Thermal stability of Mg2Si epitaxial film formed on Si（111） substrate by solid phase reaction

A single crystalline Mg2 Si film was formed by solid phase reaction(SPR) of a Si(111) substrate with an Mg overlayer capped with an oxide layer(s),which was enhanced by post annealing from room temperature to 100 ℃in a molecular beam epitaxy(MBE) system.The thermal stability of the Mg2 Si film was then systematically investigated by post annealing in an oxygen-radical ambient at 300℃,450℃ and 650 ℃,respectively.The Mg2 Si film stayed stable until the annealing temperature reached 450 ℃ then it transformed into amorphous MgO x attributed to the decomposition of Mg2 Si and the oxidization of dissociated Mg.     

Formation of nano-twinned 3C-SiC grains in Fe-implanted 6H-SiC after 1500-℃ annealing

A nano-twinned microstructure was found in amorphous SiC after high-temperature annealing. Grazing incidence x-ray diffraction, high-resolution transmission electron microscopy, and electron diffraction were performed to characterize the microstructure and phase transition in the recrystallization layer. After 1500 ℃ or 2-h annealing, 3C-SiC grains and numerous stacking faults on the {111} planes were visible. Some 3C-SiC grains have nano-twinned structure with {011} planes. Between the nano-twinned 3C-SiC grains, there is a stacking fault, indicating that the formation mechanisms of the nano-twinned structure are related to the disorder of Si atoms. The increase in the twin thickness with increasing annealing temperature demonstrates that the nano-twinned structure can sink for lattice defects, in order to improve the radiation tolerance of SiC.     

Effect of hydrogen introduced by channelling implantation on the microstructures in silicon wafers

High-resolution transmission electron microscopy has been employed to study the platelet defects before annealing and the extended defects generated by annealing in the channelling-implanted silicon wafers. It has been found that there apparently appear platelet defects of quite great size and spacing at the maximum projected range of ions (R _max). Additionally, the cracks induced by annealing at 550 °C are generated around R _max instead of the average projected range of ions (R _p) as it is in the non-channelling-implanted samples. Moreover, after annealing at 1000 °C, cracks without branches and cavities arranging in a single array, different from the forked cracks and cavities arranged in several arrays in the non-channelling-implanted samples, are observed in the channelling-implanted silicon wafers. It is suggested that those special microstructure characteristics are ascribed to the channelling effect of implanted hydrogen ions.     

Reaction between amorphous Si and crystalline Al in Al/Si and Si/Al bilayers: microstructural and thermodynamic analysis of layer exchange

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/Si and Si/Al bilayers was studied upon annealing at 250 °C by X-ray diffraction and Auger electron spectroscopy. The Al/a-Si bilayers and a-Si/Al bilayers were prepared by sputter deposition on single-crystal silicon wafers with a silicon-oxide film on top. During the isothermal annealing a layer-exchange process occurred in both types of bilayers. A continuous polycrystalline silicon (poly-Si) film was formed within, and thereby gradually replacing, the initial Al metal layer. The sublayer sequence in the original bilayer influenced the speed of the poly-Si formation and the layer-exchange process. After annealing, the Al fiber texture in the as-deposited bilayers had become stronger, the Al crystallites had grown laterally, and the macrostress in the Al layer had been released. The amorphous Si layer had crystallized into an aggregate of nanocrystals with {111} planes parallel to the surface, with a crystallite size of about 15–25 nm. An extensive analysis of the Gibbs energy change due to annealing showed that the layer exchange may be promoted by the release of elastic energy and grain growth for the Al phase. PACS 05.70.Jk; 61.43.Dq; 68.35.Rh; 61.72.Cc; 68.55.Jk     

Anisotropy of the mean free paths of phonons in single-crystal films of germanium,silicon, and diamond at low temperatures

The physical aspects of the influence of the elastic energy anisotropy of crystals on the anisotropy of the mean free paths of phonons in single-crystal films of germanium, silicon, and diamond in the diffuse scattering of phonons at the boundaries of the samples have been considered. It has been shown that, for sufficiently wide films of germanium, silicon, and diamond with the {100} and {111} orientations and the lengths of less than or equal to their width, the phonon mean free paths are isotropic (independent of the direction of the temperature gradient in the plane of the film). The anisotropy of the phonon mean free paths depends primarily on the orientation of the film plane and is determined by the focusing and defocusing of phonon modes. For single-crystal films of germanium, silicon, and diamond with the {100} and {111} orientations and lengths much larger than their width, the phonon mean free paths are anisotropic.     

Study of He-induced nano-cavities as sinks of oxygen for forming silicon-on-insulator

In the present work, a Cz-Silicon wafer is implanted with helium ions to produce a buried porous layer, and then thermally annealed in a dry oxygen atmosphere to make oxygen transport into the cavities. The formation of the buried oxide layer in the case of internal oxidation （ITOX） of the buried porous layer of cavities in the silicon sample is studied by positron beam annihilation （PBA）. The cavities are formed by 15 keV He implantation at a fluence of 2×10^16 cm^-2 and followed by thermal annealing at 673 K for 30 min in vacuum. The internal oxidation is carried out at temperatures ranging from 1073 to 1473 K for 2 h in a dry oxygen atmosphere. The layered structures evolved in the silicon are detected by using the PBA and the thicknesses of their layers and nature are also investigated. It is found that rather high temperatures must be chosen to establish a sufficient flux of oxygen into the cavity layer. On the other hand high temperatures lead to coarsening the cavities and removing the cavity layer finally.     

Secondary defects in low-energy As-implanted Si

14 /cm² dose of As ions followed by both isochronal and isothermal annealing. The elementary defects generated first during solid-phase epitaxial recovery of implantation-induced amorphous layers at temperatures of 550 °C and/or 600 °C are {311} defects 2–3 nm long. They are considered to be transformed into {111} and {100} defects after annealing at temperatures higher than 750 °C. These secondary defects show the opposite annealing behavior to the dissolution and growth by the difference of their depth positions at 800 °C. This phenomenon is explained by the diffusion of self-interstitials contained in defects. With regard to the formation and dissolution of defects, there is no significant difference between the effects of rapid thermal annealing (950 °C for 10 s) and furnace annealing (800 °C for 10 min). Received: 14 November 1997/Accepted: 16 November 1997     

Surface Structure of Large Synthetic Diamonds by High Temperature and High Pressure

With NiMnCo and FeCoNi alloys as solvent metals, large single-crystal diamonds of about 3mm across are grown by temperature gradient method （TGM） under high temperature and high pressure （HPHT）. Although both {100} and {111} surfaces are developed by a layer growth mechanism, some different characteristic patterns are seen clearly on the different surfaces, no matter whether NiMnCo or FeCoNi alloys are taken as the solvent metals. For {100} surface, it seems to have been melted or etched greatly, no dendritic patterns to be found, and only a large number of growth hillocks are dispersed net-likely; while for {111} surface, it often seems to be more smooth-faced, no etched or melted traces are present even when a lot of depressed trigonal growth layers. This distinct difference between {111} and {100} surfaces is considered to be related to the difference of surface-atom distribution of different surfaces, and {111} surfaces should be more difficult to be etched and more steady than {100} surfaces.     

A comparison of silicon oxide and nitride as host matrices on the photoluminescence from Er+ ions

This paper compares the properties of silicon oxide and nitride as host matrices for Er ions.Erbium-doped silicon nitride films were deposited by a plasma-enhanced chemical-vapour deposition system.After deposition,the films were implanted with Er3+ at different doses.Er-doped thermal grown silicon oxide films were prepared at the same time as references.Photoluminescence features of Er3+ were inspected systematically.It is found that silicon nitride films are suitable for high concentration doping and the thermal quenching effect is not severe.However,a very high annealing temperature up to 1200° C is needed to optically activate Er3+,which may be the main obstacle to impede the application of Er-doped silicon nitride.     

Blocking-Effekte bei Transmission von α-Teilchen durch Germanium- und Siliziumkristalle

The energy loss of channeled and blocked α-particles of ThC transmitted parallel to the {111} and also the {110} planes of germanium and silicon was investigated. In the spectrum of the transmittedα-particles measured with a small-acceptance-angle detector, in addition to the random and normally channeled α-groups a separated group with a high energy loss was observed in the direction of the {111} planes, while in the direction of the {110} planes this group is not well separated from the randomα-group. A model is proposed which describes this high energy loss for observation in the direction of either plane. In agreement with this model a higher yield ofα-particles with high energy loss in the {111} planes in comparison with the {110} planes of germanium and silicon was measured.     

Optical and electrical properties of BaSnO3 and In2O3 mixed transparent conductive films deposited by filtered cathodic vacuum arc technique at room temperature

For the crystalline temperature of BaSnO$_{3}$ (BTO) was above 650 ℃, the transparent conductive BTO-based films were always deposited above this temperature on epitaxy substrates by pulsed laser deposition or molecular beam epitaxy till now which limited there application in low temperature device process. In the article, the microstructure, optical and electrical of BTO and In$_{2}$O$_{3}$ mixed transparent conductive BaInSnO$_x$ (BITO) film deposited by filtered cathodic vacuum arc technique (FCVA) on glass substrate at room temperature were firstly reported. The BITO film with thickness of 300 nm had mainly In$_{2}$O$_{3}$ polycrystalline phase, and minor polycrystalline BTO phase with (001), (011), (111), (002), (222) crystal faces which were first deposited at room temperature on amorphous glass. The transmittance was 70%-80% in the visible light region with linear refractive index of 1.94 and extinction coefficient of 0.004 at 550-nm wavelength. The basic optical properties included the real and imaginary parts, high frequency dielectric constants, the absorption coefficient, the Urbach energy, the indirect and direct band gaps, the oscillator and dispersion energies, the static refractive index and dielectric constant, the average oscillator wavelength, oscillator length strength, the linear and the third-order nonlinear optical susceptibilities, and the nonlinear refractive index were all calculated. The film was the n-type conductor with sheet resistance of 704.7 $\Omega /\Box $, resistivity of 0.02 $\Omega \cdot$cm, mobility of 18.9 cm$^{2}$/V$\cdot$s, and carrier electron concentration of $1.6\times 10^{19}$ cm$^{-3}$ at room temperature. The results suggested that the BITO film deposited by FCVA had potential application in transparent conductive films-based low temperature device process.     

Thermally induced defect photoluminescence in hydrogenated amorphous silicon

The intrinsic defect photoluminescence of hydrogenated amorphous silicon (a-Si:H) films has been investigated at high intensities of optical pumping that lead to heating of the film. It has been revealed that, for short heating times, the intensity of the defect photoluminescence increases exponentially with an increase in the temperature with an activation energy of 0.85 eV, which is considerably higher than the activation energy (∼0.2 eV) determined from experiments on classical annealing. This and other experimental results on the temperature dependence of the intensity and kinetics of the defect photoluminescence have been explained in terms of the “hydrogen glass” model by thermally induced generation of intrinsic defects in amorphous silicon. The results of the calculations are in good agreement with the experimental data on the defect photoluminescence that reflects the formation and annihilation of defects for short heating times under optical excitation.     

Nickel-disilicide-assisted excimer laser crystallization of amorphous silicon

Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi多晶硅 受激准分子激光器结晶 结晶化 界面晶粒生长polycrystalline silicon, excimer laser crystallization,Ni-disilicide, Ni-metal-induced lateral crystallization, two-interface grain growthProject supported by the National High Technology Development Program of China (Grant No 2002AA303250) and by the National Natural Science Foundation of China (Grant No 60576056).9/7/2005 12:00:00 AM3/6/2006 12:00:00 AMPolycrystalline silicon （poly-Si） thin film has been prepared by means of nickel-disilicide （NiSi2） assisted excimer laser crystallization （ELC）. The process to prepare a sample includes two steps. One step consists of the formation of NiSi2 precipitates by heat-treating the dehydrogenated amorphous silicon （a-Si） coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy （SEM）, another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization （Ni-MILC） model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi2 precipitates and a-Si. The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi2 precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILC without migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved.     

Annealing and amorphous silicon passivation of porous silicon with blue light emission

The photoluminescence (PL) of the annealed and amorphous silicon passivated porous silicon with blue emission has been investigated. The N-type and P-type porous silicon fabricated by electrochemical etching was annealed in the temperature range of 700-900 °C, and was coated with amorphous silicon formed in a plasma-enhanced chemical vapor deposition (PECVD) process. After annealing, the variation of PL intensity of N-type porous silicon was different from that of P-type porous silicon, depending on their structure. It was also found that during annealing at 900 °C, the coated amorphous silicon crystallized into polycrystalline silicon, which passivated the irradiative centers on the surface of porous silicon so as to increase the intensity of the blue emission.     

Role of amorphous silicon domains of Er^3＋ emission in the Er—doped hydrogenated amorphous silicon suboxide film

An investigation on the correlation between amorphous Si (a-Si) domains and Er^{3+} emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H) film is presented. On one hand, a-Si domains provide sufficient carriers for Er^{3+} carrier-mediated excitation which has been proved to be the highest excitation path for Er^{3+} ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiO_x) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er^{3+} ions. This study provides a better understanding of the role of a-Si domains on Er^{3+} emission in a-Si:O:H films.     

The fabrication of nickel silicide ohmic contacts to n-type 6H-silicon carbide

This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi硅化镍;欧姆触点;n型碳化硅;制造;能带;带隙Project supported by the National Basic Research Program of China (Grant No~2002CB311904), the National Defense Basic Research Program of China (Grant No~51327010101) and the National Natural Science Foundation of China (Grant No~60376001).2006-09-192006-10-30This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi2/SiC structure axe formed on N-wells created by N^＋ ion implantation into Si-faced p-type 6H-SiC epilayer respectively. NiSi and NiSi2 films are prepared by annealing the Ni and Si films separately deposited. A two-step annealing technology is performed for decreasing of oxidation problems occurred during high temperature processes. The specific contact resistance Pc of NiSi contact to n-type 6H-SiC as low as 1.78× 10^-6Ωcm^2 is achieved after a two-step annealing at 350 ℃for 20 min and 950℃ for 3 min in N2. And 3.84×10-6Ωcm^2 for NiSi2 contact is achieved. The result for sheet resistance Rsh of the N＋ implanted layers is about 1210Ω/□. X-ray diffraction analysis shows the formation of nickel silicide phases at the metal/n-SiC interface after thermal annealing. The surfaces of the nickel silicide after thermal annealing are analysed by scanning electron microscope.     

Microstructural changes in amorphous Si/crystalline Al thin bilayer films upon annealing

Microstructural changes occurring in a sputter deposited Si (150 nm, amorphous)/Al (50 nm, crystalline); {111} fibre textured bilayer, upon annealing at 523 K for 60 min in a vacuum of 2.0×10^-4 Pa, were analyzed employing X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, atomic force microscopy and focused-ion beam imaging. After the annealing the Al and Si sublayers had largely exchanged their locations in the bilayer; i.e. the Si layer was adjacent to the substrate after annealing. Simultaneously, the amorphous Si layer had crystallized into an aggregate of {111} oriented nanocrystals, with a crystallite size of about 15 nm. The Al layer, now adjacent to the surface, had formed a uniformly net-shaped layer in association with an increase of the surface roughness. Upon this rearrangement, the already initially present Al {111} fibre texture had become stronger, the Al crystallites had grown laterally and the macrostress in the Al layer had relaxed. An extensive analysis of thermodynamic driving forces for the transformation indicated that the largest gain in energy upon transformation is due to the crystallization of the amorphous Si. The only identifiable driving force for the layer exchange appears to be the release of elastic energy upon the rearrangement of the Si and Al phases in the layer. PACS 61.43.D; 61.72.C; 62.40; 65.70; 68.55.J; 68.60.BThis revised version was published online in September 2004. Due to technical problems the PDF of the previous version was incomplete.     

高温高压下掺硼宝石级金刚石单晶生长特性的研究

本文在5.1—5.6 GPa,1230—1600℃的压力、温度条件下,以FeNiMnCo作为触媒,进行单质硼添加宝石级金刚石单晶的生长研究.借助于有限元法,对触媒内的温度场进行模拟.研究得到了FeNiMnCo-C-B体系下,金刚石单晶生长的P-T相图.该体系下合成金刚石单晶的最低压力、温度条件分别为5.1 GPa,1230℃左右.研究发现,在单晶同一{111}扇区内部,硼元素呈内多外少的分布规律.有限元模拟结果给出,该分布规律是由在晶体生长过程中,{111}扇区的增长速度逐渐减小所致.{111}晶向的晶体生长实验结果表明,硼元素优先从{111}次扇区进入晶体.研究发现,这是该扇区增长速度相对较快,硼元素扩散逃离可用时间短导致的.另外,同磨料级掺硼金刚石单晶生长相比,对于温度梯度法生长掺硼宝石级金刚石单晶,由于晶体的增厚速度较慢,即使硼添加量相对较高,也可以实现表面无凹坑缺陷的优质金刚石单晶的生长.     

Preferred orientations in nano-gold/silica/silicon interfaces

Gold in contact with silicon substrates Si(1 0 0), Si(1 1 1), and SiO₂ is studied by thermal evaporation and annealing in N₂ using the modified sphere-plate technique. The final orientation distribution of crystalline Au films grown on Si substrate systems that incorporate a native amorphous oxide layer of silica and Au on amorphous silica (SiO₂ glass) substrates is influenced by preferred orientations and twinning. Experimental evidence suggests that the orientation of Au{1 1 1} close packed planes (multiply twinned) was found to be of low-energy as the annealing temperature was increased to 530 °C and 920 °C. Additional orientations were observed for Au{1 0 0} on Si(1 0 0) substrates and Au{1 0 0}, {1 1 0}, and {3 1 1} on SiO₂ substrates. After annealing at 920 °C the size distribution of the gold particles was determined to be within the range of 20-800 nm while the morphology of gold surface appears spherical to faceted in character. These results show similarities to recent findings for smaller nano-size 1D particles, islands and thin Au films on silicon annealed over lower temperature ranges.     

Annealing embrittlement of Fe78Si9B13 (METGLAS-2605S2)

The ductile to brittle transition that occurs in amorphous Fe₇₈Si₉B₁₃ (METGLAS-2605S2) has been investigated using mechanical measurements over the temperature range 250–370 °C. The fracture toughness values, K _Ic , have been determined for a range of annealing times (5–30 min) and cooling rates of 15–45 °C/min. A pronounced ductile to brittle transition is observed around 310(10) °C although no obvious structural changes are evident as indicated by x-ray diffraction. Comparison of transmission and back-scattered conversion electron ⁵⁷Fe Mössbauer spectra for the bulk as-received ribbon in the ductile state ( $K_{Ic}=52~{\rm MPa} \cdot \sqrt{m}$ ) and the ribbon annealed to the brittle state ( $K_{Ic}\sim10~{\rm MPa} \cdot \sqrt{m}$ ) indicates magnetic texture effects in both the bulk and on the surface of these amorphous ribbons, related to the magnetostriction resulting from the quenched-in stress during the ribbon production process, and the ensuing stress-relief upon annealing.