Scandium Oxide Films Research Articles

Relationship between Oxygen Defects and Properties of Scandium Oxide Films Prepared by Ion-Beam Sputtering

Scandium oxide (Sc2O3) thin films with different numbers of oxygen defects were prepared by ion-beam sputtering under different oxygen flow rates. The results showed that the oxygen defects heavily affected crystal phases, optical properties, laser-induced damage threshold (LIDT) and surface quality of Sc2O3 films. The thin film under 0 standard-state cubic centimeter per minute (sccm) oxygen flow rate had the largest number of oxygen defects, which resulted in the lowest transmittance, LIDT and the worst surface quality. In addition, the refractive index of 0 sccm Sc2O3 film could not be measured in the same way. When the oxygen flow rate was 15 sccm, the Sc2O3 film possessed the best transmittance, refractive index, LIDT and surface roughness due to the lowest number of oxygen defects. This work elucidated the relationship between oxygen defects and properties of Sc2O3 films. Controlling oxygen flow rate was an important step of limiting the number of oxygen defects, which is of great significance for industrial production.

Effect of Annealing on Optical, Mechanical, Electrical Properties and Structure of Scandium Oxide Films

Scandium oxide (Sc2O3) films are deposited by reactive magnetron sputtering. The effects of annealing on the structure, as well as the optical, mechanical, and electrical properties are investigated. The detailed investigation of the mechanical properties and high load indentation resistance in combination with electrical and optical properties is done. It is noted that after annealing at 300 °C, the extinction coefficient and refractive index slightly decreases. It is reported that before and after annealing, Sc2O3 films with cubic phase remains very hard (19 GPa) and resistant to high load (up to 1N) indentation test. Moreover, the effects of post‐deposition annealing on electrical characteristics of metal–insulator–semiconductor (MIS) structures with Sc2O3 gate dielectric layer are investigated. After the annealing procedure, the MIS structures are characterized by lower frequency dispersion, lower flat‐band voltage value, and lower effective charge density. The insulating properties remain at similar level when compared with the devices fabricated with as‐deposited dielectric material. The findings that are in this study make the investigated Sc2O3 films a promising material for various applications in optics, optoelectronic, and electronic semiconductor structures.

Optical properties and charge transport of textured Sc2O3 thin films obtained by atomic layer deposition

Scandium oxide films with thickness d = 20–100 nm were deposited by atomic layer deposition (ALD) using tris(methylcyclopentadienyl) scandium (III) Sc(MeCp)3 and water vapors as precursors at reactor temperature range of 200–400 °C. The ALD-window was detected in the range of 230–370 °C. Growth per cycle remained constant and was 0.080–0.084 nm/cycle in this range. O/Sc ratio was found to be 1.49 which is close to stoichiometric Sc2O3. The films were polycrystalline. The grains were more apparent for the films grown at higher temperatures. The grain size increased with thickness. Cubic Sc2O3 phase was determined by FTIR, Raman spectroscopy and X-rays diffraction.In general, different crystallographic directions are more preferential for different process conditions. Films were textured and their growth occurred mainly in the (400) direction. The refractive index dispersions of deposited films were well described by the Cauchy model. Optical properties depended weakly on process parameters (temperature or thickness). As it was detected for the films with close thickness the refractive index slightly increased with deposition temperature increase. The Nasyrov-Gritsenko (N-G) multiphonon trap ionization model well describes the charge transport. The trap parameters were determined to be: concentration N = 1.5 × 1019 cm−3, thermal energy Wt = 0.83 eV, and optical energy Wopt = 1.66 eV.

Mechanistic study of the atomic layer deposition of scandium oxide films using Sc(MeCp)2(Me2pz) and ozone

The atomic layer deposition (ALD) of scandium oxide (Sc2O3) thin films is investigated using Sc(MeCp)2(Me2pz) (1, MeCp = methylcyclopentadienyl, Me2pz = 3,5-dimethylpyrazolate) and ozone on hydroxyl-terminated oxidized Si(111) substrates at 225 and 275 °C. In situ Fourier transform infrared spectroscopy reveals that 1 not only reacts with surface hydroxyl groups at 275 °C, as expected but also with the SiO2 layer, as evidenced by losses in the SiO2 longitudinal optical and transverse optical phonon modes, resulting in the partial transformation of near-surface SiO2 to an ScSixOy interface layer. Ozone then combusts the MeCp groups of the O–Sc(MeCp)2 chemisorbed species, yielding surface carbonates, and oxidizes some of the underlying silicon, evidenced by gains in the SiO2 phonon modes. The Me2pz group from the next pulse of 1 reacts with these surface carbonates, leading to Sc–O–Sc bond formation (Sc2O3 deposition) and the restoration of an O–Sc(MeCp)2 surface. The reaction of the SiO2 substrate with 1 and the oxidation of silicon by ozone are temperature-dependent processes that occur during the initial cycles of film growth and directly impact the changes in the intensities of the SiO2 phonon modes. For instance, the intensity of the net gains in the phonon modes following ozone exposure is greater at 275 °C than at 225 °C. As the ALD cycle is repeated, the formation of an ScSixOy interface layer and deposition of an Sc2O3 film result in the gradual attenuation of the reaction of the SiO2 substrate with 1 and the oxidation of the underlying silicon by ozone. In addition to the ALD process, characterized by ligand exchange and self-limiting reactions, there are gas-phase reactions between 1 and residual water vapor near the substrate surface that lead to deposition of additional Sc2O3 and surface carbonates, the extent of which are also dependent on the temperature of the substrate. After 20 cycles of 1/ozone, the film thicknesses derived from ex situ X-ray photoelectron spectroscopy measurements are 2.18 nm (225 °C) and 3.88 nm (275 °C). This work constitutes the first mechanistic study of an Sc2O3 ALD process using ozone as the oxidant and emphasizes the significance of atypical reactions between the substrate and the reactants that influence the growth rate and near-surface stoichiometry during the initial cycles of film deposition.

Correlation between stoichiometry and properties of scandium oxide films prepared by reactive magnetron sputtering

Scandium oxide films were deposited on fused silica substrates by reactive pulsed DC magnetron sputtering. The use of feed-back optical emission monitoring enabled high-rate reactive deposition of films with tunable stoichiometry and properties. The under-stoichiometric, stoichiometric and over-stoichiometric scandium oxide films were prepared. The compressive stress in films was between 235 and 530MPa. We showed that phase structure, density, surface roughness and optical properties of the scandium oxide are affected by the film stoichiometry and deposition conditions. Transparent scandium oxide films were slightly hydrophobic (94±3°), homogeneous with a crystallite size of 20±5nm. The lowest extinction coefficient 0.7×10−3, the highest refractive index 2.08 (both quantities at the wavelength of 355nm) and the highest density 4.1±0.1g cm−3 exhibited film prepared with the stoichiometric composition. Stoichiometric scandium oxide can be used in various optical applications as high refractive index and wide bandgap material. Transitions to under- or over-stoichiometry lead to a decrease of film density, refractive index and increase of the extinction coefficient.

Nitridation of Si by N2 Electron Cyclotron Resonance Plasma and Integration with ScOx Deposition

Nitridation of silicon was achieved by exposure of silicon to electron cyclotron resonance plasma. The growth rate decreased as the nitridation time increased due to the growth process being limited by the diffusion of nitrogen through the growing layer. The thickness of the layer was about 1.5 nm for a nitridation time of 30 s, according to ellipsometry and transmission electron microscopy measurements. Additionally, scandium oxide films were deposited by high pressure sputtering on top of the nitrided silicon, as well as in reference un-nitrided silicon, to study the influence of the nitridation process on the interface properties. The silicon nitride layer is efficient in preventing the growth of interfacial silicon oxide. The minimum of the density of interface traps for structures with 30 s nitridation was around , indicating an improvement with respect to the deposition on un-nitrided silicon with of about . The best interface quality was obtained for the shortest nitridation time of 30 s. Finally, it was observed that the nitridation process greatly inhibits interface reaction during rapid thermal annealing at .

Structure of Sc2O3 films epitaxially grown on α-Al2O3 (0001)

The crystal structure of scandium oxide films epitaxially grown on α-Al2O3 (0001) under an ultrahigh-vacuum is studied by single-crystal x-ray diffraction. The Sc2O3 film grows in bixbyite phase on the basal (0001) surface of the sapphire substrate with its ⟨111⟩ axis aligned parallel to the substrate normal. In-plane orientation of the film, however, exhibits two distinct growth directions that are defined by the two possible surface orientations of the stepped α-Al2O3 substrate. The atomic structure of the high-quality epitaxial film is fully relaxed and the film has unusual thickness uniformity.

Optical properties of scandium oxide films prepared by electron beam evaporation

Scandium oxide films were prepared by electron beam evaporation. The effects of substrate temperature and oxygen partial pressure on the microstructure and optical properties of the films were investigated. Films deposited at 300 °C were crystalline, whereas those deposited on unheated substrates were essentially amorphous. Normal-incidence transmittance spectra of the films revealed that the films were optically inhomogeneous. A model based on an inhomogeneous layer was applied to extract the refractive index from the transmittance spectra. It was found that the refractive index increased with the substrate temperature and decreased with the introduction of oxygen.

Scandium oxide antireflection coatings for superluminescent LEDs

For an employment of laser diodes as superluminescent LEDs (SLDs) or amplifiers, the facets of the diodes must be coated with antireflection films. In the work reported, scandium oxide was evaporated from an e-beam source onto Supersil II fused silica substrates. The obtained samples were used for measurements of absorption and reflectivity. Results of index measurements on e-beam evaporated films are presented. It is shown that excellent coatings with reflectivities of 0.00025 can be obtained using these films. Attention is given to the refractive indices for scandium oxide films as a function of wavelength, the power output vs current for laser before coating and after coating with Sc2O3.