Mizunori Ezaki

Characterization of Nd:Y3Al5O12 thin films grown on various substrates by pulsed laser deposition

Epitaxial Nd‐doped yttrium aluminum garnet (NdxY3−xAl5O12 or Nd:YAG) films have been grown on various substrates by pulsed laser deposition for the purpose of fabricating diode‐pumped waveguide lasers. The films were characterized by Rutherford backscattering, x‐ray diffraction, atomic force microscopy, and photoluminescence measurements. Nd:YAG films on (100) silicon substrate with a large lattice mismatch show oriented stoichiometric growth. On the other hand, Nd:YAG films on garnet substrates (Nd undoped Gd3Ga5O12,Y3Al5O12 and Zr‐, Sc‐doped Gd3Ga5O12) show epitaxial growth with smooth surfaces. The optical properties of Nd‐doped YAG thin films on various substrates were comparable to those of Nd:YAG bulk laser crystal.

Surface modification of III-V compound semiconductors using surface electromagnetic wave etching induced by ultraviolet lasers

The surface modification of semiconductors by laser-induced surface electromagnetic wave (SEW) etching was investigated. With the novel etching method using a holographic exposure system, submicron periodic dot structures were fabricated directly on semiconductor substrates (n-InP, n-GaAs, and InGaAs-InP). Making use of laser polarization dependence in this etching system, a variety of surface modifications could be achieved on the semiconductors. In particular, in the case of using the s-polarization light, periodic submicron dot structures with a geometrical diameter down to 80 nm could be obtained directly using a single-step process without a mask. The InGaAs-InP dot structures were studied optically by means of photoluminescence spectroscopy, and the blue shift of the photoluminescence energy up to 5.36 meV was observed for the smallest dots, which displayed a lateral quantization. >

Crystal growth of Nd:YAG laser films on various substrates by pulsed laser deposition

Fabrication of textured Nd doped yttrium aluminum garnet ( Y3Al5O12, YAG) crystalline thin films on Si and MgO single-crystal substrates by the pulsed laser deposition technique has been demonstrated for the first time. The films were characterized by means of Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). The results indicate that the composition of these films is the same as that of YAG doped with Nd (8.3 at.%), and the AFM image shows that the submicron Nd:YAG crystallites were oriented on the silicon surface at the substrate temperature of 700° C. The formation of these submicron crystallites was observed on the surface of Nd:YAG films grown on substrates having a large lattice mismatch with Nd:YAG.

Periodic submicrometer dot structures on n‐GaAs substrates fabricated by laser‐induced surface electromagnetic wave etching

Periodic submicrometer dot structures were fabricated by laser‐induced surface electromagnetic wave (SEW) etching of n‐GaAs substrates using the holographic exposure system of the frequency‐tripled Nd:YAG laser. The shorter and longer diameters were about 310 and 540 nm, respectively. Spatial periods along two perpendicular axes were 370 and 545 nm, respectively. These periods were nearly in agreement with the calculation. The period of SEW grating depended on not only the laser wavelength, but also the number density of the laser‐induced quasifree carriers.

Epitaxial growth of Nd:YAG thin films by pulsed laser deposition

Abstract Epitaxial growth of Nd:Y3Al5O12 (Nd:YAG) films on SGGG (Zr- and Sc-doped Gd3Ga5O12) and YAG substrates by pulsed laser deposition using a KrF excimer laser at substrate temperatures of 800°C to 910°C was investigated. The composition of the films was investigated by Rutherford backscattering spectroscopy and the crystallinity by X-ray diffraction analysis. The optical properties of Nd:YAG thin films were investigated by photoluminescence (PL) measurements. The PL spectrum of the Nd:YAG film on the YAG substrate exhibited 4 F 3/2 → 4 I 9/2 and 4 F 3/2 → 4 I 11/2 transitions of Nd3+ ions in YAG which were almost the same as those of the Nd:YAG bulk crystal.

Dot structures fabricated by laser etching : laser wavelength dependence of dot structures fabricated by laser etching

Submicron periodic dot structures on semiconductor substrates (n-InP, n-GaAs) were fabricated directly with the one-step laser-photochemical dry etching of n-InP and n-GaAs using a holographic exposure system. We employed a new etching technique which makes use of laser-induced surface electromagnetic waves (SEW) in the etching gas/semiconductor interface. The size of dot structures on n-InP was about 105 nm for the frequency-tripled Nd:YAG laser and 80 nm for the frequency-quadrupled Nd:YAG laser. Thus, the size of dot structures depended upon the incident laser wavelength.

Fabrication of Periodic Submicron Dot Structures of N-InP by Laser-Induced Surface Electromagnetic Wave Etching

Periodic submicron dot structures were fabricated by laser-induced surface electromagnetic wave etching of indium phosphide substrates. The shape of the dot was observed as a cone whose diameter at the half maximum was about 0.2 µm. Periods along two perpendicular axes were 0.38 µm and 0.57 µm, respectively. The periods were nearly in agreement with the calculation.

Spatial controllability of periodic ripple structures generated in laser etching of n-GaAs

Spatial controllability of periodic ripple structures was investigated in laser etching of n-GaAs. For single-beam etching and holographic etching with high ratios of average spacing of holographic grating to average spacing of ripple structures (Λh/Λh), ripple structures were observed. In particular, in p-polarization, spatial fluctuation was greater than that in s-polarization. This might occur because phase distortion cannot be eliminated by p-polarization beam irradiation. For holographic etching with small Λh/Λr ratios, ripple structures were changed into grating structures because these grating structures might be generated in phase with holographic gratings.

Delineation performances of advanced 100-kV EB writer on x-ray membrane mask

The keys to precision x-ray mask fabrication are the EB mask writer and the process of writing on a thin membrane. This paper concerns the delineation performance for 100 kV EB writing on x-ray membrane mask. We installed and evaluated an advanced EB mask writer, the EB-X3, which features an accelerating voltage of 100 kV and a 5-axes laser interferometer stage employing a laser measurement system with a resolution of 0.6 nm for high resolution and accuracy. The stable 100 kV EB has a good resolution around 50 nm and a beam address of 1 nm, which provide a repeatability of mark detection within 4 nm. As a result, an absolute image placement accuracy within 15 nm was obtained for 1G-bit level ULSI patterns. In addition, the combination of 100 kV EB and membrane process was found to reduce proximity effects. By several improvements including higher-order height correction and membrane process refinement, the final target of an absolute image placement error within 10 nm and a CD accuracy within 8 nm should be achieved in FY2000.

Surface modification of semiconductors by laser-induced surface electromagnetic wave etching

The surface modification of semiconductors by laser-induced surface electromagnetic wave etching was investigated. With the novel etching method using a holographic exposure system, submicron periodic dot structures were fabricated directly on semiconductor substrates (n-InP, n-GaAs). Making the best of laser polarization dependence in this etching system, a variety of surface modification could be obtained on the surface of InP and GaAs. Especially, in the case of using s-polarization laser lights, periodic submicron dot structure could be fabricated directly with a single step process without any mask process. The size of dots by the etching depended on the incident laser wavelength, and the smallest size of dots was 80 nm. The exponential growth of the SEW grating with the positive gain was demonstrated experimentally. As the etched depth of the SEW grating approached to the laser wavelength, the saturation of the growth due to self-limiting effect was also demonstrated experimentally for the first time.