Field emission measured from nanostructured germanium and silicon thin films

We have prepared nanostructured thin films of germanium and silicon. The films were grown by an ion beam sputtering technique followed by a rapid annealing step using an electron beam annealer. The annealing temperature is a comparatively low 500 °C, resulting in well defined nano-islands on the film surface. Electron field emission has been measured from the surfaces under high vacuum. The threshold electric field value for significant current flow was measured as 2.5 V μm⁻¹ for a silicon thin film which is comparable to other silicon technologies. A value of 0.5 V μm⁻¹ for a germanium thin film represents an order of magnitude improvement for related germanium nanostructured systems.     

Photoluminescence studies from silicon nanocrystals embedded in spin on glass thin films

Photoluminescence (PL) from silicon nanocrystals (Si-nc) prepared from pulverised porous silicon and embedded in undoped (SOG) or phosphorus-doped spin-on-glass (SOD) solutions was studied. Effects of rapid thermal annealing on the PL was also investigated. A strong room temperature PL signal was observed at 710 nm due to the recombination of electron-hole pairs in Si-nc and the PL maximum shifts to the blue region as the phosphorus concentration in the spin on glass increases. However, the rapid thermal annealing process (30 s, 900°C) quenches the PL response. These results suggest that for Si-nc/SOG (SOD) the surface termination is efficient but high phosphorus doping of Si-nc is detrimental to the PL.     

Laser crystallization for large-area electronics

Laser crystallization is reviewed for the purpose of fabrication of polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for formation of crystalline films with a low thermal budget. Reduction of electrically active defects located at grain boundaries is essential for improving electrical properties of poly-Si films and achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent developments in laser crystallization methods with pulsed and continuous-wave lasers are also reviewed. Control of heat flow results in crystalline grain growth in the lateral direction, which is important for fabrication of large crystalline grains. We also report an annealing method using a high-power infrared semiconductor laser. High-power lasers will be attractive for rapid formation of crystalline films over a large area and activation of silicon with impurity atoms.     

Effect of rapid thermal annealing on the properties of thin dielectric films of gadolinium, titanium, and erbium oxides on the silicon carbide surface

The effect of rapid thermal annealing on the properties of Ti, Ga, and Er oxide films on silicon carbide are studied by the methods of atomic force microscopy, monochromatic ellipsometry, optical absorption, and photoluminescence. The atomic composition of these films is analyzed as a function of the annealing time. The phase composition of the Ti, Ga, and Er oxide films on silicon carbide is shown to depend on the annealing time.     

Growth kinetics and polysilicon formation by aluminium-induced crystallization on glass-ceramic substrates

In this work, we present extended structural properties of poly-Si thin films fabricated by aluminium-induced crystallization (AIC) of amorphous silicon (a-Si) on high-temperature glass-ceramic substrates. The silicon nucleation kinetics on glass-ceramic substrates was investigated by optical microscopy. The crystalline quality of the films was studied by micro-Raman spectroscopy as a function of exchange annealing conditions. By means of electron backscattering diffraction (EBSD), we have analyzed the effect of thermal annealing on silicon grain size and its distribution, intra- and inter-grains defects, and on the grains preferential crystallographic orientation. The optimal thermal annealing condition, allowing 100% crystallized polysilicon large grains with an average grain size of 26 μm and 〈100〉 oriented, acquired a thermal budget of 475°C and 8 h.     

Processing for optically active erbium in silicon by film co-deposition and ion-beam mixing

Techniques of film deposition by co-evaporation, ion-beam assisted mixing, oxygen ion implantation, and thermal annealing were been combined in a novel way to study processing of erbium-in-silicon thin-film materials for optoelectronics applications. Structures with erbium concentrations above atomic solubility in silicon and below that of silicide compounds were prepared by vacuum co-evaporation from two elemental sources to deposit 200-270 nm films on crystalline silicon substrates. Ar⁺ ions were implanted at 300 keV. Oxygen was incorporated by O⁺-ion implantation at 130 keV. Samples were annealed at 600 °C in vacuum. Concentration profiles of the constituent elements were obtained by Rutherford backscattering spectrometry. Results show that diffusion induced by ion-beam mixing and activated by thermal annealing depends on the deposited Si-Er profile and reaction with implanted oxygen. Room temperature photoluminescence spectra show Er³⁺ transitions in a 1480-1550 nm band and integrated intensities that increase with the oxygen-to-erbium ratio.     

Modification of silicon waveguide structures using ion implantation induced defects

The structure of re-crystallized silicon films is investigated using transmission electron microscopy, spectroscopic ellipsometry and positron annihilation spectroscopy. Samples were prepared via amorphization of the silicon overlayer of silicon-on-insulator substrates, and subsequent thermal annealing. For an annealing temperature of 650 °C we show that the silicon film has a poly-crystalline structure. Its refractive index measured at 1550 nm is comparable to that of crystalline silicon following re-crystallization at 750 °C. Positron measurements indicate a high concentration of open-volume point defects in the re-crystallized films. We discuss the potential importance of these structures with regard to defect engineering for silicon photonic devices.     

Quantum states in fabricating poly-Si films

The quantum states are presented in these processions of fabricating poly-Si films. Amorphous silicon films prepared by PECVD has been crystallized by conventional furnace annealing (FA) and rapid thermal annealing (RTA), respectively. It is found that the thin films grain size present quantum states with the increasing of the gas flow ratios of SiH₄, H₂ mixture, substrate temperatures, frequency power, annealing temperature and time.     

c-axis-textured LiNbO3 thin films on Si (111) substrates

We have successfully prepared highly c-axis-textured LiNbO₃ films on hydrogen-terminated Si (111) substrate using sol-gel spin-coating and rapid thermal annealing. These highly c-axis-textured films were obtained with a preheating at 300 °C for 15 min followed by a rapid thermal annealing at 500–700 °C for 120 s. The c-axis orientation of the LiNbO₃ film is due to a weak effect caused by the 3-fold symmetry match between the film and the Si (111) substrate. The c-axis orientation of LiNbO₃ films is very useful in integrated optics devices and metal–ferroelectric–semiconductor nonvolatile memory applications. Received: 15 September / Accepted: 4 December / Published online: 3 April 2001     

Characterization of the crystallization behaviors in the PbTiO3 thin films on Si substrates by an infrared spectroscopy technique

PbTiO₃ thin films on silicon substrates derived from a modified sol–gel technique are characterized by IR reflectance spectroscopy for the first time. Seven infrared (IR) reflectance peaks modes have been observed in the crystallized perovskite PbTiO₃ thin films and are assigned to the corresponding phonon modes. Comparisons between the IR reflectance spectra of PbTiO₃ thin films obtained by different annealing processes, i.e., rapid thermal annealing (RTA) and conventional thermal annealing (CTA), have also been carried out. It is observed that the frequencies of most peaks in the RTA-derived PbTiO₃ films are lower than that in the CTA-derived films.     

High-conductive nanocrystalline silicon with phosphorous and boron doping

Intrinsic, P- and B-doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The microstructures, optical and electronic properties have been evaluated for the undoped and doped nanocrystalline films. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron and phosphorous in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the activation of dopant by annealing increased the room temperature dark conductivity from 3.4 × 10⁻⁴ S cm⁻¹ to 5.3 S cm⁻¹ for the P-doped films and from 1.28 × 10⁻³ S cm⁻¹ to 130 S cm⁻¹ for the B-doped films. Meanwhile, the corresponding value of conductivity activation energies was decreased from 0.29 eV to 0.03 eV for the P-doped films and from 0.3 eV to 5.6 × 10⁻⁵ eV for the B-doped films, which indicated the doped nc-Si films with high conductivity can be achieved with the present approach.     

Effect of different annealing methods on ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3-0.05PbTiO3 thin films

0.95Pb(Sc_0.5Ta_0.5)O₃-0.05PbTiO₃ thin films were prepared on LaNiO₃/SiO₂/Si substrate by radio frequency magnetron sputtering, and the films were annealed subsequently with repeated many times by two approaches: normal one-step rapid thermal annealing and innovative two-steps rapid thermal annealing. X-ray diffraction demonstrates that all the films were preferred (1 0 0) oriented and an appropriate repeat of annealing process can enhance perovskite phase of the films. Scanning electron microscopy suggests that the films treated by two-steps rapid thermal annealing show crack-free, uniform size grains and dense microstructure. Measurement of remnant polarization and leakage current dependence of electric field confirms that the films treated by two-steps rapid thermal annealing exhibit better ferroelectric properties than the films treated by one-steps rapid thermal annealing. The results reveal that microstructure plays an important role in enhanced ferroelectric properties of the 0.95Pb(Sc_0.5Ta_0.5)O₃-0.05PbTiO₃ thin films.     

磁控共溅射低温制备多晶硅薄膜及其特性研究

多晶硅在光电子器件领域具有较为重要的用途。利用磁控溅射镀膜系统,通过共溅射技术在玻璃衬底上制备了非晶硅铝(α-Si/Al)复合膜,将Al原子团包覆在α-Si基质中,膜中的Al含量可通过Al和Si的溅射功率比来调节。复合膜于N₂气氛中进行350 ℃,10 min快速退火处理,制备出了多晶硅薄膜。利用X射线衍射仪、拉曼光谱仪和紫外-可见光-近红外分光光度计对多晶硅薄膜的性能进行表征,研究了Al含量对多晶硅薄膜性能的影响。结果表明：共溅射法制备的α-Si/Al复合膜在低温光热退火下晶化为晶粒分布均匀的多晶硅薄膜;随着膜中Al含量逐渐增加,多晶硅薄膜的晶化率、晶粒尺寸逐渐增加,带隙则逐渐降低;Al/Si溅射功率比为0.1时可获得纳米晶硅薄膜,Al/Si溅射功率比为0.3时得到晶化率较高的多晶硅薄膜,通过Al含量的调节可实现多晶硅薄膜的晶化率、晶粒尺寸及带隙的可控。     

Rapid thermal annealing of ITO films

Tin-doped indium oxide (ITO) films with 200 nm thickness were deposited on glass substrates by DC magnetron sputtering at room temperature. And they were annealed by rapid thermal annealing (RTA) method in vacuum ambient at different temperature for 60 s. The effect of annealing temperature on the structural, electrical and optical properties of ITO films was investigated. As the RTA temperature increases, the resistivity of ITO films decreases dramatically, and the transmittance in the visible region increases obviously. The ITO film annealed at 600 °C by RTA in vacuum shows a resistivity of 1.6 × 10⁻⁴ Ω cm and a transmittance of 92%.     

Microstructure and magnetic properties of FePt:Ag nanocomposite films on SiO2/Si(1 0 0)

FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO₂/Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 °C.     

Low temperature N2-based passivation technique for porous silicon thin films

A technique is presented for the passivation of porous silicon (PS) thin films via nitrogen based annealing at the lowest temperature ever reported. Annealing freshly anodized PS thin films at temperatures as low as 520  ^°C under N₂ flow in a rapid thermal annealer produces films that show no change in refractive index when exposed to ambient conditions over 60 days. These films also exhibited chemical resistance by surviving a brief dip in both concentrated KOH and buffered HF. Unlike most other PS surface passivation methods, this technique causes negligible reduction in refractive index of the annealed PS thin films. Passivation only occurs when dangling bonds and mono-hydrides populate the PS surface, providing a path for thermal interactions with the N₂ gas.     

Correlation between optical properties and Si nanocrystal formation of Si-rich Si oxide films prepared by plasma-enhanced chemical vapor deposition

We have investigated the phase separation and silicon nanocrystal (Si NC) formation in correlation with the optical properties of Si suboxide (SiO_x, 0 < x < 2) films by thermal annealing in high vacuum. The SiO_x films were deposited by plasma-enhanced chemical vapor deposition at different nitrous oxide/silane (N₂O/SiH₄) flow ratios. The as-deposited films show increased Si concentration with decreasing N₂O/SiH₄ flow ratio, while the deposition rate and surface roughness have strong correlations with the flow ratio in the N₂O/SiH₄ reaction. After thermal annealing at temperatures above 1000 °C, Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy manifest the progressive phase separation and continuous growth of crystalline-Si (c-Si) NCs in the SiO_x films with increasing annealing temperature. We observe a transition from multiple-peak to single peak of the strong red-range photoluminescence (PL) with increasing Si concentration and annealing temperature. The appearance of the single peak in the PL is closely related to the c-Si NC formation. The PL also redshifts from ∼1.9 to 1.4 eV with increasing Si concentration and annealing temperature (i.e., increasing NC size). The good agreements of the PL evolution with NC formation and the PL peak energy with NC size distribution support the quantum confinement model.     

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (E_d) and the annealing temperature were varied from 123 to 242 mJ/cm² and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d ≥ 188 mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.     

Carrier transport of doped nanocrystalline Si formed by annealing of amorphous Si films at various temperatures

Phosphorus- and boron-doped hydrogenated amorphous silicon thin films were prepared by the plasma-enhanced chemical vapor deposition method. As-deposited samples were thermally annealed at various temperatures to get nanocrystalline Si with sizes around 10 nm. X-ray photoelectron spectroscopy measurements demonstrated the presence of boron and phosphorus in the doped films. It is found that the nanocrystallization occurs at around 600 °C for the B-doped films, while it is around 700-800 °C for the P-doped samples. For the P-doped samples, the dark conductivity decreases at first and then increases with the annealing temperature. While for the B-doped samples, the dark conductivity monotonously increases with increasing annealing temperature. As a result, the carrier transport properties of both P- and B-doped nanocrystalline Si films are dominated by the gradual activation of dopants in the films. The conductivity reaches 22.4 and 193 S cm⁻¹ for P- and B-doped sample after 1000 °C annealing.     

Effect of thermal annealing on the formation of silicon nanoclusters in SiOX films grown by PLD

Silicon nanoclusters formation in pulsed laser deposited (PLD) silicon suboxide (SiO_X) films by thermal annealing is reported. The SiO_X films are prepared by ablation of silicon target at different oxygen partial pressures. The different deposition conditions are employed to study the effect of oxygen concentration on the size of the nanoclusters. Post deposition thermal annealing of the films leads to the phase separation in silicon suboxide films. Fourier transform infrared spectroscopy, micro-Raman spectroscopy and UV-vis absorption spectroscopy studies were carried out to characterize the formation of silicon nanoclusters in SiO_X films.