Kenichi Kondo

Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS2.: I. Absorption Spectra of CuFeS2 and Fe-Doped CuAlS2 and CuGaS2

Optical absorptions have been measured in chalcopyrite, CuFeS 2 , and Fe-doped CuAlS 2 and CuGaS 2 . An extra absorption band with two peaks is observed at the low energy region of the absorption edge for Fe-doped CuAlS 2 and CuGaS 2 .Energy positions of two absorption peaks are 1.3 eV and 2.0 eV for CuAlS 2 and 1.2 eV and 1.9 eV for CuGaS 2 , respectively. The intensity of this absorption band increases with the increase of doped Fe ions and grows into the absorption edge of CuFeS 2 . Its oscillator strength comes up to 7·10 -2 . In chalcopyrite photoconductivity is observed and its maximum is just at the same energy region of the absorption edge. By comparing our results with those of absorption measurements for Cu- or Fe-doped ZnS it is concluded that this absorption band originates from the charge transfer transitions relating to 3d electron of Fe ions and the absorption edge of CuFeS 2 rises from the band-to-band transition corresponding to this charge transfer transition.

Deposition of low-resistivity ITO on plastic substrates by DC arc-discharge ion plating

Low-resistivity SnO 2 doped In 2 O 3 (ITO) transparent conductive films were successfully deposited on SiO 2 -coated plastic substrates using d.c. arc-discharge ion plating. A resistivity of 2.45 × 10 -4 Ω cm was achieved at a substrate temperature of 100 °C. The films had a polycrystalline structure with a [111] preferred orientation and the strongest peak was at (222). The average grain size of the films was approximately 500 nm. The visible transparency of the films was approximately 80%, and no deformation of the substrate was observed.

Growth of CuInS2 films by rf ion plating and their characterization

Abstract Films of the chalcopyrite semiconductor CuInS2 were grown by rf ion plating at low substrate temperature of 400°C for various levels of substrate bias, ranging from + 50 to − 50 V. The Cu and In compositions were controlled by varying the electron beam power of the Cu2S and In2S3 sources. The crystalline quality was influenced by the level of the substrate bias. There were significant differences in surface morphology and crystallinity between films prepared under either negatively biased or floating conditions and those prepared under either positively biased or grounded conditions. Single-phase CuInS2 films of the best quality were obtained when the substrate was subjected to the floating condition. Such substrate bias dependence of crystalline quality clearly demonstrates the critical role that ions play in films prepared at low temperature.

Nozzle diameter effects on CuInSe2 films grown by ionized cluster beam deposition

Abstract Thin films of the chalcopyrite semiconductor CuInSe2 were grown by an ionized cluster beam (ICB) deposition technique at a low substrate temperature of 300°C. We studied the effect of nozzle diameter (a perforation on the top lid of the crucibles) of the cluster-source crucibles on the thin films. The diameters were 1.7, 2.0, or 3.0 mm. The deposited films obtained were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning ion mass spectroscopy (SIMS), and Raman spectroscopy. Change in the nozzle diameter significantly affected both the intensity of the Raman peaks at 183 and 260 cm−1 and the crystallinity of the CuInSe2 films. The maximum diameter for obtaining good crystallinity of CuInSe2 films is between 2.0 and 3.0 mm. It is found that the energy of Cu clusters plays a very important role in the crystal growth of CuInSe2.

Low Symmetry Crystal Field Splitting of 4T1 States of Co2+ in CuGaS2

The optical absorption spectra of CuGaS 2 :Co are observed at a room temperature and at 2 K in near infrared and visible regions, the low energy side of the absorption edge (20,000 cm -1 ) of the host crystal. The spectra show a broad band in the vicinity of 7,000 cm -1 and a fine structured band around 13,000 cm -1 . The fine structure of the upper band is analyzed by calculating the energy level scheme taking account of a low symmetry ( D 2 d ) crystal field and the spin-orbit coupling in addition to the cubic ( T d ) field. A reasonable choice of the parameters reproduces the observed spectra fairly well and give the g -shifts and zero field splitting constant which agree quite well with the observed values by Kaufmann et al. (Solid State Commun. 15 (1974) 1881).

Polycrystalline silicon thin films grown by dc arc discharge ion plating

Polycrystalline silicon thin films were produced with a high deposition rate of over 10 A/s at a low temperature of 300°C using a dc arc discharge ion plating method, where the plasma density was 1012 cm−3 and the source material was solid silicon. The crystalline volume fraction (deduced from a Raman scattering) could be controlled between 0 and 80% by adjusting the process pressure (10 and 70 mTorr, respectively), which was the total pressure of the reactive gas (hydrogen) and discharge gas (argon) in the deposition chamber. Furthermore, increase of the partial pressure of hydrogen also increased the crystalline fraction of the film. These results suggest that highly concentrated active hydrogen plays an important role in the growth of polycrystalline silicon films.