Jong Ha Moon

Heteroepitaxial growth behavior of Mn-doped ZnO thin films on Al2O3 (0001) by pulsed laser deposition

Heteroepitaxial growth behavior of Mn-doped ZnO thin films (Zn1−xMnxO) on Al2O3 (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content (0.00⩽x⩽0.35) using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a 30° rotation of ZnO basal planes with respect to the Al2O3 substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping (x=0.05) not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagneti...

Effect of film thickness on the structural and electrical properties of Ga-doped ZnO thin films prepared on glass and Al 2 O 3 (0001) substrates by RF magnetron sputtering method

Thin films of Ga-doped ZnO (GZO) were prepared on glass and Al 2 O 3 (0001) substrates by using RF magnetron sputtering at a substrate temperature of 350 °C, RF power of 175 W, and working pressure of 6 mTorr. The effect of film thickness and substrate type on the structural and electrical properties of the thin films was investigated. X-ray diffraction study showed that GZO thin films on glass substrates were grown as a polycrystalline hexagonal wurtzite phase with a c-axis preferred, out-of-plane orientation and random in-plane orientation. However, GZO thin films on Al 2 O 3 (0001) substrates were epitaxially grown with an orientation relationship of . The structural images from scanning electron microscopy and atomic force microscopy showed that the GZO thin films on glass substrates had a rougher surface morphology than those on Al 2 O 3 (0001) substrates. The electrical resistivity of 1000 nm-thick GZO thin films grown on glass and Al 2 O 3 (0001) substrates was 3.04 × 10 −4 Ωcm and 1.50 × 10 −4 Ωcm, respectively. It was also found that the electrical resistivity difference between the films on the two substrates decreased from 9.48 × 10 −4 Ωcm to 1.45 × 10 −4 Ωcm with increasing the film thickness from 100 nm to 1000 nm.

Effects of Pt/Pd Co-doping on the sensitivity of SnO2 thin film sensors

SnO2 thin films were deposited on thermally oxidized Si substrates by RF magnetron sputtering. The sensing properties of pure, Pt-doped, Pd-doped, and Pt/Pd co-doped SnO2 thin films were investigated for two gases, CO and CH4. Pd was added to the bulk of SnO2 thin film to induce the Fermi energy control effect while Pt was doped on the surface of SnO2 thin film for the spillover effect. When 50 A Pt was co-doped on the surface of SnO2 thin film with 0.5 wt% Pd added to the bulk, the maximum sensitivities were obtained for both the gases at 350°C due to the contribution of the two different mechanisms.

Effects of Cu/In compositional ratio on the characteristics of CuInS 2 absorber layers prepared by sulfurization of metallic precursors

This paper investigates the effects of the Cu/In compositional ratio on morphological, structural and optical properties of CuInS2 (CIS) absorber layers formed by sulfurization of In/Cu stacked precursors. In/Cu stacked precursors were prepared on Mo-coated soda-lime glass substrates by DC magnetron sputtering method. The Cu/In compositional ratio in the precursor thin film was varied from 0.55 to 1.44. The as-deposited stacked precursor thin films were sulfurized using a tubular furnace annealing system in a mixture of N2 (95%) + H2S (5%) atmosphere at 450°C for 1 hour. X-ray diffraction patterns and Raman spectra results showed that the sulfurized thin films contained both tetragonal CIS and a Cu-based secondary phase, except for the film with a Cu/In compositional ratio of 0.55. Field emission-scanning electron microscopy study showed that the microstructure of the sulfurized CIS thin films became denser with increasing Cu/In compositional ratio. Optical properties of the CIS thin films showed that all the CIS thin films had a good absorption coefficient over 104 cm−1 in the visible region. The direct band gap energy of the sulfurized CIS thin films decreased from 1.39 eV to 1.08 eV with increasing Cu/In compositional ratio. These results demonstrated the effect of the Cu/In compositional ratio on the properties of the CIS thin films and the consequent importance of precisely controlling the metal ratio in the precursor film in order to control the properties of absorber layers in thin film solar cells.

Evolution of detrimental secondary phases in unstable Cu2ZnSnS4 films during annealing

The formation and phase evolution of Cu-S based compounds in kesterite Cu2ZnSnS4 (CZTS) absorbing thin films is a critical factor affecting the performance of these materials in thin film solar cells (TFSCs). However, to the best of our knowledge, few studies have investigated the segregation of Cu-S based compounds in kesterite thin films during the sulfurization process. In this study, stacked Cu/SnS2/ZnS precursor thin films were annealed to systematically study the segregation and phase evolution of Cu-S based compounds in kesterite thin films subjected to functional sulfurization times at 550°C. The stacked precursor thin films appeared to be fully transformed to the pure kesterite phase when the sulfurization times are over 30 min. when analyzed using X-ray diffraction and Raman spectroscopy. However, transmission electron microscopy (TEM) characterization revealed that Cu-S based compounds segregated in the kesterite CZTS thin films annealed for 120 min. at 550°C. Based on the experimental results obtained for functional sulfurization times, a mechanism for Cu-S based compounds segregation and the phase evolution process is proposed.

Electronic structure of P-doped ZnO films with p-type conductivity

The electronic structure of laser-deposited P-doped ZnO films was investigated by X-ray absorption near-edge structure spectroscopy (XANES) at the O K-, Zn K-, and Zn L3-edges. While the O K-edge XANES spectrum of the n-type P-doped ZnO demonstrates that the density of unoccupied states, primarily O 2p-P 3sp hybridized states, is significantly high, the O K-edge XANES spectrum of the p-type P-doped ZnO shows a sharp decrease in intensity of the corresponding feature indicating that P replaces O sites in the ZnO lattice, and thereby generating P(O). This produces holes to maintain charge neutrality that are responsible for the p-type behavior of P-doped ZnO. Both the Zn K-, and Zn L3-edge XANES spectra of the P-doped ZnO reveal that Zn plays no significant role in the p-type behavior of ZnO:P.

Studies on the Controlling of the Microstructural and Morphological Properties of Al Doped ZnO Thin Films Prepared by Hydrothermal Method

Al doped ZnO (AZO) thin films were prepared on ZnO coated glass substrates by hydrothermal synthesis technique using aqueous solutions containing zinc nitrate hexahydrate, ammonium hydroxide, and different sodium citrate concentrations at 60 °C for 6 h. The effects of different trisodium citrate concentrations on the microstructural, crystallinity, morphological, optical, and chemical properties of thin films were investigated. X-ray diffraction studies showed that the AZO thin films were grown as a polycrystalline wurtzite hexagonal phase with a c-axis preferred orientation and without an unwanted second phase regardless of trisodium citrate concentrations. The thickness and grain sizes of AZO thin films decreased with increasing trisodium citrate concentration. The microstructure of AZO thin films was changed from flat to needle shaped and the morphology was smoother with increasing trisodium citrate concentrations. The AZO thin films have a high transmittance in the visible region ranging from 75 to 85% and a sharp edge from 366 to 374 nm.

Synthesis of ZnO nanowalls on Al2O3 (0001) by catalyst-free metalorganic chemical vapor deposition

We report the synthesis of epitaxially aligned ZnO nanowalls on Al2O3 (0001) by metalorganic chemical vapor deposition without using any metal catalyst. ZnO nanowalls of 60–150 nm thickness are uniformly assembled on the substrate. A small amount of ZnO nanowires additionally grow and are coupled with the ZnO nanowalls. Interestingly, the crystals in the ZnO nanowalls are aligned in both the out-of-and in-plane direction. A strong UV emission at around 380 nm, observed in a room temperature photoluminescence spectrum, indicates excellent optical quality of the ZnO nanowalls.

Effect of Sputtering Powers on Mg and Ga Co-Doped ZnO Thin Films with Transparent Conducting Characteristics

ZnO thin films co-doped with Mg and Ga (MxGyZzO, x + y + z = 1, x = 0.05, y = 0.02 and z = 0.93) were prepared on glass substrates by RF magnetron sputtering with different sputtering powers ranging from 100 W to 200 W at a substrate temperature of 350 oC. The effects of the sputtering power on the structural, morphological, electrical, and optical properties of MGZO thin films were investigated. The X-ray diffraction patterns showed that all the MGZO thin films were grown as a hexagonal wurtzite phase with the preferred orientation on the c-axis without secondary phases such as MgO, Ga2O3, or ZnGa2O4. The intensity of the diffraction peak from the (0002) plane of the MGZO thin films was enhanced as the sputtering power increased. The (0002) peak positions of the MGZO thin films was shifted toward, a high diffraction angle as the sputtering power increased. Cross-sectional field emission scanning electron microscopy images of the MGZO thin films showed that all of these films had a columnar structure and their thickness increased with an increase in the sputtering power. MGZO thin film deposited at the sputtering power of 200 W showed the best electrical characteristics in terms of the carrier concentration (4.71 × 1020 cm−3), charge carrier mobility (10.2 cm2 V−1 s−1) and a minimum resistivity (1.3 × 10−3Ωcm). A UVvisible spectroscopy assessment showed that the MGZO thin films had high transmittance of more than 80 % in the visible region and that the absorption edges of MGZO thin films were very sharp and shifted toward the higher wavelength side, from 270 nm to 340 nm, with an increase in the sputtering power. The band-gap energy of MGZO thin films was widened from 3.74 eV to 3.92 eV with the change in the sputtering power.

Recrystallization of ion-beam amorphized Bi2Sr2Ca1Cu2Ox thin films on SrTiO3(001)

Abstract Effects of oxygen ion irradiation followed by thermal annealing of single phase (00 l ) oriented Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi-2212) films on SrTiO 3 (001) synthesized by pulsed laser deposition were studied. Differently from as-deposited films, ion irradiated and thermally annealed ones show a leaf-like grain morphology and a significantly improved electric resistivity behavior. The results suggest that the process, that is, amorphization by ion irradiation followed by recrystallization by thermal annealing, may be a new method to enhance superconducting properties of Bi-2212 films.