Selective area growth of III–V compound semiconductors by chemical beam epitaxy

The reactions of triethylgallium (TEG) on a silicon nitride surface have been investigated to determine the underlying causes for selective area epitaxy. Using the techniques of X-ray photo electron spectroscopy and temperature programmed desorption, TEG is found to weakly adsorb on defect sites at room temperature. Desorption is favoured over further decomposition at higher substrate temperatures. The results are compared with the interaction of TEG on GaAs(100) surface and the implications for the influence of surface arsenic on selective area growth are discussed.     

Annealing effects on electrical, optical and structural properties of semiconducting transparent tetra-tert-butyl 2,3 naphthalocyanine thinfilms

Although there are lot of early reports on inorganic semiconducting transparent thinfilms, very few experimental results have been reported regarding the organic semiconducting transparent thinfilms especially in the area of Naphthalocyanines. Here we report on the preparation and characterization of transparent and semiconducting 2,11,20,29 Tetra Tert-Butyl 2,3 Naphthalocyanine (TTBNc) thinfilms using Physical Vapor Deposition Technique. Post deposition air and vacuum annealing is done on thinfilms. From the DC electrical conductivity studies, the activation energy has been calculated using the Arrhenius plot and the bandgap energy has been obtained from the optical transmission spectra. The different structural parameters like crystal structure; grain size and surface morphology are measured from the x-ray diffraction (XRD) and scanning electron microscopic analysis (SEM) respectively. Atomic force microscopic (AFM) images of different TTBNc thinfilms account for significant changes on surface level patterns and a clear evidence of agglomeration of nano crystalline materials. Further the average grain size is calculated and confirmed in the nano level at which it forms clusters to get the particular surface topology.     

The role of dislocations in the formation of mechanical stresses during annealing of gallium arsenide single crystals

The effect of dislocations on the change of mechanical stresses in undoped semi-insulating gallium arsenide single crystals has been studied during their annealing in vacuum and in the arsenic atmosphere. The phenomena observed are explained by the effect of dislocations playing the role of channels for arsenic diffusion on the concentration of intrinsic point defects in the crystal regions surrounding dislocations. The mechanism of arsenic diffusion over dislocations allows one to consider dislocations as sources and sinks of arsenic without the translational and twinning processes and, thus, makes the well-known data on the reactions of dislocation interaction with point defects and the experimental structural data for single crystals more consistent.     

Theoretical analysis of abnormal grain growth in HCP-polycrystalline thin films on rigid substrates

In this paper, the effects of grain orientation on preferred abnormal grain growth in HCP-polycrystalline thin films have been analysed with respect to strain energy. The calculated results showed that C_hkl, the average values of the orientation factor, decreased with increase of 1 for the same h and k and increased with increase of h or/and k for constant 1. Where (hkl) denoted a particular grain orientation, that is, the grains with (hkl) planes oriented parallel to the film surface. This is preannounced that, considering the strain energy solely, the grains with higher 1 and lower h and k should be favorable in HCP-polycrystalline thin films on rigid substrates after annealing.     

X-ray triple-crystal diffractometer investigation of arsenic implanted silicon after pulsed laser irradiation

X-ray triple-crystal diffractometry (TCD) of parallel (+n, -n, +n) setting was used to investigate the structural changes of silicon surface layers after arsenic implantation and pulsed laser irradiation. The implated layers of different doses show enlarged lattice constants in the disturbed crystalline parts. After low energy annealing a polycrystalline surface layer is built up from the amorphous layer while the crystalline layer below it is not significantly changed. High energy annealed regions show recrystallisation with high degree of perfection and decreased lattice constant. The results of TCD measurements are compared with results of double-crystal diffractometer investigations and advantages of the TCD method are discussed.     

氩气退火时间对Fe(Se,Te)薄膜的性能影响研究

作为一种铁基超导薄膜,Fe(Se,Te)薄膜具有晶体结构简单、所包含的元素较少、易于合成的特点,不仅有利于超导机理研究而且有着潜在的技术应用价值。本文通过磁控溅射在温度为320 ℃的CaF₂单晶衬底上制备了Fe(Se,Te)薄膜,并在氩气氛围下进行了退火处理。研究了退火时间对Fe(Se,Te)薄膜的晶体结构、微观形貌、成分组成以及电输运特性的影响。结果表明:Fe(Se,Te)薄膜的结晶性较好,退火有助于消除薄膜样品中的FeSe相,薄膜的晶格常数c对退火不敏感,退火后薄膜晶粒尺寸变大;Fe(Se,Te)薄膜成分与靶材的名义组分存在一定的偏差,退火时间越长,Fe(Se,Te)薄膜表面的颗粒越密集;Fe(Se,Te)薄膜的电阻随温度升高而减小,呈现出半导体特性,退火3 h后电阻明显增大。     

不同退火温度对钡铁氧体薄膜磁性的影响

M型钡铁氧体(BaFe₁₂O₁₉, BaM)是一种单轴磁晶各向异性的六角晶系硬磁材料,由于其具有很强的各向异性场,因此在自偏置微波器件领域具有广阔的应用前景。本文采用常温射频磁控溅射法在(000l)取向的蓝宝石衬底上沉积了厚度约为130 nm的BaFe₁₂O₁₉非晶薄膜,然后分别在850 ℃、900 ℃、950 ℃、1 000 ℃对其空气退火处理3 h,得到BaM晶体薄膜样品。采用X射线衍射仪对薄膜样品进行物相及晶体生长取向鉴别,采用扫描探针显微镜和扫描电子显微镜对薄膜样品的粗糙度和表面形貌进行测量和观察,采用振动样品磁强计对样品进行了静态磁性能测试。实验结果表明,退火后的薄膜样品的主晶相为BaM,且具有(000l)取向择优生长,其微观组织结构都表现为C轴垂直于膜面的颗粒状结构。退火温度为900 ℃时所得样品的各项性能达到最佳,其表面粗糙度为2.8 nm,矩形比为0.84,饱和磁化强度为247 emu/cm³,矫顽力为1 528 Oe。     

Role of the substrate deoxidation process in the growth of strained InAs/InP heterostructures

We have investigated the role of the arsenic flux used during the substrate deoxidation process in the MBE (molecular beam epitaxy) growth of strained InAs/InP heterostructures. Two different experiments were performed: (i) thermal cleaning of the InP wafer under an As flux at different exposure times and (ii) the growth of very thin InAs layers (3-9 ML). The samples grown were characterized by Raman spectroscopy and selected area X-ray photoelectron spectroscopy. The results obtained demonstrated the formation of an InAs_xP_1−x sublayer at the interface of the InAs/InP system. The annealing of InP under an As flux promotes not only As → P substitution on the surface, but also the subsequent diffusion of As atoms into the deeper subsurface region of InP.     

Temperature dependence of grain growth in zone-refined tin containing large additions of zinc in solid solution

Grain growth in zone-refined tin containing high concentrations > 0.05 < 0.40 wt% Zn in solid solution have been investigated in the temperature range 70–160°C. It has been found that increasing the zinc content by a factor of 8 decreased the rate of grain growth by ∼ 30% at all annealing temperatures, and this was attributed to small variations of grain boundary mobility. In addition, the increase of annealing temperature from 70 to 160°C resulted in the increase of grain growth by a factor of ∼ 50 at any given concentration, which shows that the rate of grain growth is not strongly influenced by increasing the zinc concentration. The energy activating the growth process was calculated for all concentrations investigated and had a nearly constant value of ∼ 1 eV. An empirical formula was proposed relating the rate of grain growth and the solute concentration.     

不同退火条件对PEALD制备的Ga2O3薄膜特性的影响

利用等离子增强原子层沉积技术(PEALD)在c面蓝宝石衬底上制备了氧化镓(Ga₂O₃)薄膜,研究了退火气氛(v(N₂)∶v(O₂)=1∶1(体积比)、空气和N₂)及退火时间对Ga₂O₃薄膜晶体结构、表面形貌和光学性质的影响。研究结果表明,退火前的氧化镓处于亚稳态,不同退火气氛下退火后晶体结构发生明显改变,而且退火气氛中N₂比例增加有利于Ga₂O₃重结晶。在N₂气氛下退火达到30 min,薄膜结构已由亚稳态转变成择优取向的β-Ga₂O₃。而且表面形貌分析表明,退火30 min后表面形貌开始趋于稳定,表面晶粒密度不再增加。另外实验样品在 400~800 nm的平均透射率几乎是100%,且光吸收边陡峭。采用N₂气氛退火,对于富氧环境下沉积的Ga₂O₃更利于薄膜表面原子迁移,以及择优取向Ga₂O₃重结晶。     

The behaviour of copper on gallium arsenide

Cu has been reported to diffuse rapidly in GaAs at low temperatures (2.3×10^-5 cm² s^-1 at 600°C). The rapid diffusion is attributed to the interstitial movement of Cu atoms. The present investigation was undertaken to examine preferential diffusion of Cu⁺ along dislocations and grain boundaries in GaAs. The experiments consisted of depositing ⁶⁴Cu on a GaAs water surface, annealing in vacuum, and observing the Cu distribution by autoradiography. From these observations no preferential diffusion along dislocations or grain boundaries was detected in SI GaAs annealed between 600 and 1000°C. In the sample annealed above 800°C, the deposited Cu reacted with the GaAs forming a liquid on the sample surface, which solidified into complex Cu-Ga-As compounds. The liquid also produced Cu-rich pipes which extended through the GaAs wafer.     

Compositional mapping of GaSb wafers from as-grown crystals and after post-growth annealing treatments

Spatial compositional analysis has been carried out on single and polycrystal wafers of GaSb grown from stoichiometric and non-stoichiometric melts. In crystals grown from stoichiometric melt, the ratio of Ga to Sb is slightly more and remains uniform throughout. At the grain boundaries in polycrystals, the Sb content is more than in the other regions of the crystal. Crystals grown from either Ga- or Sb-rich melts exhibit inclusions of the excess component. Post-growth annealing treatments in vacuum and Ga-rich atmospheres have been performed. Heat treatments in vacuum atmosphere produce very little effect on the local composition of the crystal. On the other hand, localized crystallization at grain boundaries and inclusions takes place in the presence of excess gallium. It has been shown that annealing treatments in Ga ambient can produce defect-free wafers with extremely homogeneous composition. It is concluded that the excess Sb which is liberated from the crystal during growth resides at the grain boundaries and other extended defect centers. The vacant Sb sites are then responsible for the formation of the native acceptor centers like V_Ga and Ga_Sb.     

Polycrystalline LaFe3CoSb12 material manufactured by melt-freeze-annealing method

A new method called melt-freeze-annealing has been developed to fabricate polycrystalline thermoelectric LaFe₃CoSb₁₂ The melting and annealing temperatures as well as the freezing style all can affect the phase content, porosity and grain size of skutterudite polycrystalline materials. The use of a higher melting temperature and a appropriate buffer temperature with annealing at about 700°C are the best conditions for fabricating the LaFe₃CoSb₁₂ polycrystalline materials. The polycrystalline skutterudite materials fabricated by a melt-freeze-annealing procedure possessed high skutterudute content, fine grain size and very low porosity, and are suitable for thermoelectric usage.     

单晶硅外延生长晶化硅薄膜的研究

采用P型单晶硅片为衬底,并经混合酸溶液腐蚀抛光、清洗后,利用射频磁控溅射镀膜系统在其表面制备非晶硅薄膜;再结合快速光热退火工艺,于N2气氛下480℃退火30 min,得到晶化硅薄膜;利用光学金相显微镜、XRD衍射仪和拉曼散射光谱(Raman)仪对单晶硅衬底和晶化硅薄膜进行结构和性能表征.研究了混合酸溶液对单晶硅表面腐蚀效果、籽晶诱导外延生长晶化硅薄膜的物相结构和薄膜带隙.结果表明:采用混合酸溶液腐蚀后得到表面平整、光滑的单晶硅衬底;非晶硅薄膜经过快速退火后受籽晶诱导生成晶化硅薄膜,其晶相沿单晶硅衬底取向择优生长;随着非晶硅薄膜厚度从80 nm增加到280 nm,晶化后硅薄膜的表面粗糙度逐渐减小,晶化率从90.0;逐渐降低到37.0;;晶粒尺寸从6.65 nm逐渐减小到1.71 nm;带隙从1.18 eV逐渐升高到1.52 eV.     

Surface reconstructions and growth mode transitions of AlAs(100)

The surface reconstructions of AlAs(100) layers grown by molecular beam epitaxy (MBE) on GaAs(100) were mapped as a function of substrate temperature and arsenic flux. Three main reconstructions were observed - a c(4×4) at lower temperatures and higher arsenic fluxes, a (2×4) at middle temperatures, and a (3×2) at higher temperatures and lower arsenic fluxes. Growth of AlAs on AlAs(100) is layer-by-layer for the high temperature and low temperature reconstructions. In the mid-temperature region, AlAs grows rough on (2×4) reconstructed AlAs(100) as indicated by rapidly damped reflection high-energy electron diffraction (RHEED) intensity oscillations and the appearance of three-dimensional (3D) features. The addition of fractional layers of Ga enhances the smooth growth of AlAs. A metastable (5×2) reconstruction was observed when a fraction of a layer of Ga was present on the surface. The results indicate that Ga segregates during the growth of AlAs on GaAs(100) at temperatures at least as low as 500°C, and that annealing at temperatures above 700°C removes most of the Ga from the surface.     

4,2 K-Photoluminescence Study of the Annealing Process in Neutron-irradiated Silicon

Described are experimental results of impurity characterisation and defect kinetic studies aimed at investigating annealing processes in neutron-irradiated silicon. In addition to Hall effect and resistivity measurements, low-temperature luminescence spectroscopy has been made use of for the physical characterisation, making it possible to determine shallow impurities and observe their kinetic during annealing, especially with respect to phosphorus activation, along with the changes in the electrical properties.     

Investigation of defects in low-temperature-grown GaAs using optical transient spectroscopy

Optical transient current spectroscopy (OTCS) has been used to investigate defects in the low-temperature-grown GaAs after postgrowth rapid thermal annealing (RTA). Two samples A and B were grown at 220°C and 360°C on (0 0 1) GaAs substrates, respectively. After growth, samples were subjected to 30 s RTA in the range of 500–800°C. Before annealing, X-ray diffraction measurements show that the concentrations of the excess arsenic for samples A and B are 2.5×10¹⁹ and 1×10¹⁹ cm⁻³, respectively. It is found that there are strong negative decay signals in the optical transient current (OTC) for the annealed sample A. Due to the influence of OTC strong negative decay signals, it is impossible to identify deep levels clearly from OTCS. For a comparison, three deep levels can be identified for sample B before annealing. They are two shallower deep levels and the so-called As_Ga antisite defect. At the annealing temperature of 600°C, there are still three deep levels. However, their structures are different from those in the as-grown sample. OTC strong negative decay signals are also observed for the annealed sample B. It is argued that OTC negative decay signals are related to arsenic clusters.     

电化学共沉积法制备GaAs纳米结构薄膜及表征

以含一定比例Ga与As2O3的酸性溶液(pH=2.5)作为前驱溶液,以Pt片为对电极,饱和甘汞电极(SCE)为参比电极,室温下利用三电极电化学站在Ti衬底上恒压沉积GaAs薄膜.然后对GaAs薄膜进行退火处理.利用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM),以及荧光光度计(PL)分别对不同沉积电压下所制备的薄膜的晶体结构,薄膜形貌以及光学性能进行分析表征.结果表明:沉积电压以及退火过程对GaAs薄膜的形貌、晶体结构、薄膜质量有很大影响,所制备的GaAs薄膜退火前晶化程度较低,部分粒子表现出不均匀团聚.光致发光峰为红光发射,且单色性好.退火后的GaAs薄膜为面心立方晶型,呈纳米颗粒状,薄膜的光电性能明显提高.     

Magnetic behavior and microstructure of Finemet-type ribbons in both,surface and bulk

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co- and Ni-rich amorphous ferromagnetic (Finemet) ribbons using diverse procedures like the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements have evidenced the anisotropy of the treated samples. The main goal of this work has been the structural and microstructural analysis of the treated ribbons using X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallization of the surface without evidences of amorphous matrix, which contrast with XRD measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behavior that is expected for the surface of the ribbons, measuring surface hysteresis loops that show much higher coercive field values than in the bulk.     

Influence of surface treatments on crystalline germanium heterojunction solar cell characteristics

Hydrogenated amorphous Si (a-Si:H) has been applied to crystalline germanium (c-Ge) heterojunction solar cells and the influence of the surface treatments applied before a-Si:H deposition process has been studied. We found that PH₃ exposure treatment after surface oxide removal by annealing is effective to improve c-Ge heterojunction solar cell performance. The conversion efficiency of the c-Ge heterojunction solar cell applied PH₃ exposure treatment was up to 5.29% and the solar cell had better temperature coefficient than the c-Ge homojunction solar cell. These results suggest that the c-Ge substrate surface after oxide removal by annealing is covered with negatively charged dangling bonds, and the phosphorus adsorbed onto the c-Ge surface provides electron as a donor and corrects the band bending induced by negatively charged dangling bonds.