Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films

This paper reports that the(Ga,Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition.Room-temperature ferromagnetism is observed for the as-grown thin films.The x-ray absorption fine structure characterization reveals that Co 2+ and Ga 3+ ions substitute for Zn 2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin.The ferromagnetic(Ga,Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature.The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.     

固相反应法制备Co掺杂ZnO的磁性和光学性能研究

研究了以固相反应法制备Co掺杂ZnO粉体的磁性和光学性能，测试结果表明对于均匀掺杂的Zn_0.95Co_0.05O粉体，Co²⁺随机取代Zn²⁺的位置进入ZnO晶格.Co²⁺之间的3d自旋电子耦合交换作用使得近邻的Co²⁺自旋反平行，Zn_0.95Co_0.05O粉体在3—300K表现为顺磁性，而非铁磁性. 关键词： ZnO 固相反应 稀磁半导体 顺磁性     

Fabrication of Ti ohmic contact to n-type 6H-SiC without high-temperature annealing

The effect of surface morphology of 6H-SiC substrate on the ohmic contact properties of Ti/6H-SiC structure is studied. The H-terminated surface on Si-face 6H-SiC is obtained by both dipping SiC into HF acid solution for 15 s and thermal heating SiC in hydrogen atmosphere at 1100 C for 10 min, while the H-terminated surface on C-face 6H-SiC could be obtained only by the latter method. Ti is deposited on Si-face and C-face SiC substrates with H-terminated surfaces and ohmic contact is obtained without high-temperature annealing.     

杂质和缺陷对SiC单晶导热性能的影响

目前关于SiC单晶室温的导热性能,以及导热特性随温度的变化方面的研究报道还存在较大的差异,有关SiC单晶热导率的研究主要是沿c轴<0001>晶向或者垂直于c轴的某一晶向进行的,无法有效地解释热导率的各向异性。本文研究了4H-SiC和6H-SiC单晶目前关于SiC单晶室温的导热性能,以及导热特性随温度的变化方面的研究报道还存在较大的差异,有关SiC单晶热导率的研究主要是沿c轴0001晶向或者垂直于c轴的某一晶向进行的,无法有效地解释热导率的各向异性。本文研究了4H-SiC和6H-SiC单晶■,■,0001三个不同晶向上热导率以及其随温度的变化。对SiC单晶切割分别得到沿■,■,0001晶向的样品,尺寸为■12.7 mm×3 mm,利用闪光法对样品测试得到热扩散系数,通过计算获得了SiC单晶不同晶向的热导率数值,采用辉光放电质谱仪(GDMS)和扫描电子显微镜(SEM)进行了杂质和缺陷表征。实验结果表明,SiC晶体■,■,0001三个晶向的热导率随温度升高而下降,沿0001晶向的SiC样品热导率最小;含有较高杂质离子浓度的6H-SiC样品热导率高于4H-SiC样品;缺陷相比杂质对SiC晶体导热性能影响更大,缺陷是SiC热导率具有各向异性的主要原因。     

Magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn^2＋ for Zn^2＋ without additional acceptor doping. The substitution of N for O （NO^-） is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn^2＋ and Mn^3＋ via NO^-, The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.     

Ⅲ-Ⅵ族InSe半导体晶体生长研究进展

Ⅲ-Ⅶ族InSe晶体是一种非常重要的化合物半导体材料，在高性能纳米电子器件、红外光探测、光电器件及柔性电子等领域有广泛应用。本文简要介绍了In-Se相图的发展历程，InSe具有非一致熔融特性，可通过包晶反应从准化学计量比或非化学计量比溶液中析晶获得，其中In/Se摩尔比对InSe转化率有重要影响。迄今，垂直布里奇曼法、提拉法、水平梯度凝固法、低温液相法及气相输运法等多种技术被成功用于制备InSe晶体。为全面了解InSe晶体生长的历史和现状，本文从工艺原理、技术要点、晶体生长结果等方面将国内外相关工作进行了梳理，并对各种方法的优缺点进行了比较。研究分析表明垂直布里奇曼法因对设备要求简单，操作简易，现已成为制备高质量大尺寸InSe晶体的主流技术；水平梯度凝固法则在ε型InSe晶体生长方面颇具特色，未来可在新材料性能研究与应用探索上与垂直布里奇曼法形成一定补充。     

Co掺杂ZnO薄膜的局域结构和电荷转移特性研究

采用磁束缚电感耦合等离子体溅射沉积法在不同的氧气分压下制备了Zn_0.95Co_0.05O和Zn_0.94Co_0.05Al_0.01O薄膜.利用X射线吸收精细结构技术对薄膜O-K,Co-K和Co-L边进行了局域结构研究,结果表明：Co²⁺取代了四配位晶体场中的Zn²⁺而未改变ZnO的六方纤锌矿结构,高真空条件下制备的薄膜 关键词： Co掺杂ZnO 稀磁半导体 X射线吸收精细结构 共振非弹性X射线散射     

Difference in magnetic properties between Co-doped ZnO powder and thin film

This paper reports that the Zn掺钴;氧化锌粉末;氧化锌薄膜;磁性差异;晶体取向ZnO, Co-doped, crystalline orientation, magnetismProject supported by the Shanghai Nanotechnology Promotion Center (Grant No~0452nm071).2006-09-152006-11-29This paper reports that the Zn0.95Co0.05O polycrystalline powder and thin film were prepared by sol-gel technique under the similar preparation conditions. The former does not show typical ferromagnetic behaviour, while the latter exhibits obvious ferromagnetic properties at 5 K and room temperature. The UV-vis spectra and x-ray absorption spectra show that Co2＋ ions are homogeneously incorporated into ZnO lattice without forming secondary phases.The distinct difference between film and powder sample is the c-axis （002） preferential orientation indicated by the x-ray diffraction pattern and field emission scanning electron microscopy measurement, which may be the reason why Zn0.95Co0.05O film shows ferromagnetic behaviour.     

Effects of annealing temperature on the electrical property and microstructure of aluminum contact on n-type 3C–SiC

The 3C-SiC thin films used herein are grown on Si substrates by chemical vapor deposition. A1 contacts with differ- ent thickness values are deposited on the 3C-SiC/Si （100） structure by the magnetron sputtering method and are annealed at different temperatures. We focus on the effects of the annealing temperature on the ohmic contact properties and mi- crostructure of A1/3C-SiC structure. The electrical properties of A1 contacts to n-type 3C-SiC are characterized by the transmission line method. The crystal structures and chemical phases of A1 contacts are examined by X-ray diffraction, Raman spectra, and transmission electron microscopy, respectively. It is found that the A1 contacts exhibit ohmic contact behaviors when the annealing temperature is below 550 ℃, and they become Schottky contacts when the annealing tem- perature is above 650 ℃. A minimum specific contact resistance of 1.8 × 10-4 Ω cm2 is obtained when the A1 contact is annealed at 250 ℃.     

V掺杂6H-SiC光导开关制备与性能研究

采用V掺杂半绝缘6H-SiC单晶衬底材料制备了平面电极型大功率SiC光导开关,用强度为150μJ/mm2、波长为355nm的脉冲激光对开关进行触发,在1~14kV的外加电压范围内对光导开关的耐压特性、导通电阻等性能进行了研究。结果表明:随着开关外加电压的升高,开关的电流峰值呈现不断增大的趋势,当开关外加电压为14kV时,电流峰值达185A,对应的光导开关峰值功率为2.59MW,开关的导通电阻约为22Ω。