An EPR study of defects induced in 6H-SiC by ion implantation

Crystalline (0001) plane wafers of n-type 6H-SiC have been implanted at room temperature with 200 keV Ge⁺ ions in the dose range 10¹² to 10¹⁵ cm⁻². Electron paramagnetic resonance (EPR) measurements have been made on these samples both before and after annealing them at temperatures in the range room temperature to 1500°C. The as-implanted samples have a single isotropic and asymmetric line EPR spectrum whose width, ΔB_pp, increases with ion dose before falling when a buried continuous amorphous layer is produced. This increase is interpreted in terms of the change in the relative intensity of a line with g = 2.0028 ± 0.0002, ΔB_pp = 0.4 mT associated primarily with carbon dangling bonds in a-SiC and a line with g in the range 2.0033 to 2.0039 of uncertain origin. The variation with anneal temperature of the populations of these defects is reported.     

Study of light-induced annealing effects in a-Si:H thin films

Light-induced metastability was examined in hydrogenated amorphous silicon thin films using a 500 W xenon lamp and a 10 mW HeCd laser. Positron beam annihilation spectroscopy (PAS) and fourier transform infrared spectroscopy (FTIR) were examined to investigate the effects of light on the structural properties of the films. The experimental results exhibited significant decrease in the S-parameter of the PAS, indicating marked reduction in the defect density of the films. The FTIR spectroscopy showed significant reduction in the transmission coefficient of IR radiation at frequencies corresponding to Si–H and Si–H₃ phonon modes, indicating that the observed annealing effects were due to light-induced formation of Si–H and Si–H₃ bonds. A second thermal annealing process conducted after the light exposure experiment resulted in a further substantial decrease in defect density for the sample exposed to HeCd laser. The experimental results are explained by a competing, light induced, dangling bond creation/annealing process, in which the incoming photons caused the annealing of dangling bonds, particularly those at around the voids. However, in the bulk region, the photons caused both the breaking of weak Si–Si bonds as well as the annealing of dangling bonds.     

Identification of a Three-Site Defect in Semi-Insulating 4H-SiC

Using electron paramagnetic resonance (EPR), we observe a defect that increases significantly with annealing temperature. This spin S = 1 defect is characterized by g _x ≈ g _y ≈ g _z = 2.0056 and a fine structure splitting D ∼ 100 G whose principal axis lies in a plane perpendicular to the c-axis. Also resolved are several hyperfine interactions with the low abundance ²⁹Si and ¹³C neighboring nuclei. A careful analysis of the intensity of these hyperfine lines allows a precise determination of the identity and the quantity of interacting nuclei. This center is diamagnetic in the ground state but can be excited into a paramagnetic triplet state by sub-bandgap light. We identify this new defect as a three-site vacancy involving V _C-V _Si-V _C. The angular dependence of the ¹³C hyperfine interaction supports the proposed model. These may be the simplest of a family of more complex and extended defects that play a role in the semi-insulating (SI) character of SiC.     

Molecular dynamics study on splitting of hydrogen-implanted silicon in Smart-Cut® technology

Defect evolution in a single crystal silicon which is implanted with hydrogen atoms and then annealed is investigated in the present paper by means of molecular dynamics simulation. By introducing defect density based on statistical average, this work aims to quantitatively examine defect nucleation and growth at nanoscale during annealing in Smart-Cut~ technology. Research focus is put on the effects of the implantation energy, hydrogen implantation dose and annealing temperature on defect density in the statistical region. It is found that most defects nucleate and grow at the annealing stage, and that defect density increases with the increase of the annealing temperature and the decrease of the hydrogen implantation dose. In addition, the enhancement and the impediment effects of stress field on defect density in the annealing process are discussed.     

Effect of annealing in an atomic-hydrogen atmosphere on the properties of amorphous hydrated silicon films and the parameters of p-i-n structures based on them

The decrease in the density of dangling silicon-silicon bonds in a-Si:H films as a result of annealing in an atomic-hydrogen atmosphere is determined by their density in the initial (nonannealed) film. The change in the total hydrogen density in a-Si:H films, annealed in an atomic-hydrogen atmosphere, is determined by the type of silicon-hydrogen bonds and the impurity content: The hydrogen content can decrease to 1 at. % in the presence of monohydride bonds (2020 cm⁻¹) and no change is observed in the hydrogen content in the presence of oxygen (≲0.1 at. %). A decrease in the defect density as a result of annealing in an atomic-hydrogen atmosphere is observed for all films. The Staebler-Wronski effect — AM-1 irradiation for 10 h — is observed for all films irrespective of the total hydrogen density, the type of silicon-hydrogen bonds, and the presence of oxygen. Fiz. Tekh. Poluprovodn. 32, 620–626 (May 1998)     

Effect of copper and chlorine on the properties of SiO2 encapsulated polycrystalline CdSe films

The effects of different copper doping concentrations on the properties of SiO₂ encapsulated CdSe films have been investigated. Two methods were used to dope the films with copper: ion implantation and diffusion from a surface layer. The room temperature dark resistivity of films annealed in oxygen at 450°C was found to increase as the copper concentration was increased until a maximum resistivity of 10⁸ ohm cm occurred at a copper concentration of 10²⁰ atoms cm⁻³. The room temperature resistivity in the light was found to be independent of the copper concentration and whether the films were annealed in argon or oxygen. During annealing the grains grew from 0.03 μm to 0.3 μm and this growth was independent of the doping or the annealing ambient. The energy levels, carrier mobilities, and microstructure of the annealed films were dependent on the method of doping. The ion implanted films had an additional energy level at 0.33 eV and their mobility was a factor of 4 smaller than films doped by the surface diffusion method, whose mobilities were 20 to 35 cm²V⁻¹ s⁻¹. The addition of chlorine to copper doped films had no effect on either the resistivity or photosensitivity but slowed the response times of the photocurrent by a factor of 10. No energy levels were observed which could be associated with the copper nor was the copper found to affect the density of the observed intrinsic levels at 0.65 and 1.1 eV.     

Effect of si—h and n—h bonds on electrical properties of plasma deposited silicon nitride and oxynitride films

Strong correlations were observed between the improvement in the metal-insulator-semiconductor (MIS) (aluminum-nitride-semiconductor) electrical properties of plasma deposited silicon nitride and oxynitride films and their (Si—H/N—H) bonding ratios in the film bulk. Total hydrogen concentration and spin density of all deposited films decreased with post-deposition annealing. Films with more Si—H bonds and stable (Si—H/ N—H) ratios generally have lowerV _fb shift, less positive trap charge and higher breakdown dielectric strength. Silicon oxynitride films with refractive indices of 1.75-1.80, as-deposited and after annealing in forming gas (10% H₂ + 90% N₂) at various temperatures, were found to have stable (Si—H/N—H) bonding ratios, lower silicon dangling bond density, and better MIS electrical properties compared to other plasma deposited nitride and oxynitride films.     

Effect of hydrostatic pressure during the annealing of silicon-on-insulator films implanted with a high hydrogen-ion dose

The properties of silicon-on-insulator films implanted with high hydrogen-ion doses (～50 at %) and annealed under a pressure of 10.5 kbar are studied using the Raman scattering (RS) method. A high degree of optical-phonon localization is detected in the films under study, which is retained to an annealing temperature of ～1000°C and is explained by the formation of silicon nanocrystals. It is found that the activation energy of annealing of the structural relaxation of dangling bonds in films with a high hydrogen content is independent of the annealing pressure. The activation energy of growth of the crystalline phase, calculated from RS spectra is ～1.5 eV and is independent of pressure. The effect of hydrostatic pressure consists only in a decrease in the frequency factor limiting Si-Si bond relaxation during ordering.     

射频磁控溅射法沉积非晶InGaZnO薄膜及真空退火对其性能的影响

采用RF磁控溅射法在石英玻璃上制备了InGaZnO薄膜,并对薄膜进行了真空退火实验,探讨了沉积过程中氧气流量及真空退火温度对薄膜的光学性质和电学性质的影响及其机理。测试结果表明薄膜的光透过率随氧气流的增加而增大,且当氧气流大于1cm3/min时,薄膜呈现出不导电性,在通入的氧气流为0.5cm3/min时迁移率达11.9cm2/(V·s)。经过真空退火后,氧气流小于1.5cm3/min时薄膜载流子浓度随退火温度的变化而变化;氧气流大于1.5cm3/min时样品由半绝缘性转变为半导电性。生长样品和退火样品均为n型半导体。     

Effect of Annealing Ambient on the Electrical and Optical Properties of Aluminum-Doped ZnO Films Produced via a Sol–Gel Process

In this study, aluminum-doped ZnO (AZO) thin films were prepared by a sol–gel with spin coating process. The AZO films were annealed by a two-step process. The films were first annealed in air or nitrogen at 500°C for 3 h, followed by annealing in three types of ambient, i.e., vacuum (10^?3 Torr or 10^?6 Torr) or forming gas (10% H₂/90% N₂), at 500°C for 4 h. The effect of the annealing ambient on the microstructure, electrical and optical properties of the AZO films was explored by x-ray diffraction, field-emission scanning electron microscopy, four-point probe sheet resistivity measurements, Hall voltage measurements, and ultraviolet–visible spectroscopy. The results showed that the size of AZO particulates in the films was determined mainly by the first annealing step. The films annealed in air in the first step were composed of larger AZO particulates than those annealed in nitrogen. The conductivities of the AZO films were significantly increased by the second annealing step. Second annealing in a high-vacuum system (10^?6 Torr) led to the highest AZO film conductivity among the three ambients. Regardless of the various annealing processes, the films remained transparent under visible light and exhibited a sharp absorption edge in the ultraviolet region. The highest conductivity, i.e., 168 S cm^?1, was obtained from films annealed first in air and then in vacuum of 10^?6 Torr.     

Low temperature processed hafnium oxide: Structural and electrical properties

In this work hafnium oxide (HfO₂) was deposited by r.f. magnetron sputtering at room temperature and then annealed at 200 °C in forming gas (N₂+H₂) and oxygen atmospheres, respectively for 2, 5 and 10 h. After 2 h annealing in forming gas an improvement in the interface properties occurs with the associated flat band voltage changing from −2.23 to −1.28 V. This means a reduction in the oxide charge density from 1.33×10¹² to 7.62×10¹¹ cm⁻². After 5 h annealing only the dielectric constant improves due to densification of the film. Finally, after 10 h annealing we notice a degradation of the electrical film's properties, with the flat band voltage and fixed charge density being −2.96 V and 1.64×10¹² cm⁻², respectively. Besides that, the leakage current also increases due to crystallization. On the other hand, by depositing the films at 200 °C or annealing it in an oxidizing atmosphere no improvements are observed when comparing these data to the ones obtained by annealing the films in forming gas. Here the flat band voltage is more negative and the hysteresis on the C–V plot is larger than the one recorded on films annealed in forming gas, meaning a degradation of the interfacial properties.     

Post-annealing effects on structural and magnetic properties of Mn–N codoped ZnO thin films

The sputtered ZnO:Mn thin films were implanted with nitrogen ions (N⁺) and subsequently annealed at different temperatures up to 800 °C in N₂ atmosphere. The structural and magnetic properties of the samples were systematically investigated. Both x-ray diffraction and Raman analyses reveal that all the films are of the wurtzite structure of ZnO with no distinct evidence of secondary phases. X-ray photoelectron spectroscopy studies indicate that both Mn²⁺ and N³⁻ ions were incorporated into ZnO lattice successfully. While the films without nitrogen ions show paramagnetic behavior, ferromagnetism with clear hysteresis at 300 K is observed in Mn–N codoped ZnO films. Most importantly, we also found that the magnetic behavior of the codoped ZnO is very sensitive to the annealing temperature due to its effect on the activation of nitrogen ions. The strongest ferromagnetism is obtained in the films with the highest amount of nitrogen ions acceptors. Our results support the predication that the ferromagnetic ZnO:Mn²⁺ should be more stable of a hole-rich environment by theory.     

High performance sol–gel spin-coated titanium dioxide dielectric based MOS structures

High-κ TiO₂ thin films have been fabricated using cost effective sol–gel and spin-coating technique on p-Si (100) wafer. Plasma activation process was used for better adhesion between TiO₂ films and Si. The influence of annealing temperature on the structure-electrical properties of titania films were investigated in detail. Both XRD and Raman studies indicate that the anatase phase crystallizes at 400 °C, retaining its structural integrity up to 1000 °C. The thickness of the deposited films did not vary significantly with the annealing temperature, although the refractive index and the RMS roughness enhanced considerably, accompanied by a decrease in porosity. For electrical measurements, the films were integrated in metal-oxide-semiconductor (MOS) structure. The electrical measurements evoke a temperature dependent dielectric constant with low leakage current density. The Capacitance–voltage (C–V) characteristics of the films annealed at 400 °C exhibited a high value of dielectric constant (~34). Further, frequency dependent C–V measurements showed a huge dispersion in accumulation capacitance due to the presence of TiO₂/Si interface states and dielectric polarization, was found to follow power law dependence on frequency (with exponent ‘s’=0.85). A low leakage current density of 3.6×10⁻⁷ A/cm² at 1 V was observed for the films annealed at 600 °C. The results of structure-electrical properties suggest that the deposition of titania by wet chemical method is more attractive and cost-effective for production of high-κ materials compared to other advanced deposition techniques such as sputtering, MBE, MOCVD and ALD. The results also suggest that the high value of dielectric constant ‘κ‘ obtained at low processing temperature expands its scope as a potential dielectric layer in MOS device technology.     

Structural and electrical properties of radio frequency magnetron sputtered tantalum oxide films: Influence of post-deposition annealing

The as-deposited and annealed radio frequency reactive magnetron sputtered tantalum oxide (Ta₂O₅) films were characterized by studying the chemical binding configuration, structural and electrical properties. X-ray photoelectron spectroscopy and X-ray diffraction analysis of the films elucidate that the film annealed at 673 K was stoichiometric with orthorhombic β-phase Ta₂O₅. The dielectric constant values of the tantalum oxide capacitors with the sandwich structure of Al/Ta₂O₅/Si were in the range from 14 to 26 depending on the post-deposition annealing temperature. The leakage current density was <20 nA cm^?2 at the gate bias voltage of 0.04 MV/cm for the annealed films. The electrical conduction mechanism observed in the films was Poole–Frenkel.     

Structural characterization of DC magnetron-sputtered TiO2 thin films using XRD and Raman scattering studies

Titanium dioxide films have been deposited using DC magnetron sputtering technique onto well-cleaned p-silicon substrates at an oxygen partial pressure of 7×10^–5 mbar and at a sputtering pressure (Ar+O₂) of 1×10^–3 mbar. The deposited films were calcinated at 673 and 773 K. The composition of the films as analyzed using Auger electron spectroscopy reveals the stoichiometry with an O and Ti ratio 2.08. The influence of post-deposition annealing at 673 and 773 K on the structural properties of the titanium dioxide thin films have been studied using XRD and Raman scattering. The structure of the films deposited at the ambient was found to be amorphous and the films annealed at temperature 673 K and above were crystalline with anatase structure. The lattice constants, grain size, microstrain and the dislocation density of the film are calculated and correlated with annealing temperature. The Raman scattering study was performed on the as-deposited and annealed samples and the existence of Raman active modes A_1g, B_1g and E_g corresponding to the Raman shifts are studied and reported. The improvement of crystallinity of the TiO₂ films was also studied using Raman scattering studies.     

Properties of CuAlO2 thin films deposited by polyacrylamide gel route

CuAlO₂ films were deposited on clean glass substrates by the acrylamide sol–gel dip coating technique. The coated films were dried in air oven for 30 min followed by heat treatment in air at different temperatures in the range of 350–500 °C. The films annealed at low temperatures exhibited weak x-ray diffraction (XRD) peaks. As the post anneal temperature increased beyond 375 °C, the XRD pattern exhibited the diffraction peaks of rhombohedral CuAlO₂. Surface morphology of the films indicated that the films annealed at low temperatures exhibit small grains. As the annealing temperature increases larger grains are observed. The root mean square (rms) value of the surface roughness increases with annealing temperature. The films exhibited optical transmission above 75%. The films post annealed at low temperature exhibited lower transmission. Optical band gap in the range of 3.43–3.75 eV was obtained for the films annealed at different temperature. Hall measurements indicated p-type conductivity. Resistivity of the films decreased from 25.0 to 2.0 Ω cm as the anneal temperature increased. Mobility and carrier density increased with annealing temperature.     

Strain evolution and dopant activation in P-lmplanted metastable pseudomorphic Si(100)/Ge0.12Si0.88

A metastable Ge_0.12Si_0.88 layer 265 nm thick was deposited pseudomorphically on a Si(100) substrate and then implanted with 100 keV phosphorus ions at room temperature for doses of 5 × 10¹³/cm² to 1.5 × 10¹⁵/cm². The ions stop within the epilayer (projected range ∼125 nm). MeV⁴He backscattering/channeling spectrometry, transmission electron microscopy, and double-crystal x-ray diffractometry were used to characterize the damage and strain in the films. The samples were subsequently annealed in high vacuum from 400-800°C for 30 min at each temperature. For the nonamorphized samples (doses of 5 and 10 × 10¹³/cm²), most of the implantation-induced damage and strain disappear after annealing at 400-550°C, but the implanted P ions activate poorly. After annealing at 700-800°C, near complete activation is achieved but the strain relaxes. For the amorphized samples (dose of 1.5 × 10¹⁵/cm²), the amorphous GeSi regrows by solid-phase epitaxy and the dopants are ∼100% activated after annealing at 550°C, but the regrown GeSi relaxes with a high density of dislocations. The strain relaxes more extensively upon annealing in an implanted sample than in a nonimplanted one, other conditions being equal. This effect is more pronounced at higher ion doses, probably due to the increased amount of damage introduced at high doses. On leave from Yonsei University, Seoul 120-749, Korea     

Deposition,post-deposition annealing,and characterization of epitaxial Ge films grown on Si(100) by pyrolysis of GeH4

As a first step towards developing heterostructures such as GaAs/Ge/Si entirely by chemical vapor deposition, Ge films have been deposited on (100) Si by the pyrolysis of GeH₄. The best films are grown at 700° C and are planar and specular, with RBS minimum channeling yields of ≈4.0% (near the theoretical value) and defect densities of 1.3 x 10⁸ cm⁻². Variations of in-situ cleaning conditions, which affect the nature of the Si substrate surface, greatly affect the ability to get good epitaxial growth at 700° C. The majority of the defects found in the Ge films are extrinsic stacking faults, formed by dissociation of misfit and thermal expansion accommodation dislocations. The stacking fault density is not significantly reduced by post-deposition annealing, as is the case for the dislocations observed in MBE Ge films. It is suggested that lowering the CVD growth temperature through the use of high vacuum deposition equipment would result in dislocation defects like those of MBE films which could then be annealed more effectively than stacking faults. Films with defect densities equivalent to MBE Ge films (~2 x 10⁷ cm⁻²) could then probably be produced.     

Annealing effects on physical properties of doped CdTe thin films for photovoltaic applications

Polycrystalline Cadmium Telluride (CdTe) thin films were prepared on glass substrates by thermal evaporation at the chamber ambient temperature and then annealed for an hour in vacuum ~1×10⁻⁵ mbar at 400 °C. These annealed thin films were doped with copper (Cu) via ion exchange by immersing these films in Cu (NO₃)₂ solution (1 g/1000 ml) for 20 min. Further these films were again annealed at different temperatures for better diffusion of dopant species. The physical properties of an as doped sample and samples annealed at different temperatures after doping were determined by using energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD), Raman spectroscopy, transmission spectra analysis, photoconductivity response and hot probe for conductivity type. The optical band gap of these thermally evaporated Cu doped CdTe thin films was determined from the transmission spectra and was found to be in the range 1.42–1.75 eV. The direct energy band gap was found annealing temperatures dependent. The absorption coefficient was >10⁴ cm⁻¹ for incident photons having energy greater than the band gap energy. Optical density was observed also dependent on postdoping annealing temperature. All samples were found having p-type conductivity. These films are strong potential candidates for photovoltaic applications like solar cells.     

Optical and electrical properties of nickel oxide thin films synthesized by sol–gel spin coating

Nickel oxide thin films were prepared by the sol–gel technique combined with spin coating onto glass substrates. The as-deposited films were pre-heated at 275 °C for 15 min and then annealed in air at different temperatures. The effects of the annealing temperature on the structural and optical properties of the films are studied. The results show that 600 °C is the optimum annealing temperature for preparation of NiO films with p-type conductivity and high optical transparency. Then, by using these optimized deposition parameters, NiO thin films of various thicknesses were deposited at the same experimental conditions and annealed under different atmospheres. Surface morphology of the films was investigated by atomic force microscopy. The surface morphology of the films varies with the annealing atmosphere. Optical transmission was studied by UV–vis spectrophotometer. The transmittance of films decreased as the thickness of films increased. The electrical resistivity, obtained by four-point probe measurements, was improved when NiO layers were annealed in N₂ atmosphere at 600 °C.