RHEED monitoring of elastic stresses during MBE growth of group III nitride heterostructures

Results of statistical analysis of the patterns of reflection high-energy electron diffraction (RHEED) measured during molecular beam epitaxy (MBE) of heterostructures of wide-bandgap (Al, Ga, In)N compounds are presented, which can be used for determining the lateral lattice constant (a) of the epitaxial layers. It is established that the error of determination can vary from a minimum of 0.17% up to several percent, depending on the contrast of RHEED patterns, which is determined by the stoichiometry of MBE growth. It is demonstrated that the RHEED data can reveal relaxation of elastic stresses during the growth of short-period {GaN(4 nm)/AlN(6nm)}₃₀/AlN superlattices.     

The growth of high quality GaMnAs films by MBE

Using As₂ as an arsenic source together with other appropriate growth and annealing procedures, we have improved the electrical and magnetic properties of GaMnAs films and obtained Curie temperatures as high as 159 K. For Mn concentrations up to 7%, we have demonstrated that the compensation previously observed in such films is mainly due to Mn interstitials, which can be removed by using appropriate annealing procedures for thin films. For the Mn concentrations >7%, we suggest that additional As_Ga defects also cause compensation, which cannot be removed by our present annealing procedure.     

The growth of high quality GaMnAs films by MBE

Using As₂ as an arsenic source together with other appropriate growth and annealing procedures, we have improved the electrical and magnetic properties of GaMnAs films and obtained Curie temperatures as high as 159 K. For Mn concentrations up to 7%, we have demonstrated that the compensation previously observed in such films is mainly due to Mn interstitials, which can be removed by using appropriate annealing procedures for thin films. For the Mn concentrations >7%, we suggest that additional As_Ga defects also cause compensation, which cannot be removed by our present annealing procedure.     

缓冲层对氮化镓二维生长的影响

报道了在射频等离子体（RF-Plasma)辅助的分子束外延（MBE）技术中，使用白宝石（0001）衬底，采用低温缓冲层工艺外延氮化镓（GaN)。通过原子力显微镜（AFM）的表面形貌比较及X射线双晶衍射（XRD）ω扫描摇摆曲线的分析，讨论了低温缓冲层成核机理及缓冲层生长温度与形成准二维生长的关系，确立了缓冲层的三维成核，准二维生长的生长机理，并在此基础上实现了氮化镓外延层更好地二维生长，进一步提高了氮化镓外延层的晶体质量。     

InGaAs/GaAs异质薄膜的MBE生长研究

利用分子束外延技术,在GaAs(001)基片上外延InGaAs/GaAs异质薄膜,通过RHEED图像演变实时监控薄膜生长状况,采用RHEED强度振荡测量薄膜生长速率,确定薄膜中In/Ga的组分比,并提出控制InGaAs薄膜中In/Ga组分比的生长方法.根据RHEED图像,指出获得的InGaAs薄膜处于(2×3)表面重构...     

The status and future development of innovative optoelectronic devices based on III-nitrides on SiC and on III-antimonides

High-brightness nitride-based LEDs have been grown on SiC substrates, which offers many advantages in the production both from epitaxial, chip and device processing point of view. Optimized InGaN/GaN/GaAlN MQW structures and improved chip and package designs were developed, resulting in optical outputs that exceed 7 mW at 20 mA in a 5 mm axial lamp. InGaN oxide stripe lasers (450 μm×3.5 μm) with an emission wavelength around 420 nm were fabricated showing threshold currents of 330 mA and turn-on voltages of about 21V operated under pulse current injections at room temperature. Strained layer GaInAsSb/AlGaAsSb quantum well lasers operating near room temperature with emission wavelengths up to 2.26 μm and a cw output of 240 mW were demonstrated. Short-period InAs/GaInSb superlattices with different InAs layer widths have been used for the fabrication of photodiodes, showing responsivity spectra with cut-off wavelengths of 4.5 and 10 μm, respectively.     

MBE growth of 5 μm quantum cascade lasers

We have demonstrated quantum cascade lasers (QCL) emitting at ∼5μm based on efficient injection of the four quantum wells active region design with vertical transitions and strain-compensated superlattice with high injection efficiency and short ground state lifetime. Using a processing sequence adjusted for QCL state of the art devices were reproducibly obtained.     

MBE生长GaAs(001)薄膜表面的Ostwald熟化过程研究

采用带有RHEED的MBE技术,利用RHEED图像演变实时监控薄膜生长状况,通过RHEED强度振荡测算薄膜生长速率,在GaAs(001)基片上同质外延GaAs薄膜。利用STM对MBE生长的GaAs薄膜表面的熟化过程进行了深入研究。研究发现,随着退火时间的延长,刚完成生长的GaAs表面从具有大量岛和坑的粗糙表面逐渐熟化,在熟化过程中岛不断合并扩大并与平台结合,而坑却逐渐消失。指出当熟化过程完成后GaAs表面将进入原子级平坦状态,并详细解释了熟化过程GaAs表面各种形貌特征形成的内在原因。     

Integrated analytical equipment for control of film growth in MBE technology

The integrated analytical equipment has been developed for in-situ measuring growth rate and film composition by the ultra-fast ellipsometer, surface temperature by the polarization-type pyrometer and for precise control over the epitaxial processes by automatic control system. This complex was used to control the mercury cadmium telluride heteroepitaxial structure growth on GaAs substrate with various composition distributions throughout the thickness. The maintenance accuracy of Hg_1−xCd_xTe composition during growth was up to ΔX_CdTe=±0.0005. The maintenance accuracy of substrate temperature was found to be up to ±1°C.     

Influence of the luminous gas phase on direct current plasma polymerized hydrocarbon film growth

The characteristics of the glow created in plasma polymerization systems are notably different from inert gas plasmas such as argon, in which the well-known negative glow is the primary glow. The study of direct current (DC) glow discharges of a series of saturated hydrocarbon monomers indicated that cathode glow forms the distinctive glow in plasma polymerization systems. It forms a strong contrast to characteristic negative ionization glow of glow discharges of inert gases that do not polymerize. Optical emission analysis results obtained from these plasma deposition systems indicated that polymerizable species are mainly formed in cathode glow region. The growth of direct current plasma polymerized hydrocarbon film clearly showed the dominating effects of luminous gas phases on the polymerizable tendency in plasma polymerization system.     

微型热管技术的研究现状与发展

微型热管（micro heat pipe，MHP）被广泛用于冷却航天、航空、军用武器、车辆、计算机等众多领域的电子设备，是有效冷却高热流密度电子器件的主要途径之一，已成为现代热管技术重要的发展方向和研究热点。目前对MHP的研究主要集中在管内流动及传热、传质的机制研究，新型高效结构形式的设计，制造工艺技术的改进等方面。较系统地总结近来MHP在理论、设计及制造工艺等方面的技术研究进展，综述其应用现状并分析其发展趋势。     

国内检测实验室的现状与发展趋势

本文阐述了国际与国内第三方检测机构(实验室)现状,分析了当前国内第三方检测机构(实验室)存在的问题,提出了有针对性的解决方法,并对该行业的发展趋势做了合理的分析与指引,使国内第三方检测机构(实验室)更有目标性及更加规范化地健康发展。     

Selective-area catalyst-free MBE growth of GaN nanowires using a patterned oxide layer

GaN nanowires (NWs) were grown selectively in holes of a patterned silicon oxide mask, by rf-plasma-assisted molecular beam epitaxy (PAMBE), without any metal catalyst. The oxide was deposited on a thin AlN buffer layer previously grown on a Si(111) substrate. Regular arrays of holes in the oxide layer were obtained using standard e-beam lithography. The selectivity of growth has been studied varying the substrate temperature, gallium beam equivalent pressure and patterning layout. Adjusting the growth parameters, GaN NWs can be selectively grown in the holes of the patterned oxide with complete suppression of the parasitic growth in between the holes. The occupation probability of a hole with a single or multiple NWs depends strongly on its diameter. The selectively grown GaN NWs have one common crystallographic orientation with respect to the Si(111) substrate via the AlN buffer layer, as proven by x-ray diffraction (XRD) measurements. Based on the experimental data, we present a schematic model of the GaN NW formation in which a GaN pedestal is initially grown in the hole.     

The status and evolution of plasma Wakefield particle accelerators

The status and evolution of the electron beam-driven Plasma Wakefield Acceleration scheme is described. In particular, the effects of the radial electric field of the wake on the drive beam such as multiple envelope oscillations, hosing instability and emission of betatron radiation are described. Using ultra-short electron bunches, high-density plasmas can be produced by field ionization by the electric field of the bunch itself. Wakes excited in such plasmas have accelerated electrons in the back of the drive beam to greater that 4 G eV in just 10 cm in experiments carried out at the Stanford Linear Accelerator Centre.     

The effects of load ratio on environmentally assisted fatigue crack growth

A modification to the model of Weir et al. for surface reaction and transport controlled fatigue crack growth has been developed to explicitly account for the effect of load ratio on environmentally assisted fatigue crack growth. Load ratio was found to affect principally gas transport to the crack tip, and therefore affected only transport controlled crack growth response. Experimental verification of the modified model was made by studying the room temperature fatigue crack growth responses at different load ratios for a 2219-T851 aluminum alloy exposed to water vapor.The results show that the effects of load ratio can be attributed to two different sources—one relating to its effect on local deformation at the crack tip and is reflected through the mechanical component, (d$\text{a}$/d$\text{N}$)₀ and the other on its role in modifying environmental effect and is manifested through the corrosion fatigue component, $\text{(da/dN)}{}_{\mathrm{cf}}$ Furthermore, the results show that the saturation value of corrosion fatigue component, $\text{(da/dN)}{}_{\mathrm{cf,s}}$, is essentially independent of $\text{R}$, and that the exposure needed to produce “saturation response” ($\text{P}{}_0\text{/2f)}{}_{\mathrm{s}}$, as a function of load ratio can be predicted from the modified model. The modified model, therefore, allows one to predict the corrosion fatigue crack growth response for any load ratio on the basis of measurements made at a single load ratio, provided that the values of ($\text{da/dN}$), are known.     

直流热阴极PCVD法间歇生长模式制备金刚石膜

采用直流热阴极PCVD(Plasma chemical vapor deposition)法间歇生长模式制备金刚石膜,通过加入周期性的刻蚀阶段清除金刚石膜在一定生长期中形成的石墨和非晶碳等杂质,实现了金刚石膜生长的质量调控。间歇式生长过程分为沉积阶段和刻蚀阶段,两个阶段交替进行。采用Raman光谱、SEM和XRD对所制金刚石膜的品质进行了表征,并与同样生长条件下连续生长模式制备的金刚石膜样品进行了比较。结果表明,当单个生长周期为30 min(沉积时间为20 min、刻蚀时间为10 min)时,直流热阴极PCVD法间歇生长模式制备的金刚石膜中的非金刚石相杂质含量低于连续间歇生长模式制备的金刚石膜。     

质子交换膜的研究现状与进展

简述了质子交换膜燃料电池中质子交换膜的质子传导机理;讨论了目前质子交换膜存在的甲醇渗透、耐温性等共性问题,就如何解决这些问题进行了评述,同时,论述了质子交换膜的研究开发现状及其发展前景。     

RHEED实时监控下MBE生长不同In组分的InGaAs薄膜

利用分子束外延技术,通过RHEED图像演变实时监控薄膜生长状况,采用RHEED强度振荡测量薄膜生长速率,固定Ga源温度、改变In源温度在GaAs（001）基片上外延生长了不同In组分（39%、29%、19%）的InGaAs薄膜。比较RHEED强度振荡以及RHEED衍射图像,发现随着In组分的增加In-GaAs的生长将很快进入三维粗糙表面生长模式,并指出In0.19Ga0.81As和In0.29Ga0.71As薄膜处于（2×3）表面重构相。In0.19Ga0.81As样品进行退火处理后完成STM扫描分析,证实样品为表面原子级平整的In-GaAs薄膜。     

Peculiarities of the MBE growth of nanowhiskers on GaAs(100) substrates

We have studied the formation of nanowhiskers (NWs) by molecular beam epitaxy (MBE) on GaAs(100) substrates. The MBE growth of NWs exhibits two stages (initial and developed) and leads to the formation of NWs with surface morphology of two types (nucleation and intergrowth). The stage of developed growth is characterized by the predominant formation of intergrown NWs oriented in the 〈111〉B direction, having (110) habit (including the NW tip surface) and hexagonal cross sections with a transverse size within 50–300 nm. It was found that the transverse size of a hexagonal NW may significantly differ from that of an Au-GaAs melt droplet. The ratio of longitudinal and transverse dimensions of intergrown NWs can be on the order of 150 and above. When the transverse size of NWs exceeds a certain value (about 200 nm), the crystal length exhibits a slight decrease. The existence of two types of morphology is indicative of inhomogeneous character of the NW growth on a GaAs(100) surface, which depends on the catalyst droplet size, effective thickness of the deposited GaAs layer, and the growth temperature.