Kwang Soo Seol

Plasma-enhanced chemical vapor deposition and characterization of high-permittivity hafnium and zirconium silicate films

Deposition of hafnium silicate films with various hafnium contents was tried by plasma-enhanced chemical vapor deposition using tetraethoxysilane and a hafnium alkoxide. From x-ray photoelectron spectroscopy, the deposited films are confirmed to be silicate with Hf–O–Si bonds but without any Hf–Si bonds. The permittivity calculated from the capacitance of the accumulation layer increases monotonically with an increase in the hafnium content, whereas the optical band gap energy estimated from vacuum ultraviolet absorption spectra decreases. Similar results were obtained from zirconium silicate films deposited using tetraethoxysilane and a zirconium alkoxide. If we compare the films with the same hafnium or zirconium content, the hafnium silicate exhibits a higher permittivity and a larger band gap energy than the zirconium silicate.

Band-tail photoluminescence in hydrogenated amorphous silicon oxynitride and silicon nitride films

Photoluminescence (PL) measurements were performed on a series of hydrogenated amorphous silicon oxynitride and silicon nitride films with different nitrogen contents deposited by plasma-enhanced chemical-vapor deposition. From the PL and PL excitation spectra, the Urbach energy of the sample is found to be proportional to its PL half-maximum width, regardless of whether the sample is silicon oxynitride or silicon nitride. Time-resolved PL measurements showed that PL peak energy varies with time after the excitation, showing a systematic dependence on the chemical composition in the two materials. That the PLs observed in the two materials have very similar characteristics regardless of the presence of oxygen strongly indicates that the PLs result from the same chemical structure, more specifically Si–N bonds, and that the two materials have similar band-tail states associated with the static disorder. In the two materials, it is found that the electrons and holes photoexcited into such band-tail states r...

Effect of implanted ion species on the decay kinetics of 2.7 eV photoluminescence in thermal SiO2 films

Decay kinetics of photoluminescence (PL) existing around 2.7 eV has been studied in various ion‐implanted thermal SiO2 films as a function of implantation conditions. The PL observed in many samples shows decay constants shorter than 10 ms, which is a well‐observed decay constant for silica glass. The change in the decay constant and that in the PL intensity have been found to be systematically related with the mass and the dose of the implanted ions. Therefore, despite the short decay constant, the present 2.7 eV PL is attributable to a triplet‐to‐singlet transition of oxygen deficient centers, as in the case of silica glass. The rapid decay is interpreted as the increase in spin‐orbit coupling interaction due to structural deformations by ion implantation such as the formation of paramagnetic defects and/or densification.

Photoluminescence study on point defects in buried SiO2 film formed by implantation of oxygen

Defects in buried SiO2 films in Si formed by implantation of oxygen ions were characterized by photoluminescence (PL) excited by KrF (5.0 eV) excimer laser and synchrotron radiation. Two PL bands were observed at 4.3 and 2.7 eV. The 4.3 eV band has two PL excitation bands at 5.0 and 7.4 eV, and its decay time is 4.0 ns for the 5.0 eV excitation and 2.4 ns for the 7.4 eV excitation. The decay time of the 2.7 eV PL band is found to be 9.7 ms. These results are very similar to those for the 4.3 eV and the 2.7 eV PL bands, which are observed in bulk silica glass of an oxygen‐deficient type and attributed to the oxygen vacancy. Through the change in the PL intensity with the film thickness, the buried SiO2 film is considered to contain the oxygen vacancy defects in a high amount throughout the oxide.

Origin of photoluminescence around 2.6–2.9 eV in silicon oxynitride

A broad photoluminescence (PL) around 2.6–2.9 eV is known to appear in hydrogenated silicon oxynitride. Although its origin was reported to be Si–N bonds, it is not so clear since the material contains hydrogen. In the present research, we have confirmed that the same PL appears in silicon oxynitride grown by nitriding of silicon dioxide. The depth profile of the PL intensity agrees with that of the nitrogen concentration. Furthermore, the emission spectrum, excitation spectrum, and decay constant of this PL agree with those of the PL observed in silicon nitride. Based on these results and theoretical discussion, the origin of the 2.6–2.9 eV PL is estimated to be Si–N bonds.

Effects of ion implantation and thermal annealing on the photoluminescence in amorphous silicon nitride

When amorphous silicon nitride films are irradiated by a KrF excimer laser, they exhibit broad photoluminescence (PL) centered around 2.4 eV. The PL intensity gradually decreases and the PL peak energy shifts to a lower energy with an increase of the implanted dose of Ar+ ions. This means that the PL consists of two components with peak energies at 2.66 and 2.15 eV and that implantation-induced defects such as vacancies are not the PL centers. The PL intensity is found to decrease if the film was thermally annealed, while the decreased PL intensity of the ion-implanted film recovers by the thermal annealing. Based on these results, it is concluded that the defects generated by hydrogen release or bond breaking act as nonradiative recombination centers that quench the PL.

Photoluminescence of oxygen-deficient-type defects in a-SiO2

Abstract Oxygen-deficient-type defects in a-SiO 2 were studied by means of photoluminescence (PL) measurements. Various properties of the 4.4-eV PL such as the decay lifetime and the temperature dependence in oxygen-deficient-type a-SiO 2 can be explained in terms of an energy diagram involving two configurations of the oxygen-deficient-type defect. The 4.4-eV PL observed from the ion-implanted thermal oxides and the oxides prepared by the plasma-enhanced CVD method, has a stretched-exponential decay, suggesting a large structural distribution in the local network structures. A PL band at ∼ 1.8 eV associated with highly oxygen-deficit states is also observed in oxygen-deficient-type a-SiO 2 after high-dose γ-irradiation (dose: 10 MGy).

Synthesis of Size- and Structure-Controlled Ge2Sb2Te5 Nanoparticles

Pulsed laser ablation of Ge2Sb2Te5 target materials at approximately 400 Pa of ambient argon gas produces amorphous nanoparticles with a size distribution of from 4 to 30 nm. Thermal treatment of the nanoparticles in their aerosol states crystallizes the particles to both a hexagonal structure and a face-centered cubic structure at 300°C, while only a face-centered cubic structure results at 400°C. The crystallized nanoparticles were then size-classified by a differential mobility analyzer to produce size- and structure-controlled Ge2Sb2Te5 nanoparticles. The particles are revealed to consist of germanium, antimony and tellurium by composition analysis using energy dispersive X-ray spectroscopy.

Gas-phase production of monodisperse lead zirconate titanate nanoparticles

Laser ablative technology was used to prepare monodisperse nanoparticles (4–20 nm in diameter) of lead zirconate titanate (PZT). Laser ablation of a PZT ceramic target in oxygen ambience produced amorphous and irregularly shaped PZT nanoparticles. A subsequent on-line thermal treatment performed on the PZT nanoparticles dispersed in the gas phase brought about compaction and crystallization of the nanoparticles without additional particle growth. It was found that the amorphous nanoparticles began to crystallize above 600 °C, and they became a perovskite structure at 900 °C. The crystallized nanoparticles were then size classified by a differential mobility analyzer to yield monodisperse, highly pure, and single-crystalline PZT nanoparticles.

Visible electroluminescence in hydrogenated amorphous silicon oxynitride

The mechanism of electroluminescence in hydrogenated amorphous silicon oxynitride was investigated. The luminescence can be observed only in the samples with high nitrogen content and annealed at high temperatures. It depends on the direction of the applied electric field, and its peak photon energy decreases from 2.3 to 1.8 eV as the nitrogen content increases. From the measurements of conduction current and Fourier transform infrared absorption spectroscopy, it was found that the electrical conduction in the electric field region where the luminescence was observed is governed by the Poole–Frenkel process at the defect centers induced by the high temperature annealing. The electroluminescence is considered to be caused by electronic transition between the band-tail states, at least one of which is related to N or Si–N bonds.