低温退火对稀磁半导体(Ga,Mn)As性质的影响

利用低温分子束外延技术在GaAs(001)上外延生长出厚度为500nm的稀磁半导体(Ga,Mn)As薄膜.双晶X射线衍射证明其为闪锌矿结构,晶格参数为0.5683nm,据此推导出其Mn含量为7%.磁测量结果揭示其铁磁转变温度为65K.观察了低温退火处理对(Ga,Mn)As磁性质的影响,发现生长后退火处理显著提高了其铁磁转变温度,可以达到115K.     

低温退火对稀磁半导体(Ga,Mn)As性质的影响

利用低温分子束外延技术在GaAs(001)上外延生长出厚度为500nm的稀磁半导体(Ga,Mn)As薄膜.双晶X射线衍射证明其为闪锌矿结构,晶格参数为0.5683nm,据此推导出其Mn含量为7%.磁测量结果揭示其铁磁转变温度为65K.观察了低温退火处理对(Ga,Mn)As磁性质的影响,发现生长后退火处理显著提高了其铁磁转变温度,可以达到115K.     

Mn~+离子注入GaAs的铁磁性质和结构

报道 Mn+ 离子注入 ( 0 0 1 ) Ga As后经快速退火形成的亚微米铁磁晶粒的性质和结构特性 .磁化强度测量结果显示室温下具有铁磁性 .用透射电子显微镜、X射线能谱和电子衍射分析表明除形成 Mn Ga晶粒外 ,还有含少量 Ga的 Mn As晶粒 .原子力显微镜和磁力显微镜的结果表明在 750— 90 0℃下退火形成的铁磁颗粒以单畴为主     

(Ga,Mn,As)/GaAs的发光谱

利用低能双离子束外延技术 ,在 4 0 0℃条件下生长样品 (Ga,Mn,As) / Ga As.样品光致发光谱出现三个峰 ,即1.5 0 4 2 e V处的 Ga As激子峰、1.4 875 e V处的弱碳峰和低能侧的一宽发光带 .宽发光带的中心位置在 1.35 e V附近 ,半宽约 0 .1e V.在 84 0℃条件下对样品进行退火处理 ,退火后的谱结构类似退火前 ,但激子峰和碳杂质峰的峰位分别移至 1.5 0 6 5 e V和 1.4 894 e V,同时低能侧的宽发光带的强度大大增加 .这一宽发射带的来源还不清楚 ,原因可能是体内杂质和缺陷形成杂质带 ,生成 Mn2 As新相 ,Mn占 Ga位或形成 Ga Mn As合金     

我国(Ga,Mn)As磁性半导体研究取得进展

7月9日,《物理评论快报》(Phys.Rev.Lett.111,027203 2013)报道了中科院半导体研究所半导体超晶格国家重点实验室赵建华研究组及合作者在(Ga,Mn)As/Co2FeAl双层膜铁磁界面耦合和磁邻近效应方面取得的最新研究成果。(Ga,Mn)As兼具铁磁体和半导体的性质,过去十多年里受到了高度关     

基于GaAs的新型稀磁半导体材料(Ga,Mn)As

介绍了一种基于 Ga As的新型稀磁半导体材料 ( Ga,Mn) As,包括 ( Ga,Mn) As的制备方法、结构特性、磁性质及磁输运性质。最后 ,展望了 ( Ga,Mn) As的应用前景     

全固源分子束外延生长InP和InGaAsP

在国产分子束外延设备的基础上 ,利用新型三温区阀控裂解源炉 ,对 In P及 In Ga As P材料的全固源分子束外延 (SSMBE)生长进行了研究。生长了高质量的 In P外延层 ,表面缺陷密度为 65cm- 2 ,非故意掺杂电子浓度约为 1× 1 0 16cm- 3.In P外延层的表面形貌、生长速率及 p型掺杂特性与生长温度密切相关 .研究了 In Ga As P外延材料的组分特性 ,发现在一定温度范围内生长温度对 族原子的吸附系数有较大影响 .最后得到了晶格匹配的 In0 .56Ga0 .4 4 As0 .94 P0 .0 6材料 ,低温光致发光谱峰位于 1 50 7nm,FWHM为 9.8me V.     

InP/GaAs异质外延及异变InGaAs光探测器制备

借助超薄低温InP缓冲层,在GaAs衬底上生长出了高质量的InP外延层,在InP外延层中插入了15周期In0.93Ga0.07P/InP应变层超晶格(SLS),进一步阻断了失配位错穿透到晶体表面,提高了外延层的晶体质量,这样2.5 μm厚InP外延层的双晶X射线衍射(DCXRD)ω扫描半高全宽(FWHM)值降低至219 arcsec,该InP外延层的室温光荧光(PL)谱线宽度仅为42 meV.在此基础上,只利用超薄低温InP缓冲层技术就在半绝缘GaAs衬底上成功地制备出了长波长异变In0.53Ga0.47As PIN光电探测器,器件的台面面积为50 μm×50 μm,In0.53Ga0.47As吸收层厚度为300 nm,在3 V反偏压下器件的3 dB带宽达到了6 GHz,在1 550 nm波长处器件的响应度达到了0.12 A/W,对应的外量子效率为9.6%.     

分子束外延生长高应变单量子阱激光器

采用分子束外延方法研究了高应变 In Ga As/Ga As量子阱的生长技术 .将 In Ga As/Ga As量子阱的室温光致发光波长拓展至 116 0 nm,其光致发光峰半峰宽只有 2 2 me V.研制出 112 0 nm室温连续工作的 In Ga As/Ga As单量子阱激光器 .对于 10 0 μm条宽和 80 0 μm腔长的激光器 ,最大线性输出功率达到 2 0 0 m W,斜率效率达到 0 .84m W/m A,最低阈值电流密度为 45 0 A/cm2 ,特征温度达到 90 K.     

GaAlAs/GaAs单量子阱列阵半导体激光器

分析了影响列阵半导体激光器输出功率的因素。利用分子束外延生长法生长出 Ga Al As/Ga As梯度折射率分别限制单量子阱材料 ( GRIN- SCH- SQW)。利用该材料制作出的列阵半导体激光器输出功率达到 10 W(室温 ,连续 ) ,峰值波长为 80 6～ 80 9nm     

Magnetic and magnetotransport properties in the n-type (Ga,Mn)N thin films

We present the magnetic and magnetotransport properties of epitaxial (Ga,Mn)N films with nominal Mn concentration (x=0.1–0.73%) grown by plasma-enhanced molecular beam epitaxy (PEMBE). X-ray diffraction (XRD) reveals that (Ga,Mn)N has the single-phase wurtzite structure without secondary phases. The epitaxial (Ga,Mn)N films were found to exhibit n-type conductivity, ferromagnetic ordering with Curie temperature in the range 550–700 K, and in-plane magnetic anisotropy. The negative magnetoresistance (MR) was observed at temperatures below 50 K and was found to gradually increase with decreasing temperature.     

Effect of thermal annealing on the photoluminescence of structures with InGaAs/GaAs quantum wells and a low-temperature GaAs layer δ-doped with Mn

The effects of isochronal thermal annealing (at 325–725°C) on the radiative properties of InGaAs/GaAs nanoheterostructures containing a low-temperature GaAs layer δ-doped with Mn grown by laser deposition are studied. A decrease in the photoluminescence intensity and increase in the ground transition energy are observed upon thermal impact for quantum wells located near the low-temperature GaAs layer. The distribution of Mn atoms in the initial and annealed structures is obtained by secondary-ion mass spectrometry. A qualitative model of the observed effects of thermal annealing on the radiative properties of the structures is discussed; this model takes into account two main processes: diffusion of point defects (primarily gallium vacancies) from the GaAs coating layer deep into the structure and Mn diffusion in both directions by the dissociation mechanism. Magnetization studies show that, as a result of thermal annealing, an increase in the proportion of the ferromagnetic phase at room temperature (presumably, MnAs clusters) in the low-temperature GaAs coating layer takes place.     

The structure and magnetic properties of β-(Ga0.96Mn0.04)2O3 thin film

High quality epitaxial single phase (Ga0.96Mn0.04)2O3 and Ga2O3 thin films have been prepared on sapphire substrates by using laser molecular beam epitaxy (L-MBE).X-ray diffraction results indicate that the thin films have the monoclinic structure with a (-201) preferable orientation.Room temperature (RT) ferromagnetism appears and the magnetic properties of β-(Ga0.96Mn0.04)2O3 thin film are enhanced compared with our previous works.Experiments as well as the first principle method are used to explain the role of Mn dopant on the structure and magnetic properties of the thin films.The ferromagnetic properties are explained based on the concentration of transition element and the defects in the thin films.     

Coupling of Micromagnetic and Structural Properties Across the Martensite and Curie Temperatures in Miniaturized Ni‐Mn‐Ga Ferromagnetic Shape Memory Alloys

Micromagnetic structure evolution in Ni‐Mn‐Ga ferromagnetic shape memory thin films is investigated by means of temperature dependent magnetic force microscopy (TD‐MFM). The center of interest is the magnetic properties of epitaxial Ni‐Mn‐Ga thin films on MgO substrates across thermally induced phase transitions. Experimental results are discussed within the framework of competing magnetic interactions arising in stressed thin ferromagnetic films. Measurements on 14M martensite specimens are supplemented by three‐dimensional micromagnetic simulations. Corresponding calculated MFM micrographs are compared to experimental data. The influence of twin variant dimension and orientation on micromagnetic domain formation and wall structure is depicted from a theoretical point of view. A micromagnetic model system of partial flux closure is proposed and calculated analytically to estimate a stress induced magneto crystalline anisotropy constant in austenite Ni‐Mn‐Ga.     

Tunneling Anisotropic Magnetoresistance-Based Devices

The paper demonstrates the operation of several devices based on tunneling anisotropic magnetoresistance. This effect, which originates from the interplay between the magnetic and transport properties in magnetic materials with strong spin-orbit coupling such as the ferromagnetic semiconductor (Ga,Mn)As, leads to a dependence of the tunneling resistance of devices with respect to the direction of the magnetization in the (Ga,Mn)As layer. We show that such devices can be operated as either information storage elements or sensors. It was also demonstrated that they can be used in either volatile or nonvolatile mode and that they provide either two-state or multiple state devices in either of these modes. Lastly, we present experimental evidence that they can be coupled to traditional ferromagnetic materials to still further enhance the variety of possible device functionalities     

Magnetic properties of Co- and Mn-implanted BaTiO3, SrTiO3 and KTaO3

Implantation of Co or Mn into single-crystal BaTiO₃(K), SrTiO₃ or KTaO₃(Ca), followed by annealing at 700 °C, produced ferromagnetic behavior over a broad range of transition metal concentrations. For BaTiO₃, both Co and Mn implantation produced magnetic ordering temperatures near 300 K with coercivities 70 Oe. The M–T plots showed either a near-linear decrease of magnetization with increasing temperature for Co and a non-Brillouin shaped curve for Mn. No secondary phases were detected by high-resolution X-ray diffraction. The same basic trends were observed for both SrTiO₃ and KTaO₃, with the exception that at high Mn concentrations (5 at.%) the SrTiO₃ was no longer ferromagnetic. Our results are consistent with recent reports of room temperature ferromagnetism in other perovskite systems (e.g. LaBaMnO₃) and theoretical predictions for transition metal doping of BaTiO₃ [Nakayama et al., Jap. J. Appl. Phys. 40 (2001) L1355].     

Formation of (Ga,Mn)As nanowires and study of their magnetic properties

The molecular-beam epitaxy technique is used to synthesize arrays of (Ga,Mn)As nanowire crystals on a GaAs (111)B surface in the growth-temperature range 480–680°C. It is established that the formation of (Ga,Mn)As nanowires can be described in the context of a vapor-liquid-crystal mechanism. It is shown that the growth of (Ga,Mn)As nanowires must occur in conditions stabilized with respect to Ga. It is found that the field and temperature dependences of the static magnetic susceptibility for samples produced at the temperature 660°C exhibit paramagnetic behavior.     

Magnetic anisotropy in (Ga,Mn)As on GaAs(1 1 3)As studied by magnetotransport and ferromagnetic resonance

The magnetic anisotropy of a 40-nm-thick (Ga,Mn)As film with 5% Mn grown on GaAs(1 1 3)A is studied by means of magnetotransport and ferromagnetic resonance (FMR) spectroscopy. In addition to the cubic and a weak uniaxial in-plane anisotropy, two uniaxial out-of-plane contributions along [1 1 3] and [0 0 1] are found. Using the anisotropy parameters determined from FMR, the longitudinal and transverse resistivities measured as a function of magnetic field orientation and strength are well modelled within the framework of a single ferromagnetic domain. In particular, the low-field data which are strongly affected by sudden jumps of the magnetization are well reproduced.     

La0.7Ca0.3MnO3多晶薄膜的sol-gel法制备及表征

以La、Ca、Mn的无机盐替代相应的醇盐,以冰乙酸为溶剂,乙酰丙酮(AcAc)为螯合剂,采用sol-gel法在Si(110)衬底上制备了La0.7Ca0.3MnO3(LCMO)多晶薄膜,并用FTIR、XRD、SEM、EDS和TEM等分析手段对薄膜进行了表征,通过不同磁场下电阻一温度(R-T)曲线,研究了样品的输运性质及...     

Effects of Doping Mn on Nd_(1.85)Ce_(0.15)CuO_4 System

Nd1.85Ce0.15Cu1-xMnxO4 samples with doping level up to 20% have been synthesized by solid-state reaction method. The influence of Mn on their normal-state transport, crystal structure, superconductivity and magnetic properties has been investigated. For the samples with x〉0.03, magnetization under zero-field cooling indicates that the magnetic state changes from ferromagnetic to paramagnetic at T≈100 K, which can be explained with the interaction between Mn4＋and Mn3＋. The electrical resistivity p of samples increases with Mn doping. For the samples with doping level lower than 0.20, p initially increases with the decrease of temperature, i.e., dp/dt〈0, and then shows superconductivity transition at ≈20 K. The results suggest the coexistence of superconductivity and ferromagnetic ordering in Mn doped Nd1.85Ce0.15CuO4.