BF2 ion implantation in silicon through surface oxides,behaviour of the fluorine with rapid thermal annealing

BF₂ ion implantation through surface oxides has been investigated to form shallow p⁺/n junctions. BF₂ ion implantation was performed at 25 keV at a dose of 5.4 × 10¹⁴cm⁻² through surface oxides of different thicknesses into crystalline silicon. Rapid thermal annealing (1000°C/10 s) was used for dopant activation and radiation damage removal. Secondary ion mass spectroscopy (SIMS) was used to obtain the boron and fluorine distribution profiles. p⁺/n junctions as shallow as 0.12 μm were formed with reasonable sheet resistance. The study shows that, as expected, dopant loss in the surface oxide during ion implantation results in higher values of sheet resistance. Out-diffusion of fluorine during RTA resulted in a fluorine loss of 50 to 65% from the silicon. Also, fluorine was found to segregate at the oxide/silicon interface.     

High-resolution electron microscopy of Zn- and Bi-related superlattices in ion implanted (1 0 0) Si

Nanosized precipitation in high-dose Zn⁺- and Bi⁺-implanted Si is investigated by high-resolution transmission electron microscopy of cross-sectional specimens. In spite of the different diffusivities of Zn and Bi in Si, their low solubility results in the precipitation of nanosized metallic inclusions revealed as superlattices composed of the host Si matrix and the implanted species.     

Microstructure of (100) silicon wafer implanted by 1 MeV Ru+ ions

A p-type device grade silicon wafer was implanted by 1 MeV Ru⁺ ions to a dose of 5.67 × 10¹⁶ cm^–2. The microstructures of the as-implanted and annealed samples were studied mainly by analytical transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that the implantation resulted in a well-defined surface layer of about 910 nm in thickness. The layer was composed of ultra-fine Ru₂Si₃ crystallites in an amorphous matrix. After annealing, the inner part of the layer recovered completely to single crystal Si with nano-scaled Ru₂Si₃ embedded in it. A 660 nm thick polycrystalline region consisting of Si and Ru₂Si₃ grains was formed at the surface.     

激光能量对碲镉汞注入样品退火效果的影响

利用脉冲ＹＡＧ激光器对砷注入长波碲镉汞样品进行激光退火、分析不同能量密度的激光光束退火所引起的样品表面电学性质的变化。实验表明,激光能量密度越大,激光退火的效果越明显。我们认为要达到理想退火效果,样品表面一薄层需处迂近熔化状态,以得到晶格结构的重新组织。     

Influence of pressure annealing on electrical properties of Mn implanted silicon

The effect of annealing at 610-720 K under enhanced hydrostatic pressure (HP) on electrical properties of manganese implanted Czochralski grown silicon (CzSi:Mn) and floating zone grown silicon (FzSi:Mn) (doses up to 1×10¹⁶ cm⁻¹, E=160 keV) was investigated by electrical C-V, I-V and admittance measurements. Mn⁺ implantation produces both donor-like and acceptor-like implantation-induced defects. The stress-induced decrease in the hole concentration was detected in CzSi implanted by Mn⁺ and annealed at temperatures 610-670 K. The effect of changing initial conductivity of CzSi:Mn samples of high concentration of interstitial oxygen, from p type to n type, due to thermal donors (TDs) generation has been observed. The electron concentration after type conversion depends on annealing conditions and Mn⁺ dose. The TDs generation has not been detected in FzSi:Mn samples containing lower oxygen concentration, however, the FzSi:Mn samples annealed at 720 K under 10⁵ Pa for 10 h indicate at the implanted side the increased carrier concentration due to the defects produced by Mn⁺ implantation. The heat treatment of FzSi:Mn under HP at 720 K for 10 h results in further increase of carrier concentration due to the defect generation.     

PAC investigations of radiation damage annealing in In implanted ZnO

The structural and electronic environment about implanted radioactive ¹¹¹In(→¹¹¹Cd) probe atoms as a function of annealing temperature in a single crystal of ZnO(0 0 0 1) has been monitored on an atomic scale using perturbed angular correlation technique, a nuclear hyperfine method. This technique is based upon the hyperfine interaction of the nuclear electric quadrupole moment or magnetic moment of the probes, respectively, with the electric field gradient or magnetic hyperfine field arising from the extra-nuclear electronic charges and spin distributions. The probe atoms ¹¹¹In were recoil-implanted at room temperature following heavy-ion nuclear reactions. The electric quadrupole interaction was measured at room temperature for as-implanted and annealed samples. The thermal annealing in ambient nitrogen up to 1000 °C showed a progressive reduction of disorder around the probe atom as evidenced via continual decrease in width of the distribution of quadrupole interaction frequencies. Present measurements suggested that annealing at 800 °C for 30 min in flowing nitrogen is enough to produce an optimum recovery of crystallinity. After annealing of radiation damage at 1000 °C we observed an axially symmetric electric field gradient which is characterized by the unique quadrupole interaction frequency of 30.6(3) MHz and a frequency distribution of width nearly zero. The observed electric field gradient was attributed to substitutional incorporation of probe atoms at cation-sites of ZnO. In contrast to annealing in ambient nitrogen at 1000 °C, air annealing of ¹¹¹In implanted ZnO samples revealed change in local stoichiometry about probe atoms which is attributed to the internal oxidation of the indium probes. The measured electric field gradient and asymmetry parameter at cation-sites of ZnO have been compared with theoretical calculations using a simple point charge model.     

Effect of high hydrostatic pressure during annealing on silicon implanted with oxygen

The effect of annealing of oxygen-implanted silicon (Si : O, oxygen doses 3.5×10¹⁷ cm^–2 and 6×10¹⁷ cm^–2; energy 140 keV and 170 keV) at high temperatures (HT, up to 1570 K) under enhanced hydrostatic pressure (HP, up to 1.2 GPa) for 5 h is investigated by means of structure-sensitive methods. It has been shown that the kind and concentration of defects created at HT–HP in Si : O and the homogeneity of the buried SiO₂ layer are markedly dependent on external stress applied at HT. Some differences between the formation processes of SiO₂ under normal conditions and at HP are discussed.     

Tilt-axis effect on oxidation behaviour and capacitance-voltage characteristics of (1 0 0) silicon

(1 0 0) Si and 4° off (1 0 0) Si were oxidized in dry oxygen, and the differences in thermal oxidation behaviour, oxidation-induced stacking faults and capacitance-voltage characteristics were investigated. The thickness of the oxide produced by oxidation of the silicon samples in dry oxygen in the temperature range 1000–1200°C was measured using an ellipsometer. The oxidation rates of the 4° off (1 0 0) Si were faster than those of the (1 0 0) Si but the differences between them decreased as the oxidation temperature increased. The size of the oxidation-induced stacking faults increased as the oxidation time and temperature increased from 1100 to 1200°C. The density of oxidation-induced stacking faults was lower for the 4° off (1 0 0) Si than for the (1 0 0) Si. Variations in the capacitance-voltage characteristics with the oxidation temperature showed that the flat band voltages were shifted positively. The fixed surface state charge density and the interface trapped charge density of the 4° off (1 0 0) Si were lower than those of the (1 0 0) Si. Si lattice strains induced by excess interstitial Si atoms were investigated through convergent beam electron diffraction. The lattice strain of the 4° off (1 0 0) Si was lower than that of the (1 0 0) Si and this showed that the 4° off (1 0 0) Si had a lower interstitial concentration. This revised version was published online in November 2006 with corrections to the Cover Date.     

Electronic properties of silicon nanocrystallites obtained by SiOx (x<2) annealing

Nanocrystal-based devices are possible candidates for future electronics. In this context, we have studied the electronic properties of Si nanocrystals (nc-Si) embedded in a SiO₂ matrix. This work is devoted to the characterization of nc-Si by means of morphological, optical and electrical techniques.SiO_x (x<2) layers are deposited by low-pressure chemical vapor deposition (LPCVD). Morphological measurements have shown that the as-deposited layers are homogeneous and that thermal annealing induces a precipitation of the excess silicon into nanocrystallites. Photoluminescence (PL) measurements show a large emission spectrum around 1.5 eV in agreement with the literature results for confined levels in 5-nm Si dots.Current–voltage (I–V) measurements recorded at different temperatures on metal-oxide-semiconductor (MOS) capacitors with nc-Si are analysed in terms of structural and electronic modifications induced by the annealing. The as-deposited SiO_x layers show a Poole–Frenkel conduction behavior. In annealed samples, it appears that the current follows a hopping transport mechanism. This is understood as a direct tunneling from dots to dots.Finally, it is shown that the annealed SiO_x is able to store carriers and is therefore a good candidate for non-volatile memory applications. Charging curves are presented and discussed with a model previously validated on MOS structures with silicon dots obtained by pure silane deposition.     

Two-dimensional modelling of diffusion of low-energy implanted arsenic in silicon at rapid thermal annealing

The two-dimensional model of arsenic diffusion in silicon at rapid thermal annealing is presented. A method of solving the nonlinear differential equations system is specified. Model calculations were performed for 15 keV As⁺ implanted in Si and annealed for 10 min at 950 °C. The results are in reasonable agreement with the experimental data, including the presence of local maximum of arsenic atoms near the surface.     

Effects of anisotropy and annealing on microhardness of In x Bi2−x Te3 (x=0·1 to 0·5) single crystals

The crystals of In _x Bi_2−x Te₃ (x=0·1 to 0·5) have been grown by zone-melting method. In order to study anisotropy exhibited by the (0001) plane of the crystals, the directional hardness was determined by producing indentations at various azimuthal orientations of the indentor with respect to the surface over a range 0–180°. The crystal was rotated about the indentor axis in steps of 15° while keeping applied load and loading time constant at 50 g and 20 sec, respectively. For annealing study, the sample was kept at a temperature of 375°C. It was observed that softening of crystal takes place and the hardness decreases to a considerable extent.     

Self-assembled germanium islands grown on (0 0 1) silicon substrates by low-pressure chemical vapor deposition

The time evolution of self-assembled Ge islands, during low-pressure chemical vapor deposition (LPCVD) of Ge on Si at 650 °C using high growth rates, has been investigated by atomic force microscopy, transmission electron microscopy, and Rutherford backscattering spectrometry. We have found three different island structures. The smallest islands are lens-shaped and characterized by a rather narrow size distribution, 4 nm high and 20 nm wide. Next to form are a distinct population of larger multifaceted dome-shaped islands, up to 25 nm high and 80–150 nm wide. Finally, the largest islands that form are square-based truncated pyramids with a very narrow size distribution, 50 nm high and 250 nm wide. The pyramidal islands normally seen in the intermediate size range (150 nm) are not observed. The small lens-shaped islands appear to be defect free, while some of the multifaceted islands as well as all the large truncated pyramids contain misfit dislocations. The existence of multifaceted islands, in the size range where pyramids have previously been reported and of truncated pyramids in the size range where multifaceted dome-shaped islands have previously been reported, is attributed to the high growth rate used. Furthermore, under the growth conditions used, the truncated-pyramid-shaped islands are characterized by a very narrow size distribution.     

退火工艺对WRe20热电偶丝材机械性能的影响

研究了退火工艺(退火方式,退火温度,速度,时间)对WRe20热电偶丝材机械性能的影响。发现在1 350℃,保温45min退火获得的0.4mm粗丝具有最佳的抗弯折性能;而0.104 mm细丝采用连续退火工艺,在1 100℃环境下以18 m/s的速度退火,其抗拉强度和延伸率最好,同时随退火温度的升高,丝材的抗拉强度下降而延伸率升高;对于退火条件相同而直径不同的丝材,其延伸率随丝径的减小而减小。研究结果表明合理的退火工艺,可以显著改善加工性能,利于丝材的进一步加工,提高成品率。     

Rutherford backscattering/channeling study of the implanted MeV Au+ in silicon

1.0 MeV Au⁺ ions were implanted into a Si single crystal and an amorphous silicon film at room temperature. For the case of the Si single crystal, ion implantation was performed at angles of 7, 45 and 60°, respectively. The amorphous silicon film was deposited on SiO₂ substrate with a thickness of ∼500 nm. The longitudinal and lateral distributions of implanted Au ions in silicon were measured by Rutherford backscattering spectrometry. The lateral spread was estimated from the tilt angle implantation. The results show that the experimental mean projected range is larger than the calculated value by ∼20%, and the experimental range straggling and lateral spread deviate significantly from the TRIM prediction. The damage in the Si single crystal induced by MeV Au⁺ under different fluences was studied by Rutherford backscattering/channeling. Also, the thermal behaviour of the implanted Au⁺ in silicon was investigated.     

Effects of morphologies of (Cd+Te) powders on the properties of sintered CdS/CdTe solar cells

Polycrystalline CdS/CdTe solar cells have been prepared by coating and sintering a CdS slurry and a (Cd+Te) slurry. CdS layers were first formed on borosilicate glass substrates at 600°C in nitrogen and then CdTe layers were formed on the sintered CdS layers at 625°C in nitrogen. The (Cd+Te) slurry contained (Cd+Te) powders mixed in a ball mill for 12–220 h instead of more expensive CdTe powders. The shape of cadmium particles changed from spherical to plate-like and the diameter of the plate-shaped particles became smaller as the ball-milling time increased. In addition, a compound CdTe started to form during a long milling time. The sintered CdTe layers were more compact as the diameter of plate-shaped cadmium particles decreased. However, cracks developed in the sintered CdTe layer when the diameter was small ( 2 m). The efficiency of sintered CdS/CdTe solar cells increased with decreasing particle diameter and then decreased with further decrease in particle diameter. The highest efficiency of 12.1% was achieved using a mixture of (Cd+Te) powders which had plate-shaped cadmium particles with a diameter of 5 m. The results suggest that high-efficiency sintered CdS/CdTe solar cells can be fabricated by using CdTe slurry from the mixture of (Cd+Te) powders with an inexpensive ball-milling process.     

Optical properties of ZnO nanowire arrays electrodeposited on n- and p-type Si(1 1 1): Effects of thermal annealing

Electrodeposition is a low temperature and low cost growth method of high quality nanostructured active materials for optoelectronic devices. We report the electrochemical preparation of ZnO nanorod/nanowire arrays on n-Si(1 1 1) and p-Si(1 1 1). The effects of thermal annealing and type of substrates on the optical properties of ZnO nanowires electroplated on silicon (1 1 1) substrate are reported. We fabricated ZnO nanowires/p-Si structure that exhibits a strong UV photoluminescence emission and a negligible visible emission. This UV photoluminescence emission proves to be strongly influenced by the thermal annealing at 150-800 °C. Photo-detectors have been fabricated based on the ZnO nanowires/p-Si heterojunction.     

The influence of channelling on radiation damage produced in silicon during ion bombardment

The ion bombardment of silicon results in the formation of an amorphous phase in the vicinity of the bombarded regions. This gives rise to a milky appearance which is easily distinguishable from an adjacent unbombarded region. An experiment is described which was specifically designed to study the influence of channelling of incident 80 keV Ne⁺ ions on the formation of this amorphous phase. It is found that channelling significantly reduces the rate at which this phase is produced, and in the particular case of the 110 axial channel this corresponds to a reduction in radiation damage by a factor of about 8. The results are compared with the current theories of channelling and are found to be in reasonable quantitative agreement.     

Molecular dynamics study of cluster impact on the (0 0 1) and (1 1 0) surfaces of fcc metals

Molecular dynamics simulations of the impact deposition of metal clusters on fcc metal surfaces are presented. Two-dimensional elongated islands are formed when the incident cluster travels parallel to the surface. For perpendicular incidence the results of the impact event are very sensitive to the relative cohesive properties of the cluster and substrate atoms.     

Growth of InAs quantum dots on focussed ion beam implanted GaAs(100)

The growth of self-assembled InAs quantum dots on implantation doped GaAs was studied. Be and Si ions were implanted in a combined ion implantation/molecular beam epitaxy process to generate p- and n-type GaAs, respectively. The quality of the InAs quantum dots was investigated by photoluminescence spectroscopy and scanning electron microscopy. By employing an in situ annealing step before re-growth it was possible to fabricate high quality InAs quantum dots on ion doped GaAs for Be doses up to 1.4×10¹⁴ cm⁻². The sheet resistance of the Be doped GaAs was as low as 1 kΩ at 300 K and 0.6 kΩ at 4.2 K, respectively. Only for rather low Si doses up to 5×10¹³ cm⁻² acceptable photoluminescence could be detected. The sheet resistance for these doses was 1 kΩ at 300 K and 1.7 kΩ at 4.2K.     

Effects of stress on the interfacial reactions of metal thin films on (0 0 1)Si

The influences of stress on the interfacial reactions of Ti and Ni metal thin films on (0 0 1)Si have been investigated. Compressive stress present in the silicon substrate was found to retard significantly the growth of Ti and Ni silicide thin films. On the other hand, the tensile stress present in the silicon substrate was found to enhance the formation of Ti and Ni silicides. For Ti and Ni on stressed (0 0 1)Si substrates after rapid thermal annealing, the thicknesses of TiSi₂ and NiSi films were found to decrease and increase with the compressive and tensile stress level, respectively. The results clearly indicated that the compressive stress hinders the interdiffusion of atoms through the metal/Si interface, so that the formation of metal silicide films was retarded. In contrast, tensile stress facilitates the interdiffusion of atoms. As a result, the growth of Ti and Ni silicide is promoted.