Akira Kawabuchi

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.

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.

Evaluation of Epitaxial ZnTe Films Prepared by RF Sputtering by Means of Ion Beam Channeling

Epitaxial films of Zinc telluride are deposited by rf sputtering on the clean surface of GaAs(100), InP(100) and GaSb(100) substrates, which have lattice mismatches with ZnTe of 7.6, 3.8 and 0.1%, respectively. Ion-channeling measurements are carried out to evaluate the crystalline quality of the ZnTe films. The defect density in the films greatly depends on the lattice mismatch between ZnTe and the substrates. The epitaxial films with thicknesses of 130 to 150 nm on GaAs, InP and GaSb give minimum aligned yields Xmin of 32, 18 and 8%, respectively. The value of Xmin of the film on GaSb is fairly small, comparable to the value for the single crystal. The dependences of the dechanneling probability on the incident-beam energy indicate the presence of dislocation lines.

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.

Heteroepitaxial growth and optical properties of ZnSxTe1−x on GaAs(100) by RF sputtering

Ternary alloys ZnSxTe1−x (0<x<1) have been deposited epitaxially at a substrate temperature of 320 °C, by RF sputtering, on the clean surface of a GaAs(100) substrate. Raman spectra were measured for samples with various compositions x. The LO phonon bands in the alloy system have a modified two-mode behavior. Reflectance spectra of ZnSxTe1−x in the vacuum ultraviolet suggest a nonmonotonic dependence of the band structure on the composition.

Epitaxial growth of ZnTe on GaSb(100) by rf sputtering

Zinc telluride is deposited by rf sputtering on the clean surface of well lattice‐matched GaSb(100) substrates (with mismatch about 0.1%). The surface native oxides have been etched off by H2 plasma treatment at substrate temperatures of more than 220 °C. Reflection high‐energy electron diffraction patterns of ZnTe films prepared at 320 °C are streaked with (100) characteristics, which shows that the deposited layers are grown epitaxially. The crystalline quality of the ZnTe films which depends on the substrate temperature is evaluated by means of the optical reflectance. The peak height of the second‐derivative reflectance spectra, a measure of the crystalline quality, steeply increases at deposition temperatures of 270–320 °C. The deposition temperature of more than 320 °C is needed for high crystalline quality. Moreover, the film prepared at 370 °C on GaSb gives a minimum aligned yield χmin of 8% in ion beam channeling experiments of Rutherford backscattering spectrometry.

Heteroepitaxial Growth of ZnSxTe1-x on GaAs(100) by RF Sputtering

Ternary alloys ZnSxTe1-x(0<x<1) are deposited epitaxially at a substrate temperature of 320°C by rf sputtering on the clean surface of a GaAs(100) substrate from which the surface native oxides have been etched off in advance by H2 plasma treatment. The alloy film at x=0.62 shows the best crystalline quality in terms of RHEED patterns with little lattice mismatch with GaAs.

Epitaxial growth of ZnTe on GaAs(100) by RF sputtering

Cadmium telluride is deposited by rf sputtering on the clean surface of GaAs(100) substrates from which the surface native oxides have been etched off in advance by H2 plasma treatment. RHEED patterns of CdTe films prepared at 270°C on GaAs pretreated with H2 plasma at 120°C are streaked with (100) characteristics, which shows that the deposited layers are grown epitaxially. The crystalline quality of the CdTe films, which depends on the substrate temperature, is evaluated by means of the optical reflectance. The peak height of the second-derivative reflectance spectra, which is a measure of the crystalline quality, steeply increases at deposition temperatures of 220~270°C. Thus a deposition temperatures of more than 270°C is needed for high crystalline quality.