Naozumi Fujiwara

Passivation of defects in polycrystalline Cu2O thin films by hydrogen or cyanide treatment

The effects of the passivation of defects in polycrystalline nitrogen-doped cuprous oxide (Cu 2 O) thin films with hydrogen or cyanide treatment were studied. In the photoluminescence (PL) measurements, although the emission was not observed before treatment, luminescence of Cu 2 O at around 680 nm was observed after each treatment. This improvement in the luminescence property may be due to the passivation of non-radiative recombination centers by H or CN. The hole carrier concentration increased from the order of 10 16 to 10 17 cm -3 with hydrogen or cyanide treatment. From these results, both the hydrogen and cyanide treatments were found to be very effective to passivate defects and improve the optical and electrical properties of polycrystalline Cu 2 O thin films. The thermal stability of the passivation effects by the cyanide treatment is, however, superior to that by the hydrogen treatment.

Passivation of defects in nitrogen-doped polycrystalline Cu2O thin films by crown-ether cyanide treatment

Crown-ether cyanide treatment, which simply involves immersion in KCN solutions containing 18-crown-6 followed by rinse, is studied in relation to electrical and optical properties of nitrogen-doped, polycrystalline Cu2O thin films, and its effect is compared with that of hydrogen treatment. By the crown-ether cyanide treatment, the luminescence intensity due to the near-band-edge emission of Cu2O at around 680 nm is enhanced, and the hole density is increased from the order of 1016 to 1017 cm−3, analogous to hydrogen treatment. The effects of the passivation by the hydrogen treatment completely disappear after annealing at 350 °C, while those of the crown-ether cyanide treatment stay unchanged after the same annealing treatment. From these results, the crown-ether cyanide treatment for polycrystalline Cu2O thin films can be concluded to be a more suitable method of passivating defects than the hydrogen treatment.

Mechanism of Copper Removal from SiO2 Surfaces by Hydrogen Cyanide Aqueous Solutions

Hydrogen cyanide (HCN) aqueous solutions can remove copper (Cu) contaminants from SiO 2 surfaces completely even when the cleaning is performed using dilute (e.g., 0.027 wt %) HCN aqueous solutions at 25°C. When pH of the HCN solutions is set at 10, Cu contaminants with a concentration of ∼2 X 10 12 atoms/cm 2 can be removed below ∼3 × 10 9 atoms/cm 2 taking only 10 s. The concentrations of Cu + and [Cu(CN) 2 ] - ions in the HCN solutions drastically decrease with pH, while those of [Cu(CN) 3 ] 2- and [Cu(CN) 4 ] 3- ions increase. The dissociation probability of HCN exponentially increases with pH.Therefore, the improvement of the cleaning ability with pH is attributable to (i) an increase in the concentration of CN - ions, and (ii) the prevention of readsorption due to the formation of stable Cu-cyano complex ions. Measurements of surface Cu concentrations on the SiO 2 surfaces contaminated by the immersion in the CuCl 2 -containing HCN solutions clarify the mechanism of Cu removal. The rate-determining step is a reaction between SiO-CuCN on the surface and CN - ions in the solution to form [Cu(CN) 2 ] - complex ions. The equilibrium constant of this reaction is found to be 4.1 x 10 5 M. This large value shows that desorption of [Cu(CN) 2 ] - proceeds much more easily than adsorption.

Investigation of electrical, structural, and optical properties of very thin oxide/a-Si:H/c-Si interfaces passivated by cyanide treatment

The paper deals with investigation of electrical, structural and optical properties of very thin oxide/a-Si:H interfaces passivated by chemical treatment by KCN and HCN solutions. The oxide layers were prepared by thermal, chemical and plasma or ion beam assisted oxidations. Interface properties were evaluated by charge version of deep level transient spectroscopy, C-V measurements, X-ray diffraction (in both Bragg-Brentano and grazing incidence modes), optical reflectance (based on genetic algorithm) and photoluminescence. Considerable interest was devoted to distribution of three dominant groups of a-Si:H defect states in the band gap of the semiconductor as well as their response to bias annealing and light soaking experiments. We will present also dominant result - increase of the efficiency of a-Si:H based solar cells after chemical treatment. Finally, we will present the chemical passivation and oxidization as promising techniques suitable for applications in the field of nanotechnology.