Kyung-Mun Kang

The CO gas sensing properties of direct-patternable SnO2 films containing graphene or Ag nanoparticles

The gas sensing properties of direct-patternable SnO2 thin films prepared by photochemical solution deposition were improved by an incorporation of graphene or Ag nanoparticles. The CO gas sensitivity of the SnO2 thin film was 3.65, but increased to 6.84 and 18.06 by the incorporation of graphene and Ag nanoparticles, respectively. Direct-patterning of graphene or Ag nanoparticles incorporated SnO2 thin films can be performed at the 40 μm scale pattern without a photoresist or an etching process.

Non-laminated growth of chlorine-doped zinc oxide films by atomic layer deposition at low temperatures

Chlorine doping in a ZnO matrix to a concentration of 0.65 ± 0.05 at% was accomplished via atomic layer deposition using a home-made chlorine source at a low deposition temperature of 140 °C. Structural and morphological properties were investigated using X-ray diffraction, field emission scanning electron microscopy, and grazing incidence wide-angle X-ray diffraction. The introduction of chlorine into the ZnO matrix resulted in significant grain growth reorientation due to chlorine doping in the oxygen sites of ZnO. Cl− ions preferentially occupied the substitutional O− ion site and O vacancies, and the preferential growth in the {100} planes changed to growth in the {002} planes along the longitudinal direction of the hexagonal wurtzite structure as a function of the Cl doping levels. This important phenomenon was explained by a passivation effect, resulting from the chlorine doping mechanism; this was elucidated using transmission electron microscopy. The optical transmittances of the undoped ZnO and ZnO:Cl films were approximately the same (88%), but the optical band gap was increased by the introduction of a Cl dopant in ZnO due to the Burstein–Moss effect. The lowest resistivity of ZnO:Cl was 1.215 × 10−2 Ω cm, and the corresponding carrier concentration and mobility were 5.715 × 1019 cm−3 and 31.81 cm2 V−1 s−1, respectively. Finally, the calculated doping efficiency of chlorine in ZnO was 10.8%, which was higher than that of aluminum-doped ZnO, even though the deposition temperature was very low when applied to plastic substrates due to the non-laminated growth of ZnO:Cl films.

Enhanced hole injection into indium-free organic red light-emitting diodes by fluorine-doping-induced texturing of a zinc oxide surface

We investigated the effect of fluorine (F)-doping-induced texturing of a zinc oxide (ZnO) surface to enhance the hole injection properties of an organic light emitting diode (OLED) device. In this work, 250 nm thick ZnO anodes doped with 0, 0.2, 0.5, and 0.7 at.% F were grown on liquid crystal display (LCD) glass substrates by atomic layer deposition (ALD) at a low temperature (140 °C). The sheet resistance of undoped ZnO and F-doped ZnO (ZnO:F) anodes decreased with increased F-doping in the ZnO matrix. Conversely, the work functions of the doped ZnO anodes gradually increased with the increase in surface texturing caused by an increase in the amount of exposed (100) planes. Finally, the best OLED performance was obtained for a ZnO anode containing 0.5 at.% F; the work function value of this film was 4.74 eV. The highest luminance and current density values (at a bias of 20 V) were optimized to be 13 509.55 cd m−2 and 247.98 mA cm−2, respectively. These superior properties were obtained in an OLED device composed of a DNTPD/TAPC/Bebq2:10%-doped RP-411/Bphen/LiF/Al structure on a ZnO:F anode containing 0.5 at.% F.

Oxygen vacancy-passivated ZnO thin film formed by atomic layer deposition using H2O2

Intrinsic defect oxygen vacancies, which can easily form in ZnO films and result in a compensation effect on p-type dopants, have long prevented the preparation of high-quality p-type ZnO; consequently, the application of ZnO in optoelectronic devices has been adversely affected. Therefore, in this investigation, the passivation of oxygen vacancies in undoped ZnO using H2O2 as an oxygen source is studied using atomic layer deposition (ALD). The ALD growth window ranged from 60 to 150 °C, and the use of H2O2 as an oxygen source, instead of H2O, changed the preferred growth orientation from coexisting a- and c-axes to only the c-axis, which indicated that H2O2 can provide an oxygen-rich environment for the growth of ZnO. Photoluminescence results indicated that oxygen vacancies in the ZnO film reduced significantly when H2O2 was used as the oxygen precursor instead of H2O for film preparation. Further, oxygen vacancies can be suppressed more efficiently using H2O2 when ZnO films were deposited at lower temp...