Masaya Ichimura

Electrochemical deposition of SnS thin films

Abstract SnS has a bandgap around 1.0–1.3 eV and the p-type conductivity, and therefore is suitable for the absorption layer in solar cells. In this study, Sn was deposited onto In2O3-coated glass substrates by electrochemical deposition from aqueous solutions and characterized chemically, structurally, and optically. The deposition bath contained SnSO4 and Na2S2O3. The deposited SnS was polycrystalline and of orthorhombic structure, and its composition was slightly Sn-rich. The direct bandgap was estimated to be 1.3 eV from optical transmission spectra. The relationship between the film properties and the deposition parameters was investigated to optimize the deposition condition.

Structural and optical characterization of CdS films grown by photochemical deposition

CdS thin films are grown by photochemical deposition from an aqueous solution and characterized by x-ray diffraction (XRD), Raman spectroscopy, photoluminescence measurement, and optical transmission spectroscopy. The films are deposited at room temperature and annealed at temperatures up to 500 °C. The as-deposited film is dominantly zinc blende cubic. The cubic phase remains dominant until the annealing temperature becomes higher than 400 °C. By the annealing at 450 °C, the XRD pattern turns to that of hexagonal phase. Moreover, its peak width decreases and the near-band-edge luminescence begins to be observed. The band gap is decreased by annealing below 400 °C and then abruptly increased by the annealing at 450 °C. This annealing behavior of the band gap is interpreted considering the quantum size effects, the band tail due to disorder, and the cubic-hexagonal transition.

Photochemical deposition of ZnSe polycrystalline thin films and their characterization

Abstract ZnSe thin films were deposited for the first time by an alternative, recently established novel technique, namely ‘photochemical deposition’, from an aqueous solution. The various deposition parameters and post-deposition treatment conditions were optimized for the growth of stoichiometric, uniform ZnSe thin films on indium-tin-oxide coated glass substrate. The as-deposited films were annealed at 300 and 400 °C and both the as-grown and annealed films were characterized by various techniques such as X-ray diffraction (XRD), Raman spectroscopy, Auger electron spectroscopy (AES) etc. The XRD study confirmed the formation of cubic ZnSe upon annealing at 300 °C. The optical phonon peak corresponding to crystalline ZnSe was clearly observed in the Raman spectrum, which additionally confirmed the deposition of ZnSe compound semiconductor. AES analysis indicated that, the prepared ZnSe films exhibit stoichiometric composition.

A New Technique of Compound Semiconductor Deposition from an Aqueous Solution by Photochemical Reactions.

CdS films were successfully formed on a glass substrate in an aqueous solution containing S2O32- and Cd2+ ions by photochemical reaction. S2O32- ions in the growth solution absorb ultra-violet light of wavelengths shorter than about 300 nm, and the excited S2O32- ions supply sulfur atoms and electrons to the metal ions such as Cd2+. Thus, the formation reaction of the sulfide semiconductor occurs in the only illuminated region. Photochemically deposited CdS thin films were polycrystalline of hexagonal structure. The composition of the films became stoichiometric by the annealing at temperatures higher than 300° C.

Native defects in the AlxGa1−xSb alloy semiconductor

Defect concentrations in AlxGa1−xSb which is in equilibrium with a liquid phase are calculated. When the liquid phase is Ga rich, a Ga antisite (Ga2−Sb) or an Al antisite (Al2−Sb) is dominant, and the concentrations of vacancies are much smaller than the antisite concentrations. Ga2−Sb is dominant in GaSb equilibrated with a Sb‐rich solution, but the concentration of Sb antisites comes close to that of Ga2−Sb as temperature is lowered. For x larger than 0.6, a group‐III vacancy is the predominant defect in the case of Sb‐rich solutions. Calculated net acceptor concentrations agree well with those determined experimentally. A complex defect composed of GaSb and a Ga vacancy, which have been taken as the dominant residual acceptor, is expected to be negligible.

Synthesis, crystal growth and FTIR, NMR, SHG studies of 4-methoxy benzaldehyde-N-methyl-4-stilbazolium tosylate (MBST)

A novel organic nonlinear optical material 4-methoxy benzaldehyde-N-methyl-4-stilbazolium tosylate has been synthesized and good optical quality crystals were grown by slow cooling solution growth technique. Powder X-ray diffraction studies have been carried out and the lattice parameters were calculated. FTIR spectra were recorded to identify the various functional groups present in the crystal. NMR spectrum studies have also been done. The powder second harmonic generation studies were done with Kurtz powder technique and the results were compared with urea.

SnS thin films fabricated by pulsed and normal electrochemical deposition

Abstract SnS thin films were deposited onto Sn-doped In2O3-coated glass substrates by pulsed and normal electrochemical deposition (ECD) from aqueous solutions containing SnSO4 and Na2S2O3. Deposited SnS was polycrystalline and had orthorhombic structure, and its composition was S-rich. The films deposited by pulsed ECD were much denser and had smaller surface roughness than the films deposited by normal ECD.

Photochemical deposition of Se and CdSe films from aqueous solutions

Abstract Elemental Se and CdSe were successfully deposited by the photochemical deposition (PCD) technique. The substrate was held in an aqueous solution and was irradiated with a mercury lamp. The deposition solution for Se contained Na2SeO3 and Na2SO3. The deposited films were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The deposited elemental Se was amorphous and crystallized by annealing at 200°C. A CdSe film was also deposited from a solution containing Cd2+ ions. Its composition was almost stoichiometric. In those PCD processes, sulfite ions acted as a reductant under UV irradiation.

Experimental determination of band offsets at the SnS/CdS and SnS/InSxOy heterojunctions

The semidirect x-ray photoelectron spectroscopy technique was used to measure the band alignments at the interface of heterostructures based on SnS. The layers were deposited by electrochemical deposition (ECD), chemical bath deposition (CBD), or photochemical deposition (PCD). The following four kinds of heterojunctions were characterized. (1) ECD-SnS/PCD-CdS. (2) CBD-SnS/PCD-CdS. (3) ECD-SnS/ECD-InSxOy. (4) CBD-SnS/ECD-InSxOy. The valence band offsets ΔEV of those four heterojunctions are determined to be 1.34, 1.59, 0.77, and 0.74±0.3 eV, respectively.

Defect reduction in electrochemically deposited CdS thin films by annealing in 02

Abstract Using the electrochemical deposition method, CdS thin films were deposited from acid solutions (pH = 2.5) containing CdS0 4 and Na 2 S 2 0 3 on indium-oxide coated glass substrates. These films were annealed in N 2 , air, or O 2 atmosphere at 200–500°C for 30 min. Photoluminescence spectra were measured at 77 K. For the films annealed in N 2 , the band edge emission became weaker and the luminescence due to defects shifted to longer wavelengths as the annealing temperature was raised above 300°C. However, for the films annealed in air or O 2 , the band edge emission was observed strongly irrespective of the annealing temperature and the luminescence due to defects was weak. Thus the O 2 annealing is useful for the defects reduction.