掺Be分子束外延GaAs的喇曼光谱

利用喇曼光谱研究了掺Be分子束外延P型GaAs中晶格振动的纵光学声子LO与空穴等离子体激元的耦合.观测了耦合模L_+与L_-的喇曼光谱及其谱峰强度和位置随不同空穴浓度的变化,并对谱图进行了分析和讨论.     

纳米碳管模板法制取的GaP纳米棒拉曼光谱研究

报道了用纳米碳管模板法制备的GaP纳米棒的拉曼光谱特征，观测到声子限制效应引起的GaP纳米棒TO和LO模的红移，红移量一般在2－10cm^-1之间，与所测到的纳米棒的尺寸有关，在偏振特性研究中，发现GaP纳米棒的偏振特性不能用单根纳米棒的选择定则来解释，而与测量光斑内多根纳米棒的无序取向有关，无序程度越高，偏振特性的方向性越弱，当激发光功率增加时，GaP纳米棒的TO和LO模的频率显著减少，表明纳米棒中的激光加热效应比体材料中强很多，而且GaP纳米棒的拉曼散射强度随激发光功率的增加先饱和，然后减小，表明在强激发功率下GaP纳米棒中的缺陷会迅速增加。     

p型重掺杂应变Si_(1-x)Ge_x层中少子常温和低温行为

采用解析的方法计算了少数载流子浓度与Ge组分x、温度T以及掺杂浓度N的关系。发现常温时,在同一掺杂浓度下,少子浓度随Ge组分的增加而增大,其增加的速度越来越快;在同一Ge组分下,少子浓度随掺杂浓度的增加而减少,其减少的速度越来越慢。低温下,在考虑杂质不完全电离的同时,对由非简并情形向简并情形过渡的杂质电离出来的空穴浓度进行了修正,发现在同一Ge组分下,少子浓度随掺杂浓度的增加而增大,其增加的速度变得越来越快。同一掺杂浓度下,少子浓度随Ge组分的增加而增大,其增加的速度,轻掺杂时增加的较慢,重掺杂时增加得越来越快。     

MOCVD生长AlGaInN外延层的光学性质研究

对AlInGaN四元合金进行了微区发光和拉曼散射研究．根据V-形缺陷周围扫描电镜图像和阴极荧光光谱的分析，确定AlInGaN外延层中V-形缺陷的形成与铟的分凝之间的关系．同时，用波长为325纳米的短波长激光研究了AlInGaN外延薄层的拉曼散射，测量了合金铝组分改变引起的A1(LO)声子的频率移动，观测到了出射共振引起的LO声子拉曼散射谱的共振加强，此共振过程的机制是一种类级联的电子-多声子互作用机制．     

合金无序和界面不平整对InGaAs/GaAs应变量子阱光谱展宽的影响

用光荧光和光吸收的实验方法研究了InGaAs/GaAs应变量子阱低温下的光谱展宽机理。实验观察到激子谱线半宽随着InGaAs层厚度和In的组分增加而增大。采用有效晶体近似的方法分析了实验数据,发现样品中合金组合无序引起的激子谱线展宽是主要的光谱展宽机理。实验中还发现与轻空穴有关的吸收光谱结构在升温过程中由吸收峰变为台阶状的谱结构。该现象可用与轻空穴有关的吸收为空间间接跃过来解释。     

线性分布的In组分对紫色InGaN/GaN单量子阱发光特性的影响

采用数值模拟的方法研究了具有相同的平均In组分,但In组分的分布不同的3个紫色InGaN/GaN单量子阱样品的光谱特性.通过分析样品的电致发光谱、能带结构、波函数交叠以及载流子浓度分布等,发现沿生长方向阱内In组分线性增加的单量子阱样品的发光效率最高,而In组分线性减小的样品发光效率最低.这是因为In组分的线性增加能够减弱极化场对价带的影响,使阱内价带变得更加平缓.这不仅降低了空穴的注入势垒高度、增大了阱中的空穴浓度,还增强了阱内电子-空穴波函数的交叠积分,提高了辐射复合几率,从而使In组分线性增加的量子阱的发光效率显著提高.     

GaP1-xNx混晶的喇曼散射谱

在室温下测试了GaP1-xNx(x=0.05%～3.1%)混晶的喇曼散射谱.在一级喇曼散射谱中观测到了GaP的LO(Γ)模和强度较弱的禁戒TO(Γ)模以及N的局域模(495cm-3).在N组分较高的一组样品(x=1.3%～3.1%)中,还观察到了位于GaP的LO(Γ)模和TO(Γ)模之间的由N导致的LO(N)模的喇曼频移(387cm-1),其强度随着N浓度的增加而增强.在二级喇曼散射谱中,除了观测到布里渊区中心的声子散射峰2LO(Γ)外,还观测到了布里渊区边界的声子散射峰2LO(L)、2TO(X)以及LO(L)+TO(X).且边界散射峰的强度比中心散射峰更强.另外在组分x=0.6%和x=0.81%的样品中,还得到了诸如来自不同NNi对或N原子簇团的局域模和由N导致的新的散射峰.     

氮化镓薄膜中LO声子—等离子体激元耦合模拉曼光谱研究

对生长在蓝宝石衬底上不同Si掺杂浓度的一系列GaN外延膜进行了拉曼散射光谱测量，观察到清晰的LO声子－等离子体激元耕合模的高频支（LPP＋）和低频支（LPP－）及其随掺杂浓度的增加往高频方向的移动，通过进行理论计算和拟合，得到GaN中的等离子体激元的频率及阻尼常数，并由此计算得到GaN中的载流子浓度和迁移率，与红外反射谱测量得到的数据进行了比较，结果表明，2种光谱方法得到的载流子浓度均与霍耳测量相一致。但迁移率比霍耳迁移率要低，接近杂质散射机制下的漂移迁移率。     

Hg_(1-x)Cd_xTe的拉曼光谱

我们发现Hg1 -xCdxTe的拉曼散射峰随着温度的变化会发生频移 ,它的二级散射峰来自LO1 LO1 ,LO1 LO2 ,LO2 LO2 ,并且它们的强度对晶体的完整性较敏感。同时也发现Hg1 -xCdxTe中的Te的沉淀相和Te的氧化物相的拉曼散射峰。     

InGaN:Mg薄膜的电学特性研究

利用MOCVD生长了InGaN:Mg薄膜,研究了生长温度、掺Mg量对InGaN:Mg薄膜电学特性的影响.结果表明,空穴浓度随着生长温度的降低而升高.在相同的生长温度下,空穴浓度随掺Mg量的增加,先升高后降低.通过对这两个生长条件的优化,在760℃、CP2Mg与TMGa摩尔流量之比为2.2‰时制备出了空穴浓度高达2.4×1019cm-3的p-InGaN:Mg薄膜.这对进一步提高GaN基电子器件与光电子器件的性能有重要意义.     

Effect of p-d exchange with an itinerant carrier in a GaMnAs quantum dot

Hydrogenic acceptor binding energy as a function of dot radius in a GaMnAs/Ga_0.6Al_0.4As quantum dot is calculated including the exchange interaction of Mn alloy content with an itinerant carrier.Calculations are performed by varying its dot radius,for various Mn alloy contents in GaMnAs quantum dot within a single band effective mass approximation using variational method.The spin polaronic energy of the acceptor impurity for different Mn²⁺ is evaluated for different dot radii using a mean field theory in the presence of magnetic field strength.The magnetization is computed in the influence of magnetic field and the Mn ions.The effective g-factor of the valence band electron with the inclusion of effects of Mn ion impurities is found in the influence of the magnetic field.The exchange coupling constant is calculated for various magnetic field strengths.The results show that the p-d exchange interaction in the GaMnAs/Ga_0.6Al_0.4As quantum dot has a strong dependence on spatial confinement,effect of magnetic field strength and the Mn alloy content.Our results are in good agreement with the other investigators.     

Study of photoluminescence spectra of GaMnAs produced by low-temperature molecular beam epitaxy

The luminescence spectra of the GaMnAs layers produced by low-temperature molecular beam epitaxy are studied at temperatures ranging from 4 to 150 K. In the spectra of the GaMnAs layers containing the MnAs clusters, local peaks at the energies of 1.36 and 1.33 eV are observed. It is shown that the red shift of the excitonic luminescence line depends on the Mn content in the semiconductor matrix.     

Spintronics

Recent successes by a Nottingham University group includes the growth of GaMnAs material with world record Curie temperatures, and ferromagnetic TiCoO2 and GaMnN which shows ferromagnetism at room temperature. A characteristic of the GaMnAs layers grown by the group is their low resistivity that is accompanied by very weak high field magneto-resistance. This has enabled the group to separate the normal and anomalous contributions to the Hall effect and make the first accurate measurements of hole densities across a range of Mn compositions. Using this information the first meaningful comparison of theoretically predicted Curie temperatures and extraordinary Hall conductivities with experiment have been made. The samples were grown by Low Temperature Molecular Beam Epitaxy (LTMBE) technique. The In composition of InGaAs superlattice spacers and InGaMnAs magnetic layers was chosen to be equal to 50% while the Mn concentration was equal to 5.5% in GaMnAs single layers and 6% in the magnetic layers of superlattice structures.Visit www.three-fives.com for the latest advanced semiconductor industry news     

Ferromagnetism of low-dimensional structures based on III-Mn-V semiconductors in the vicinity of the insulator-to-metal transition

The structural and transport properties of the GaAs/Mn/GaAs/In _x Ga_{1 − x} As/GaAs quantum wells (QWs) with the Mn layer distant from the QW and the Mn content ranging from 4 to 10% that correspond to the reentrant metal-to-insulator transition observed in the bulk GaMnAs are studied. The X-ray diffractometry and reflectometry are used to reconstruct the distribution profile of the Mn layers and to demonstrate the absence of the Mn atoms in the QW volume. The mobility of holes in the objects under study is greater than the known mobilities for the GaMnAs magnetic heterostructures by more than two orders of magnitude, which makes it possible to observe the Shubnikov-de Haas oscillations, proving the 2D character of the hole energy spectrum. A significant role of the 2D holes in the ferromagnetic ordering of the Mn layer is demonstrated under such conditions. The supporting evidence results from the observation of a maximum on the curves of the resistance versus temperature (at 25–40 K), whose position is in agreement with the calculated Curie temperature for the structures with indirect exchange interaction via the 2D-hole channel and the observation of the negative spin-dependent magnetoresistance (NM) and the anomalous Hall effect (AHE) that correlates with the theoretically calculated results for the ferromagnetic 2D III-Mn-V systems. The features of the NM and AHE revealed in the structures with the dielectric conduction indicate the effects of phase separation lying in the fragmentation of the sample into mesoscopic ferromagnetic domains separated by tunnel transparent paramagnetic layers. Such NM and AHE features are also observed in the weakly dielectric InMnAs films, which points to an important role of such effects in the III-Mn-V systems in the vicinity of the insulator-to-metal transition.     

MBE生长的Al_xGa_(1-x)As合金的光学分析(英文)

Presented here are a combined Rayleigh, Raman and photolumines-cence studies of AlxGa1-xAs alloy grown by molecular-beam-epitaxy. The Rayleigh intensity is found to be sensitive to the degree of disorder in the alloy. The appearance of "forbidden" TO mode in Raman spectra is likely due to twinning effects inducing internal microscopic misorientation. All LO phonons, around X and L points, contribute to the phonon-assisted exciton recombination process examined in photoluminescence spectra. Also shown in the paper is the discrepancy between the results of existing methods to determine alloy concentration from Raman and photoluminescence data.     

激光与外载荷联合加载7075铝合金的实验研究

为了研究7075铝合金在激光与外载荷联合加载下的失效行为, 采用最大拉力50 kN的拉伸伺服试验机与工作波长为1070 nm的6 kW连续光纤激光系统对7075铝合金进行了不同预载荷与不同激光功率密度下的联合加载实验, 获得了该材料的拉应力-时间曲线、温度-时间曲线、失效时间-功率密度曲线、失效温度-功率密度曲线等, 分析了功率密度与预载荷对失效过程、失效温度和断裂形貌的影响。结果表明, 在相同的预载荷下, 激光功率密度的增大会导致失效时间非线性下降, 失效温度是否有较大变化取决于预载荷的大小, 当预载荷大(330 MPa, 440 MPa)时, 失效温度随功率密度增加略有升高, 预载荷较小(110 MPa, 220 MPa)时, 失效温度变化规律不单调; 在相同的激光功率密度下, 预载荷增大, 失效时间减少, 功率密度较大、预载荷较小时, 失效行为变得相似; 在一定的功率密度(315 W/cm2, 351 W/cm2)下, 失效温度随预载荷的增大先增大后减小。该结果进一步揭示了7075铝合金的失效机理。     

Growth and Raman Scattering Investigation of a New 2D MOX Material: YbOCl

MOX (M = Fe, Co, Mn, Cr, Lanthanide, or Actinide metals; O = oxygen, X = F, Cl, Br, I), an emerging type of 2D layered materials, have been theoretically predicted to possess unique electronic and magnetic properties. However, 2D MOX have rarely been investigated. Herein, for the first time, ultrathin high‐quality ytterbium oxychloride (YbOCl) single crystals are successfully synthesized via an atmospheric pressure chemical vapor deposition method. Both theoretical simulations and experimental measurements are utilized to systematically investigate the Raman properties of 2D YbOCl nanosheets. The experimentally observed E_g mode at 85.53 cm^?1 and A_1g mode at 138.17 cm^?1 demonstrate a good match to the results from density functional theory calculations. Furthermore, the temperature‐dependent and thickness‐dependent Raman scattering spectra reveal the adjacent layers in YbOCl nanosheets show a relatively weak van der Waals interaction. Additionally, the polarized‐dependent Raman scattering spectra show the intensity of A_1g mode exhibits twofold patterns while the intensity of the E_g mode remains constant as the rotation angle changes. These findings could provide the first‐hand experimental information about the 2D YbOCl crystals.     

在亚音速气流作用下连续激光辐照铝合金的穿孔效应

不同气流速度作用下激光辐照靶材的穿孔效应不同。实验研究了亚音速气流（0~0.7 Ma）环境下,1 070 nm连续激光辐照7075铝合金的穿孔效应。对铝合金中心点温度历史、穿孔时间、穿孔孔径以及表面形貌变化进行了分析,结果表明:在相同气流速度下,随着入射激光功率密度的增加,铝合金表面温升速度加快且最终熔融层所达到的平衡温度增大;铝合金的穿孔时间呈指数减小;孔径增大速率呈指数减小。在相同激光功率密度下,随着气流速度的增加,铝合金穿孔时间总体呈先增大后减小至平稳之后再增大的趋势;熔融物移除速度和气流的冷却作用这两方面共同导致在0.1 Ma附近出现最长穿孔时间,在0.3 Ma附近出现最短穿孔时间,0.6 Ma的穿孔时间与0 Ma的穿孔时间大致相等在5.5 s左右;随着气流速度增大冷却效应增强,在0.7 Ma之后铝合金并未出现穿孔。对流冷却导致熔融物快速冷凝,被移除的熔融物集中在气流的下游区域。     

强脉冲激光照射TC11合金组织和抗氧化性能分析

为了改善TC11钛合金表面性能,采用强激光照射方法对其进行表面辐照处理,并研究脉冲能量密度对激光照射TC11钛合金表面形貌及性能的影响。结果表明,经过1J/cm2的强脉冲激光照射后,合金表面出现熔融,随着脉冲能量密度增大,合金表层的熔坑外径变大;激光照射后合金表层形成了约1.5μm外径的微孔,其构成元素主要为Mg,O,S,C;经脉冲照射处理后TC11合金显微硬度明显增大;当脉冲能量密度增加后,合金显微硬度也随之上升,合金试样的抗高温氧化性能得到明显的提升;合金表层形成的氧化物包含颗粒状和层状两种形貌类型,氧化物主要由Al₂O₃与Cr₂O₃构成。该研究对提高TC11钛合金表面抗氧化性能是有帮助的。     

GaNAs的声子拉曼散射研究

对分子束外延生长的GaNAs外延层进行了拉曼散射研究,观测到了由于导带中的E＋态所引起的共振散射和由此产生的布里渊区非Г点声子的拉曼峰,清晰地观测到了随氮含量增大,氮在GaAs中的局域模振动演变为GaNAs中的类GaN晶格声子带模。通过样品在850度快速热退火前后拉曼谱的对比,推测地指认了两个与氮的成对或成团效应有关的振动峰。