/SOI外延层比SiC/Si外延层有更大的残存应力,对此从理论上进行了解释.利用X射线衍射(XRD)、原子力显微镜(AFM)、扫描电镜(SEM)和喇曼散射光谱(RAM)技术研究了外延材料的晶体结构、界面性质和应变情况.

Second-Order Raman Scattering from n- and p-Type 4H-SiC

The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigned to particular phonon branches and the points in the Brillouin zone from which the scattering originates.There exists a doublet at 626/636cm-1 with energy difference about 10cm-1 in both n- and p-type 4H-SiC,which is similar to the doublet structure with the same energy difference founded in hexagonal GaN,ZnO, and AlN.The cutoff frequency at 1926cm-1 of the second-order Raman is not the overtone of the A1(LO) peak of the n-type doping 4H-SiC,but that of the undoping one.The second-order Raman spectrum of 4H-SiC can hardly be affected by doping species or doping density.

Homoepitaxial Growth and Characterization of 4H-SiC Epilayers by Low-Pressure Hot-Wall Chemical Vapor Deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get highly qualitical 4H-SiC epilayers.Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates is performed at 1500℃ with a pressure of 1.3×103Pa by using the step-controlled epitaxy.The growth rate is controlled to be about 1.0μm/h.The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope,atomic force microscopy (AFM),X-ray diffraction,Raman scattering,and low temperature photoluminescence (LTPL).N-type 4H-SiC epilayers are obtained by in-situ doping of NH3 with the flow rate ranging from 0.1 to 3sccm.SiC p-n junctions are obtained on these epitaxial layers and their electrical and optical characteristics are presented.The obtained p-n junction diodes can be operated at the temperature up to 400℃,which provides a potential for high-temperature applications.

SiC Schottky结反向特性的研究

对Ti/6H-SiC Schottky结的反向特性进行了测试和理论分析,提出了一种综合的包括SiC Schottky结主要反向漏电流产生机理的反向隧穿电流模型,该模型考虑了Schottky势垒不均匀性、Ti/SiC界面层电压降和镜像力对SiC Schottky结反向特性的影响,模拟结果和测量值的相符说明了以上所考虑因素是引起SiC Schottky结反向漏电流高于常规计算值的主要原因.分析结果表明在一般工作条件下SiC Schottky结的反向特性主要是由场发射和热电子场发射电流决定的.

6H－SiC MOS结构电特性及其辐照效应的研究

对SiC MOS结构辐照引起的电参数退化及其电特性进行了研究。结果说明

SiC的光谱特性研究

国家自然科学基金

SiC材料及器件研制的进展

作为第三代的半导体材料—SiC具有禁带宽度大、热导率高、电子的饱和漂移速度大、临界击穿电场高和介电常数低等特点，在高频、大功率、耐高温、抗辐照的半导体器件及紫外探测器和短波发光二极管等方面具有广泛的应用前景。文章综述了半导体SiC材料生长及其器件研制的概况。

随激发波长改变的SiC纳米棒的Raman光谱

用不同波长的激光激发得到了SiC纳米棒的Raman光谱，发现谱的形貌与体材料有很大差别，并且随着激发光的改变出现明显变化，认为是由于受Frohlich相互作用影响而引起的共振现象，并据此对实验结果进行了解释。