分子束外延生长Fe/Fe_(50)Mn_(50)双层膜的交换偏置

利用表面磁光克尔效应和铁磁共振对分子束外延生长的Fe/Fe50Mn50双层膜的交换偏置场和矫顽力进行了研究,实验结果表明,当反铁磁层厚度小于5.5!nm时,不出现交换偏置,而当大于这一厚度时,出现交换偏置;大约在7!nm时,达到极大值.随着反铁磁层厚度的继续增大,偏置场和矫顽力随Fe50Mn50膜厚的增大而下降.铁磁共振实验结果表明样品的磁性存在单向各向异性.并对上述结果进行了讨论.     

MBE-grown Ridge-waveguide InGaAs/InGaAsP Strained Quantum Well Lasers at 2 μm Wavelength

The result of molecular beam epitaxy (MBE)-grown ridge-waveguide InGaAs/ InGaAsP/InP strained quantum well lasers at 2 μm wavelength is reported. The pulsed electrical luminescence spectrum at room temperature is observed with peak wavelength of about 1.98 μm. At 77 K the lasers become lasing in pulse regime, with threshold current of about 18～30 mA, peak wavelength of about 1.87～ 1. 91 μm, and single longitudinal mode operation in the current range of 160～230 mA.     

Molecular beam epitaxy of Ca1−xRxF2+x (R=Nd, Er) layers: study of RHEED pattern and lattice mismatch

Ca_1−xNd_xF_2+x and Ca_1−xEr_xF_2+x layers were grown on CaF₂(1 1 1) substrates at 600 and 550°C, respectively, by molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) investigation revealed that Ca_1−xNd_xF_2+x layers have two types of surface structure, namely (1×1) and ( )R30⁰ with hexagonal symmetry, depending on Nd mole fraction, while Ca_1−xEr_xF_2+x layers have three types of surface structure, namely (1×1) and (2×2) with hexagonal symmetry, and a triple rotated domain structure based on a rectangular cell depending on Er mole fraction. The lattice mismatch of the epilayers and substrate, which is important for applications involving buffer layers, was measured by X-ray rocking curve (XRC) analysis.     

缓冲层对InSb/GaAs薄膜质量的影响

InSb是制作3~5μm红外探测器的重要材料。在GaAs衬底上外延生长InSb,存在的主要问题在于两种材料间14.6%的晶格失配度,会引入较大的表面粗糙度以及位错密度,使外延材料的结构和电学性能均会受到不同程度的影响。通过系列实验,研究了在生长过程中缓冲层对薄膜质量的影响。利用高能电子衍射仪(RHHEED)得到了合适的生长速率和Ⅴ/Ⅲ比,研究了异质外延InSb薄膜生长中低温InSb缓冲层对材料生长质量以及不同外延厚度对材料电学性质的影响。采用原子力显微镜(AFM)、透射电子显微镜(TEM)、X射线双晶衍射(DCXRD)等方法研究了InSb/GaAs薄膜的表面形貌、界面特性以及结晶质量。通过生长合适厚度的缓冲层,获得了室温下DCXRD半高峰宽为172″,77 K下迁移率为64300 cm²·V^-1·s^-1的InSb外延层。     

Fabrication and microscopic characterization of a single quantum-wire laser with high uniformity

A T-shaped single quantum-wire laser with high spatial uniformity has been fabricated by a cleaved-edge overgrowth method with molecular beam epitaxy and a growth-interrupt annealing technique. Using micro-photoluminescence imaging and spectroscopy, we confirmed the formation of a spatially uniform quantum wire over 20 μm long without hetero-interface roughness. By optical pumping, we achieved single-mode lasing from the ground state of the single quantum wire at a threshold excitation power as low as 5 mW at 5 K.     

A novel method for positioning of InAs islands on GaAs (1 1 0)

A novel method for positioning of InAs islands on GaAs (1 1 0) by cleaved edge overgrowth is reported. The first growth sample contains strained In_xGa_1−xAs/GaAs superlattice (SL) of varying indium fraction, which acts as a strain nanopattern for the cleaved-edge overgrowth. Atoms incident on the cleaved edge will preferentially migrate to InGaAs regions where favorable bonding sites are available. By this method InAs island chains with lateral periodicity defined by the thickness of InGaAs and GaAs of SL have been realized by molecular beam epitaxy (MBE). They are observed by means of atomic force microscopy (AFM). The strain nanopattern's effect is studied by the different indium fraction of SL and MBE growth conditions.     

SiO2/Si衬底上石墨烯的制备与结构表征

在分子束外延(MBE)设备中,利用直接沉积C原子的方法在覆盖有SiO₂的Si衬底(SiO₂/Si)上生长石墨烯,并通过Raman光谱和近边X射线吸收精细结构谱等实验技术对不同衬底温度(500℃,600℃,700℃,900℃,1100℃,1200℃)生长的薄膜进行结构表征.实验结果表明,在衬底温度较低时生长的薄膜是无定形碳,在衬底温度高于700℃时薄膜具有石墨烯的特征,而且石墨烯的结晶质量随着衬底温度的升高而改善,但过高的衬底温度会使石墨烯质量降低.衬底温度为1100℃时结晶质量最好.衬底温度较低时C原子活性较低,难以形成有序的C-sp²六方环.而衬底温度过高时(1200℃),衬底表面部分SiO₂分解,C原子与表面的Si原子或者O原子结合而阻止石墨烯的形成,并产生表面缺陷导致石墨烯结晶变差.     

温度对p-InN薄膜光电导灵敏度的影响

研究了p型InN的光电导效应。利用分子束外延技术(MBE)法生长出高质量的InN薄膜,在此基础上利用Mg掺杂获得了p-InN。原位反射高能电子衍射(RHEED)表明样品在生长过程中保持二维生长模式,原子力显微镜(AFM)测试结果显示台阶流的生长模式。实验发现,p型InN的光电导灵敏度随温度的升高而降低。其主要原因是当温度升高时,光生载流子浓度降低和样品背景浓度升高共同造成的。     

Optical and structural properties of InGaAs/InP double quantum wells grown by molecular beam epitaxy with polycrystalline GaAs and GaP decomposition sources

We report successful growth of high-quality InGaAs/InP double quantum wells (DQWs) with safer and more cost-effective decomposition source molecular beam epitaxy (MBE). The transmission electron microscopy (TEM) images and double crystal X-ray diffraction (TCXD) measurement reveal the formation of abrupt interfaces between InGaAs and InP layers. In the case of optical quality, the line width of 12 K-photoluminescence of the DQWs is 8.2 meV, which is comparable to that of single quantum well grown by MBE with PH₃ cracker and more complex instrument (4 meV).