Keiji Tsunetomo

Visible Photoluminescence from Si Microcrystals Embedded in SiO2 Glass Films

We report the observation of an efficient visible photoluminescence (PL) from Si microcrystals embedded in SiO2 glass films. The Si microcrystals were formed by the rf magnetron sputtering technique. The peak position of the PL spectra at 77 K shifts to a lower-energy side as the average diameter of the Si microcrystals increases.

Quantum Size Effect of Semiconductor Microcrystallites Doped in SiO2-Glass Thin Films Prepared by Rf-Sputtering

Semiconductors such as CdTe, CdSe and GaAs, microcrystallites could be successfully doped into SiO2-glass films by the magnetron rf-sputtering technique. The average size of the microcrystallites depended on sputtering conditions, and postannealing was not necessary to form microcrystallites in the silica-glass films. The average diameter varied from below 15 A to 62 A. In the optical absorption spectra, the absorption edge of the films clearly exhibited blue shift compared to each bulk semiconductor, and thus the quantum size effect could be found in these microcrystallites.

Preparation and Properties of Ge Microcrystals Embedded in SiO2 Glass Films

Ge microcrystals were successfully doped into SiO2 glass films by the rf magnetron sputtering technique. The dependence of the average size of Ge microcrystals on substrate temperature and annealing time was discussed. The optical absorption spectra of Ge microcrystals clearly exhibited the blue shift compared with a bulk Ge crystal, which seems to be due to a quantum size effect.

Preparation and Properties of Si Microcrystals Embedded in SiO2 Glass Films

Si microcrystals were successfully doped into SiO2 glass films by the rf magnetron sputtering technique. The dependence of the average size of Si microcrystals on substrate temperature was discussed with reference to transmission electron microscopy observations. The optical absorption spectra of Si microcrystals clearly exhibited the blue shift compared with a bulk Si crystal, which seems to be due to a quantum size effect.

Semiconducting CdTe Microcrystalline-Doped SiO2 Glass Thin Films Prepared by Rf-Sputtering

Semiconducting CdTe microcrystalline was successfully doped in SiO2 films by the magnetron rf-sputtering technique. The average size of the microcrystalline depended on the relative area and location of the CdTe chips on the target, as well as the postannealing time; and that of as-deposited films varied from 22 A to 62 A. From the optical absorption spectra, the absorption edge of the films clearly exhibited blue shifts compared to the bulk CdTe. Thus the quantum size effect could be found for these films.

Quantum size effect and HRTEM observation of CdSe microcrystallites doped into SiO2-glass films prepared by Rf-sputtering

CdSe microcrystallite-doped SiO2 glass films were prepared by the magnetron rf-sputtering technique. High resolution transmission electron microscopy (HRTEM) observation was carried out to determine the shape and the average size of the microcrystallites. The microcrystallites had a spherical configuration and they seemed to have a wurtzite structure. The optical band gap of the films clearly exhibited the blue shift compared to bulk CdSe. The shape of optical absorption spectra also changed as the microcrystallite size decreased. A simple model of the size quantization on interband absorption in a semiconductor sphere was used to explain the change of the optical absorption spectra. Taking into account the particle size distribution, the calculated absorption spectra successfully agreed with the real absorption spectra. The observed blue shifts of optical absorption were consistent with theoretical values calculated using the mean microcrystallite radii estimated from the HRTEM observations.

Structural Changes of Amorphous GeTe2 Films by Annealing (Formation of Metastable Crystalline GeTe2 Films)

Amorphous GeTe 2 films with the thickness ∼ 0.5 µm, prepared by sputtering technique, transform into the crystalline GeTe 2 films with the isomorphic structure to β-cristobalite, cubic SiO 2 , at T a (annealing temperature)=200°C. The cubic phase of GeTe 2 is metastable and decomposes into the mixed crystal of GeTe and Te at T a =250°C.

CuCl Microcrystallite-Doped SiO2 Glass Thin Films Prepared by RF Sputtering

CuCl microcrystallites were successfully doped into SiO2 glass thin films by means of the magnetron rf-sputtering technique. A transmission electron microscopy (TEM) measurement showed that the microcrystallites had a spherical configuration. The average size of the microcrystallites was less than 5 nm and it was affected by the preparation condition and postdeposition annealing time. Optical absorption peaks corresponding to Z3 and Z1,2 exciton were observed. These absorption lines shifted to a higher-energy side with decreasing microcrystallite size. This phenomenon seems to relate to the quantum size effect.

Preparation and Properties of InxGa1-xAs Microcrystallites Embedded in SiO2 Glass Films

InxGa1-xAs microcrystallites were successfully doped into SiO2 glass films by the rf-magnetron sputtering technique. These microcrystallites exhibited a variety of narrow band-gap structures which were affected not only by the quantum size effect but by the composition of these microcrystallites. The composition of the microcrystallite in these films depended on the sputtering target composition, and the average diameter of InxGa1-xAs microcrystallites estimated from X-ray diffraction spectra was controlled by the substrate temperature. The optical absorption spectra of these films clearly exhibited the shift of the absorption edge caused by the quantum size effect.

Stability of metastable GeTe2 in thin films

Amorphous GeTe 2 films prepared by the sputtering technique transform into metastable crystalline GeTe 2 films at T a (annealing temperature)=200 °C, and then decompose into the mixed phase of GeTe and Te crystals at higher T a . The crystal of GeTe 2 cannot be observed in the thicker film than 6 μm or in the self-supported film. The relative amount of crystalline GeTe 2 growing at T a =200 °C and the phase separation temperature decrease with film thickness increasing. From these facts, the stability of the crystalline GeTe 2 is closely related to the film thickness and existence of substrates.