Yoji Tokumitsu

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.

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.

Study of the Surface of CdTe Treated in H2 Plasma

The surface of CdTe can be cleaned using H2 plasma. Native oxide and thin Te layers on the CdTe surface are removed at a temperature higher than 100°C. The photoluminescence intensity of edge emission became largest as the surface of CdTe was treated in H2 plasma at a temperature of about 100°C. From the intensity of the defect-related emission band in photoluminescence spectra of H2-treated films, it is concluded that the surface treatment of CdTe by H2 plasma at 170°C is most appropriate.

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 CdTe by H2 Sputtering

CdTe films can be grown epitaxially on InSb(100) by chemical sputtering in H2. The crystalline quality of the epitaxial layers is improved when the substrate temperatures are in the range of 200 to 250°C at a high rf discharge power of 400 W. In channeling experiments employing Rutherford backscattering spectrometry, the χmin (aligned yield/random yield) in the film prepared at 270°C and 400 W is 9.5%. A lattice strain of 0.05% is obtained from the results of X-ray diffraction. These values show that the crystalline quality of the epitaxial film grown by H2 sputtering is superior to the film grown by Ar sputtering.

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.