Shunsuke Ohtsuka

Nonlinear optical property of CdTe microcrystallites doped glasses fabricated by laser evaporation method

Samples of CdTe microcrystallites doped glasses were fabricated by a high energy pulsed laser evaporation method. In order to fabricate a CdTe doped glass, synthesis of CdTe microcrystallites and formation of SiO2 films were carried out alternately on a fused silica glass substrate. The absorption edge of the CdTe doped glasses shifted to a higher energy region than that of the bulk CdTe due to the quantum size effect as the particle size of CdTe microcrystallites decreased. The third‐order nonlinear susceptibility of χ(3) was estimated to be 4×10−7 esu at 580 nm using the method of degenerate four wave mixing.

Fabrication of microcrystallites of II–IV compound semiconductors by laser ablation method

Abstract Microcrystallites of CdTe and CdS were obtained by pulsed laser ablation in argon gas. Average particle size depended on laser power, and on gas pressure during ablation. Particle diameter of CdTe could be controlled from 4 to 10 nm and their particles dispersed in methanol showed a quantum size effect on measurements of absorption property. Photoluminescence spectra of microcrystallites of CdS had a strong band edge emission related to impurities or defects. We confirmed that the laser ablation method to fabricate microcrystallites of II-VI compound semiconductors was useful.

Ultrafast nonlinear optical effect in CdTe-doped glasses fabricated by the laser evaporation method

Abstract The laser evaporation method is an attractive technology to synthesize composite materials. We tried to apply the laser evaporation method on fabrication of CdTe-doped glasses for the first time. CdTe microcrystallites embedded in SiO2 films were confirmed by transmission electron microscope images. The third-order nonlinear susceptibility χ(3) and the decay time τ of CdTe-doped glasses were measured by three-beam forward type degenerate four-wave mixing. The maximum value of χ(3) was estimated 4.2 x 10-7 esu when the absorption coefficient was 6000 cm-1. From the limitation of pulse duration of 5 ps, τ was not exactly measured but imagined to be shorter than 10 ps, which was much faster than the other semiconductor-doped glasses ever reported. The figure of merit defined as χ(3)/ατ is probably larger than 7.

Improvement of fabrication technique for CdTe microcrystallite-doped glass films

Abstract Thin films of CdTe microcrystallite-doped were successfully fabricated using an improved technique based on a laser evaporation (LE) process. In this technique, the microcrystallites were fabricated by a LE method and the glass matrix was fabricated by a plasma enhanced chemical vapour deposition (PECVD) method instead of a LE method. Furthermore, the size-distribution of CdTe microcrystallites was controlled by changing the substrate position during the LE process. The film fabricated using the improved technique had a smooth surface and narrow size-distribution compared with films fabricated by the former method in which both of microcrystallites and glass matrix were fabricated by a LE method. Because of these features, effective optical nonlinearity of the present sample was about 3–4 times as large as that of the former samples.

Fabrication of glass-capsuled CdTe microcrystals using laser evaporation and plasma chemical vapour deposition method

CdTe microcrystals encapsulated in a silica glass layer were successfully fabricated. Spherical CdTe microcrystals were prepared by laser evaporation of a CdTe target in an argon gas atmosphere. The ensuing microcrystals plus argon gas passed through a tetramethoxysilane (TMOS)+O2 plasma in which they were encapsulated in an amorphous layer, 2–2.5 nm thick. Characteristic X-rays from the surface layer were measured using an energy dispersive X-ray spectrometer equipped in a high-resolution transmission electron microscope. Measurements indicated that the glass layer consisted of silicon and oxygen, with no cadmium or tellurium included. The CdTe microcrystals fabricated with our laser evaporation system showed two specific kinds of particle: small particles (below 10 nm) and large ones (over 100 nm). Using precise electron-beam diffraction testing, we concluded that the large microcrystal is a single crystal with a hexagonal structure. The deposition rates and infrared transmission of silica glass prepared by TMOS or tetraethoxysilane plasma-enhanced chemical vapour deposition are also discussed. The highest deposition rate, 30 nm s−1, of silica glass can be achieved in the centre of the plasma when the input r.f. power is 150 W.