Epitaxial growth and optical characterization of compound semiconductor β-FeSi2 prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on FZ n-Si (1 1 1) substrates by pulsed laser deposition (PLD). The structural properties and crystallographic orientation of the films were investigated by X-ray diffraction (XRD) analysis. This indicates that β-FeSi₂/Si (2 0 2/2 2 0) and the single-crystalline β-FeSi₂ can be prepared using PLD. In photoluminescence (PL) measurements at 8 K detected by Ge detector, the PL spectra of the samples annealed at 900 °C for 1, 5, 8 and 20 h showed that the PL intensity of the A-band peak increased depending on annealing time in comparison with those of as-deposited samples. The intrinsic PL intensity of the A-band peak at 0.808 eV of the β-FeSi₂ from the 20-h-annealed sample was investigated for the first time by the PLD method detected by an InGaAs detector. This result has been confirmed by temperature dependence and excitation power density of the 20-h-annealed sample with the comparison of other defect-related band peaks of the sample. Cross-sectional scanning electron microscopy (SEM) observation was also performed and the thickness of the thin films was found to be at 75 nm for 20-h-annealed. The thermal diffusion for the epitaxial growth of β−FeSi₂/Si was observed when the compositional ratio of Fe to Si was around Fe:Si=1:2 for 20-h-annealed carried out by energy dispersive X-ray spectroscopy (EDX). We discussed high crystal quality of the epitaxial growth and optical characterization of β-FeSi₂ achieved after annealing at 900 °C for 20 h.     

Correlation between impurities in Fe-Si amorphous layers synthesized by Fe implantation and photoluminescence property of β-FeSi2 precipitates in Si

Completely amorphous Fe-Si layers are formed by Fe implantation into Si substrate at a dosage of 5×10¹⁵ cm⁻² using a metal vapor vacuum arc (MEVVA) ion source under 80 kV extraction voltage and cryogenic temperature. After thermal annealing, β-FeSi₂ precipitates are formed in Si matrix. The influence of impurities in these amorphous Fe-Si layers on the photoluminescence (PL) from β-FeSi₂ precipitates is investigated. PL is found to be significantly enhanced by optimizing the impurity concentration and annealing scheme. After 60 s of rapid thermal annealing (RTA) at 900 °C, β-FeSi₂ precipitates in medium boron-doped Si substrate give the strongest PL intensity without boron out-diffusion from them.     

Optical properties of single-phase β-FeSi2 films fabricated by electron beam evaporation

Single-phase semiconducting iron disilicide (β-FeSi₂) films on silicon substrate were fabricated by electron beam evaporation (EBE) technique. For preventing the oxidation of Fe film, silicon/iron/silicon sandwich structure films with different thickness of silicon and iron were deposited and then annealed at different temperatures. X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR) measurements were carried out to study the phase distribution and crystal quality of the films. Single-phase β-FeSi₂ with high crystal quality was achieved after annealing at 800 °C for 5 h. An apparent direct bandgap E_g of approximately 0.85-0.88 eV was observed in the β-FeSi₂ films. It is considered that the silicon/iron/silicon sandwich structure is suited for formation of single-phase β-FeSi₂ with high crystal quality.     

Growth of β-FeSi2 thin film on textured silicon substrate for solar cell application

(2 0 2)/(2 2 0)-oriented epitaxial β-FeSi₂ thin films were deposited on textured Si (1 0 0) substrate by magnetron sputtering. The influences of thickness and annealing temperature on the β-FeSi₂ crystallization were studied to find the optimal condition. The results of surface morphology and optical property measurements showed that the inverted pyramid array in the surface of β-FeSi₂ thin films could reduce the surface reflection of β-FeSi₂. In dark condition, the β-FeSi₂/textured-Si heterojunction showed diode property with rectifying ratio of 2.89 × 10⁵ and built-in potential of 0.58 V. These results indicated the potential application of textured Si substrate in β-FeSi₂ solar cells.     

Initial stages of iron silicide formation on the Si(1 0 0)2 × 1 surface

The initial stages of iron silicide growth on the Si(1 0 0)2 × 1 surface during solid-phase synthesis were investigated by photoelectron spectroscopy using synchrotron radiation. The experiments were made on iron films of 1-50 monolayer (ML) thickness in the temperature range from room temperature to 750 °С. Our results support the existence of three stages in the Fe deposition on Si(1 0 0) at room temperature, which include formation of the Fe-Si solid solution, Fe₃Si silicide and an iron film. The critical Fe dose necessary for the solid solution to be transformed to the silicide is found to be 5 ML. The solid-phase reaction was found to depend on the deposited metal dose. At 5 ML, the reaction begins at 60 °С, and the solid-phase synthesis leads to the formation of only metastable silicides (FeSi with the CsCl-type structure, γ-FeSi₂ and α-FeSi₂). A specific feature of this process is Si segregation on the silicide films. At a thickness of 15 ML and more, we observed only stable phases, namely, Fe₃Si, ε-FeSi and β-FeSi₂.     

Surface morphology and luminescence characterization of β-FeSi2 thin films prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on Si (1 1 1) substrates by pulsed laser deposition (PLD) with a sintering FeSi₂ target and an electrolytic Fe target. The thin films without micron-size droplets were prepared using the electrolytic Fe target; however, the surface without droplets was remarkably rougher using the Fe target than using the FeSi₂ target. After deposition at 600 °C and then annealing at 900 °C for 20 h, XRD indicated that the thin film prepared using the Fe target had a poly-axis-orientation, but that prepared using the FeSi₂ target had a one-axis-orientation. The PL spectra of the thin films prepared using the FeSi₂ and Fe targets at a growth temperature of 600 °C and subsequently annealed at 900 °C for 20 h had A-, B- and C-bands. Moreover, it was found that the main peak at 0.808 eV (A-band) in the PL spectrum of the thin films prepared using the FeSi₂ target was the intrinsic luminescence of β-FeSi₂ from the dependence of PL peak energy on temperature and excitation power density.     

Growth process of β-FeSi2 epitaxial film on Si(1 1 1) by molecular beam epitaxy

We have reported a one step growth of a high quality β-FeSi₂ epitaxial film on hydrogen terminated Si(1 1 1) by using molecular beam epitaxy (MBE) without template layer or post-growth annealing. In the present work, the growth process was studied by analyzing X-ray diffraction (XRD) spectra, reflective high energy electron diffraction (RHEED) and atomic force microscopy (AFM) observations on the samples grown with different growth times from 10 s to 1 h. A phase transformation from γ-FeSi₂ to β-FeSi₂ was confirmed existing in the crystal film growth, as well as the growth mode changing from three-dimensional (3D) to two-dimensional (2D) mode.     

Formation of ultrathin iron silicide layers on the single-crystal silicon surface

The solid-phase synthesis of iron silicides on the Si(100)2 × 1 surface with a 5-ML-thick iron film deposited at room temperature was studied by high-resolution photoelectron spectroscopy with the use of synchrotron radiation. Computer simulation of the measured Si 2p spectra revealed the formation of silicides in this system already under annealing at a temperature of 60°C. The process of formation consists in successive syntheses of three iron silicide phases, more specifically, monosilicide ε-FeSi, metastable disilicide γ-FeSi₂, and disilicide β-FeSi₂. The temperature ranges of existence of these phases were determined. Silicon was found to segregate on the γ-FeSi₂ surface.     

纳米β-FeSi2/a-Si多层膜室温光致发光分析

采用射频磁控溅射的方法,在Si（100）基片上制备了纳米β-FeSi₂/Si多层结构,利用X射线衍射、透射电子显微镜、光致发光光谱等表征技术,研究了β-FeSi₂/Si多层结构的结构、成分和光致发光特性.研究结果表明：利用磁控溅射法得到的Fe/Si多层膜,室温下能够检测到β-FeSi₂的1.53 μm处光致发光信号;未退火时多层膜是（非晶的FeSi₂+β-FeSi₂颗粒）/非晶Si结构,退火后则是 关键词： 2')" href="#">β-FeSi₂ 磁控溅射 XRD 光致发光光谱     

The effects of substrate temperature on the structure, morphology and photoluminescence properties of pulsed laser deposited SrAl2O4:Eu,Dy thin films

In this study, SrAl₂O₄:Eu²⁺,Dy³⁺ thin film phosphors were deposited on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique. The films were deposited at different substrate temperatures in the range of 40-700 °C. The structure, morphology and topography of the films were determined by using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) data was collected in air at room temperature using a 325 nm He-Cd laser as an excitation source. The PL spectra of all the films were characterized by green phosphorescent photoluminescence at ∼530 nm. This emission was attributed to 4f⁶5d¹→4f⁷ transition of Eu²⁺. The highest PL intensity was observed from the films deposited at a substrate temperature of 400 °C. The effects of varying substrate temperature on the PL intensity were discussed.     

Transmission electron microscopy studies of HfO2 thin films grown by chloride-based atomic layer deposition

Detailed transmission electron microscopy characterization of HfO₂ films deposited on Si(1 0 0) using atomic layer deposition has been carried out. The influence of deposition temperature has been investigated. At 226 °C, a predominantly quasi-amorphous film containing large grains of cubic HfO₂ (a₀ = 5.08 Å) was formed. Grain morphology enabled the nucleation sites to be determined. Hot stage microscopy showed that both the cubic phase and the quasi-amorphous phase were very resistant to thermal modification up to 500 °C. These observations suggest that nucleation sites for the growth of the crystalline cubic phase form at the growing surface of the film, rather homogeneously within the film. The films grown at higher temperatures (300-750 °C) are crystalline and monoclinic. The principal effects of deposition temperature were on: grain size, which coarsens at the highest temperature; roughness with increases at the higher temperatures due to the prismatic faceting, and texture, with texturing being strongest at intermediate temperatures. Detailed interfacial characterization shows that interfacial layers of SiO₂ form at low and high temperatures. However, at intermediate temperatures, interfaces devoid of SiO₂ were formed.     

Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

NbN_x films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 °C, on the preferred orientation, phase, and surface properties of NbN_x films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN_x films. For a substrate temperature up to 450 °C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650−850 °C, mix of cubic δ-NbN and hexagonal phases (β-Nb₂N + δ′-NbN) were formed. Films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperature above 850 °C. The c/a ratio of β-Nb₂N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN_x films increased as the temperature was raised from 450 to 850 °C.     

Fabrication, morphology, and photoluminescence properties of GaN nanowires and nanorods by ammoniating Ga2O3/V films on Si(1 1 1)

GaN nanowires and nanorods have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/V films at 900 °C in a quartz tube. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectrum were carried out to characterize the structure, morphology, and photoluminescence properties of GaN sample. The results show that the GaN nanowires and nanorods with pure hexagonal wurtzite structure have good emission properties. The growth direction of nanostructures is perpendicular to the fringes of (1 0 1) plane. The growth mechanism is also briefly discussed.     

Synthesis of molybdenum silicide by both ion implantation and ion beam assisted deposition

Two groups of Mo/Si films were deposited on surface of Si(1 0 0) crystal. The first group of the samples was prepared by both ion beam assisted deposition (IBAD) and metal vapor vacuum arc (MEVVA) ion implantation technologies under temperatures from 200 to 400 °C. The deposited species of IBAD were Mo and Si, and different sputtering Ar ion densities were selected. The mixed Mo/Si films were implanted by Mo ion with energy of 94 keV, and fluence of Mo ion was 5 × 10¹⁶ ions/cm². The second group of the samples was prepared only by IBAD under the same test temperature range. The Mo/Si samples were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), sheet resistance, nanohardness, and modulus of the Mo/Si films were also measured. For the Mo/Si films implanted with Mo ion, XRD results indicate that phase of the Mo/Si films prepared at 400 and 300 °C was pure MoSi₂. Sheet resistance of the Mo/Si films implanted with Mo ion was less than that of the Mo/Si films prepared without ion implantation. Nanohardness and modulus of the Mo/Si films were obviously affected by test parameters.     

Photoluminescence in amorphous (PbLa)TiO3 thin films deposited on different substrates

Pb_1−XLa_XTiO₃ thin films, (X=0.0; 13 and 0.27 mol%) were prepared by the polymeric precursor method. Thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1), Si (1 0 0) and glass substrates by spin coating, and annealed in the 200-300°C range in an O₂ atmosphere. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used for the microstructural characterization of the thin films. Photoluminescence (PL) at room temperature has been observed in thin films of (PbLa)TiO₃. The films deposited on Pt/Ti/SiO₂/Si substrates present PL intensity greater than those deposited on glass and silicon substrates. The intensity of PL in these thin films was found to be dependent on the thermal treatment and lanthanum molar concentration.     

Spectroscopic characterization of β-FeSi2 single crystals and homoepitaxial β-FeSi2 films by XPS and XAS

Chemical state analysis by a combination of X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) using synchrotron radiation is performed for β-FeSi₂ single crystals and homoepitaxial β-FeSi₂ films. The Si 2p XPS and Fe L-edge XAS spectra imply that the annealing at 1173 K to remove native oxide layers on the crystal induces the formation of FeSi in the surface. The formation of FeSi is also confirmed by Si K-edge XAS analysis. For the homoepitaxial β-FeSi₂ films grown on the crystals, the Si K-edge XAS spectra indicate that structurally homogeneous β-FeSi₂ films can be grown on the β-FeSi₂ single crystals when the substrate temperatures of 973 and 1073 K are applied for molecular beam epitaxy (MBE). Consequently, it is indicated that the combination of XPS and XAS using synchrotron radiation is a useful tool to clarify chemical states of β-FeSi₂ single crystals and homoepitaxial β-FeSi₂ films, which is important to reveal optimized growth conditions of homoepitaxial films.     

Role of growth temperature and oxygen partial pressure on the structural and electrical properties of pulsed laser deposited La1−xSrxnO3−δ thin films

The paper presents the fabrication and characterization of La_0.65Sr_0.35MnO_3−δ (LSMO) polycrystalline thin films deposited directly on Si (1 0 0) substrates using pulsed laser deposition technique. Various deposition parameters like substrate temperature and oxygen partial pressure have been varied systematically to obtain stoichiometric, crack-free films with smooth surface morphology having nearly monodisperse grain size distribution. The substrate temperature variation from 600 to 800 °C had profound effects on the microstructure and topography of the deposited film, with optimum result being obtained at 700 °C. The variation of partial pressure of oxygen controls the deposition kinetics as well as the stoichiometry of the film in terms of oxygen vacancy, which influences the magnetic and electrical transport properties of the manganate films. The microstructure and crystallinity of the deposited films have been studied using X-ray diffraction, scanning electron microscopy and atomic force microscopy. A correlation between the oxygen stoichiometry and micro-structural and transport properties of the deposited films has been obtained.     

Influence of deposition temperature on the structural and morphological properties of Be3N2 thin films grown by reactive laser ablation

Be₃N₂ thin films have been grown on Si(1 1 1) substrates using the pulsed laser deposition method at different substrate temperatures: room temperature (RT), 200 °C, 400 °C, 600 °C and 700 °C. Additionally, two samples were deposited at RT and were annealed after deposition in situ at 600 °C and 700 °C. In order to obtain the stoichiometry of the samples, they have been characterized in situ by X-ray photoelectron (XPS) and reflection electron energy loss spectroscopy (REELS). The influence of the substrate temperature on the morphological and structural properties of the films was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The results show that all prepared films presented the Be₃N₂ stoichiometry. Formation of whiskers with diameters of 100-200 nm appears at the surface of the films prepared with a substrate temperature of 600 °C or 700 °C. However, the samples grown at RT and annealed at 600 °C or 700 °C do not show whiskers on the surface. The average root mean square (RMS) roughness and the average grain size of the samples grown with respect the substrate temperature is presented. The films grown with a substrate temperature between the room temperature to 400 °C, and the sample annealed in situ at 600 °C were amorphous; while the αBe₃N₂ phase was presented on the samples with a substrate temperature of 600 °C, 700 °C and that deposited with the substrate at RT and annealed in situ at 700 °C.     

Effect of the laser fluence on the surface characterization of β-FeSi2 films prepared by pulsed laser deposition

Single-phase β-FeSi₂ films on silicon (1 0 0) were fabricated by pulse laser deposition. The structure and crystal quality of the samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The field scanning electron microscopy showed that the film thickness increases with the increasing of the laser fluence. Moreover, atomic force microscopy observations revealed the changes of surface properties with different laser fluence. Based upon all experimental results, it is found that 7 J/cm² is the most favorable for the formation of β-FeSi₂ thin films.     

Effects of buffer layer annealing temperature on the structural and optical properties of hydrothermal grown ZnO

ZnO was deposited on bare Si(1 0 0), as-deposited, and annealed ZnO/Si(1 0 0) substrates by hydrothermal synthesis. The effects of a ZnO buffer layer and its thermal annealing on the properties of the ZnO deposited by hydrothermal synthesis were studied. The grain size and root mean square (RMS) roughness values of the ZnO buffer layer increased after thermal annealing of the buffer layer. The effect of buffer layer annealing temperature on the structural and optical properties was investigated by photoluminescence, X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Hydrothermal grown ZnO deposited on ZnO/Si(1 0 0) annealed at 750 °C with the concentration of 0.3 M exhibits the best structural and optical properties.