Byung Du Ahn

Structural, electrical, and optical properties of p-type ZnO thin films with Ag dopant

p-type ZnO films have been fabricated on a (0001) Al2O3 substrate, using Ag2O as a silver dopant by pulsed laser deposition. The structural property of those films is systematically characterized by observing the shift of (0002) peak to investigate the substitution of Ag+ for Zn+. Narrow deposition temperature for Ag-doped p-type ZnO films has been obtained in the range of 200–250°C with the hole concentration of 4.9×1016–6.0×1017cm−3. A neutral acceptor bound exciton has been clearly observed by photoluminescence emitted at 3.317eV in Ag-doped p-type ZnO thin films.

Comparison of the effects of Ar and H2 plasmas on the performance of homojunctioned amorphous indium gallium zinc oxide thin film transistors

We proposed a homojunctioned amorphous InGaZnO (a-IGZO) thin film transistor (TFT) and compared its performance to that of a conventional structured TFT. The source/drain regions were formed in the a-IGZO channel layer using Ar and H2 plasma treatments, respectively. Hydrogen itself was found to act as a carrier of donors with H2 plasma treatment, which had effects to a depth of 50 nm. Our TFT had a field-effect mobility of 7.27 cm2/V s, an on/off ratio of 1.2×107, a threshold voltage of 0.96 V, and a subthreshold swing of 0.49 V/decade.

Effect of indium composition ratio on solution-processed nanocrystalline InGaZnO thin film transistors

The effects of the indium content on characteristics of nanocrystalline InGaZnO (IGZO) films grown by a sol-gel method and their thin film transistors (TFTs) have been investigated. Excess indium incorporation into IGZO enhances the field effect mobilities of the TFTs due to the increase in conducting path ways and decreases the grain size and the surface roughness of the films because more InO2− ions induce cubic stacking faults with IGZO. These structural variations result in a decrease in density of interfacial trap sites at the semiconductor-gate insulator interface, leading to an improvement of the subthreshold gate swing of the TFTs.

Investigation of the effects of Mg incorporation into InZnO for high-performance and high-stability solution-processed thin film transistors

We have fabricated high-performance and high-stability sol-gel-processed MgInZnO thin films transistors with varying Mg content. As the Mg content was increased, the turn-on-voltage increased and the off-current decreased. This is because the incorporation of Mg (with low standard electrode potential and high optical band gap, Eopt, when oxidized) causes reduction in the oxygen vacancy, acting as a carrier source, and an increase in Eopt of the film. This results in reduction in carrier concentration of the film. Small grains and smooth morphology by varying the Mg content lead to an improvement of the mobility, on-current, and subthreshold gate swing.

Investigating addition effect of hafnium in InZnO thin film transistors using a solution process

The effects of adding Hf into a InZnO (IZO) system, particularly the electrical characteristics of their thin film and thin film transistors (TFTs), were investigated as a function of atomic concentration from 0 to 10 at. % of Hf and Ga/Zn. Because Hf has a high affinity for oxygen in IZO system, the Hf suppresses carrier generation more effectively than does Ga. At 10 at. % of Hf/Zn atomic concentration, the HfInZnO TFTs showed wider on-to-off ratios than those of GaInZnO TFTs due to the low standard-electrode-potential of Hf and sharp subthreshold swings due to low trap density.

Investigation on the p-type formation mechanism of arsenic doped p-type ZnO thin film

The photoluminescence spectra of As doped p-type ZnO thin films reveal neutral acceptor bound exciton of 3.3437eV and a transition between free electrons and acceptor levels of 3.2924eV. Calculated acceptor binding energy is about 0.1455eV. Thermal activation and doping mechanism of this film have been suggested by the analysis of x-ray photoelectron spectroscopy. p-type formation mechanism of As doped ZnO thin film is related to the AsZn–2VZn complex model. ZnO-based p-n junction was fabricated by the deposition of an undoped n-type ZnO layer on an As doped p-type ZnO layer.

Synthesis and analysis of Ag-doped ZnO

The solid-solid interaction and thermal decomposition behavior of 2wt% Ag2O in ZnO powder have been investigated by using thermogravimetry analysis and differential thermal analysis. Ag2O, which remained stable in ZnO up to 200°C, was observed to be thermally decomposed to Ag+ ions in the temperature range of 200–250°C, suggesting that Ag+ ions were diffused into ZnO matrix. Based on thermal analysis, ZnO:Ag films have been fabricated on a (001) Al2O3 substrate using specifically synthesized Ag-doped ZnO target by pulsed laser deposition. The effect of (002) peak shift on the structural property of Ag-doped ZnO films has been systematically characterized to investigate the influence of the substitution of Ag+ for Zn+. Ag-doped p-type ZnO films have been successfully grown at a deposition temperature in the range of 200–250°C, which is in good agreement with thermally decomposed temperature for Ag2O to Ag+ in ZnO powder, with hole concentrations of 4.9×1016–6.0×1017cm−3, hole mobilities of 0.29–2.32cm2∕Vs,...

Investigation on doping dependency of solution-processed Ga-doped ZnO thin film transistor

Ga-doped ZnO (GZO) thin film transistors (TFTs) were fabricated based on the solution-processed method and GZO TFTs were investigated according to the variation of the Ga doping concentration [Ga∕Zn (%)]. A field-effect mobility of 1.63cm2∕Vs and a drain current on/off ratio of 4.17×106 were observed in the 5.4 % Ga-doped TFT. This result shows good agreement with its structural properties and electrical properties of the GZO channel layer. It is believed that the optimal and desirable electrical properties of the TFTs can be obtained by adjusting the Ga doping concentration.

Organic photovoltaic devices with Ga-doped ZnO electrode

The authors report two organic photovoltaic devices using a Ga-doped ZnO (GZO) film as a transparent conducting electrode. In the first structure, the conventional In2O3:Sn hole-collecting anode was replaced by GZO and an efficiency of 0.35% was obtained. The second has the inverse structure where GZO was used as the electron-collecting cathode and gave a nonoptimized device efficiency of about 1.4%. Furthermore, this inverse structure of GZO devices provides a passivation layer to protect the active layer from the atmosphere.

Effect of rapid thermal annealing on electrical and optical properties of Ga doped ZnO thin films prepared at room temperature

Ga doped ZnO (GZO) thin films were prepared by pulsed laser deposition on glass substrate at room temperature. Structural, optical, and electrical properties of these films were analyzed in order to investigate their dependence on oxygen pressure and rapid thermal annealing (RTA) temperature. High quality GZO films with a low resistivity of 2.92×10−4Ωcm and a transparency above 94% were able to be formed at an oxygen pressure of 3×10−2Torr and a RTA temperature of 400°C. A four point probe method, x-ray diffraction, atomic force microscopy, and ultraviolet–near-infrared grating spectrometer are used to investigate the properties of GZO films.