Kwun-Bum Chung

Studies on optical, structural and electrical properties of atomic layer deposited Al-doped ZnO thin films with various Al concentrations and deposition temperatures

We investigated transparent conducting aluminium-doped zinc oxide thin films fabricated by atomic layer deposition (ALD). For the thermal ALD, diethylzinc and trimethylaluminium were used as the Zn and Al precursors, respectively. The electrical, structural and optical properties were systematically investigated as functions of the Al doping contents and deposition temperature. The best resistivity and transmittance (4.2 mΩ cm and ~85%) were observed at an Al doping concentration of about 2.5 at% at 250 °C. An increase in the carrier concentration was observed with increasing deposition temperature and doping concentration. This can be explained by the effective field model of layered structures. Also, the enhancement of the mobility with increasing doping concentration was studied by the grain-boundary scattering and percolative conduction mechanism. By correlating the electrical and structural properties, it was found that varying the carrier concentration was more effective in changing the mobility than the grain-boundary scattering, due to the hopping conduction.

The impact of SiNx gate insulators on amorphous indium-gallium-zinc oxide thin film transistors under bias-temperature-illumination stress

The threshold voltage instability (Vth) in indium-gallium-zinc oxide thin film transistor was investigated with disparate SiNx gate insulators under bias-temperature-illumination stress. As SiNx film stress became more tensile, the negative shift in Vth decreased significantly from −14.34 to −6.37 V. The compressive films exhibit a nitrogen-rich phase, higher hydrogen contents, and higher N–H bonds than tensile films. This suggests that the higher N–H related traps may play a dominant role in the degradation of the devices, which may provide and/or generate charge trapping sites in interfaces and/or SiNx insulators. It is anticipated that the appropriate optimization of gate insulator properties will help to improve device reliability.

Composition, structure, and electrical characteristics of HfO2 gate dielectrics grown using the remote- and direct-plasma atomic layer deposition methods

Hafnium oxide thin films were deposited using both the remote-plasma atomic layer deposition (RPALD) and direct-plasma atomic layer deposition (DPALD) methods. Metal-oxide semiconductor (MOS) capacitors and transistors were fabricated with HfO2 gate dielectric to examine their electrical characteristics. The as-deposited RPALD HfO2 layer exhibited an amorphous structure, while the DPALD HfO2 layer exhibited a polycrystalline structure. Medium-energy ion scattering measurement data indicate that the interfacial layer consisted of interfacial SiO2−x and silicate layers. This suggests that the change in stoichiometry with depth could be related to the energetic plasma beam used in the plasma ALD process, resulting in damage to the Si surface and an interaction between Hf and SiO2−x. The as-deposited RPALD HfO2 films had better interfacial layer characteristics, such as an effective fixed oxide charge density (Qf,eff) and interfacial roughness than the DPALD HfO2 films did. A MOS capacitor fabricated using th...

Transparent and flexible amorphous In-Si-O films for flexible organic solar cells

We report on transparent amorphous In-Si-O (ISO) electrodes for flexible organic solar cells (FOSCs). Effective Si doping into the In2O3 matrix led to a completely amorphous ISO film as well as a low sheet resistance of 51.91 Ω/sq and a high near-infrared optical transmittance of 81.51% (550 nm), and which are desirable electrode characteristics for FOSCs. In addition, the ISO film showed outstanding flexibility in outer and inner bending tests due to the stable amorphous structure. Based on x-ray absorption spectroscopy and high resolution transmission microscope examinations, detailed microstructure and electronic structure of amorphous ISO film were investigated. Furthermore, FOSCs with an amorphous ISO anode showed an open circuit voltage (0.578 V), short circuit current (7.641 mA/cm2), fill factor (62.96%), and power conversion efficiency (2.78%), indicating that ISO is a promising flexible amorphous transparent electrode for FOSCs.

Mn-implanted dilute magnetic semiconductor InP:Mn

Unintentionally doped bulk InP was prepared by the liquid encapsulated Czochralski method and subsequently implanted with various doses of Mn+. The properties of Mn+-implanted InP:Mn were investigated by various measurements. The results of energy dispersive x-ray peaks displayed injected concentrations of Mn of 0.8% and 8.8%, respectively. The results of photoluminescence (PL) measurement showed that optical broad transitions related to Mn appeared near 1.089, 1.144, and 1.185 eV in samples with various doses of Mn+. It was confirmed that the photoluminescence peaks near 1.089, 1.144, and 1.185 eV were Mn-correlated PL bands by the implantation of Mn. Ferromagnetic hysteresis loops measured at 10 K were observed and the temperature-dependent magnetization showed ferromagnetic behavior around 90 K, which almost agreed with the theoretical prediction (Tc∼70 K).

Device performance and bias instability of Ta doped InZnO thin film transistor as a function of process pressure

The device performance and bias instability of radio frequency (RF) sputtered Ta doped InZnO thin film transistors (TFTs) were investigated as a function of deposition process pressure. Under low process pressure, the electrical characteristics of TaInZnO TFTs were enhanced with amorphous physical structure and the decrease of oxygen deficient bonding states. These changes were correlated with the evolution of electronic structure, such as band alignment and band edge states below the conduction band. As the process pressure decreased, the energy difference between conduction band minimum and Fermi level and the band edge states was decreased. In particular, the relative energy level of band edge states was moved into the deep level within bandgap, with the increase of process pressure.

Ferromagnetic behavior of p-type GaN epilayer implanted with Fe+ ions

p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe+ ions. The properties of Fe+ implanted GaN epilayers were investigated by various measurements. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 eV and around 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak around 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting above 350 K.

Structural Evolution and the Control of Defects in Atomic Layer Deposited HfO2–Al2O3 Stacked Films on GaAs

The structural characteristics and interfacial reactions of bilayered dielectric stacks of 3 nm HfO2/2 nm Al2O3 and 3 nm Al2O3/2 nm HfO2 on GaAs, prepared by atomic layer deposition (ALD), were examined during film growth and the postannealing process. During the postdeposition annealing (PDA) of the Al2O3/HfO2/GaAs structures at 700 °C, large amounts of Ga oxides were generated between the Al2O3 and HfO2 films as the result of interfacial reactions between interdiffused oxygen impurities and out-diffused atomic Ga. However, in the case of the HfO2/Al2O3/GaAs structures, the presence of an Al2O3 buffer layer effectively blocked the out-diffusion of atomic Ga, thus suppressing the formation of Ga oxide. Microstructural analyses showed that HfO2 films that were deposited on Al2O3/GaAs had completely crystallized during the PDA process, even at 700 °C, because of the Al2O3 diffusion barrier. Capacitance-voltage measurements showed a relatively large frequency dispersion of the Al2O3/HfO2/GaAs structure in accumulation capacitance compared to the HfO2/Al2O3/GaAs structure due to a higher interface state density. Conductance results revealed that the Al2O3 buffer layer on GaAs resulted in a significant reduction in gap states in GaAs. The induced gap state in the Al2O3/HfO2/GaAs structure originated from the out-diffusion of atomic Ga into the HfO2 film. Density functional theory calculations supported this conclusion.

Highly Conducting, Transparent, and Flexible Indium Oxide Thin Film Prepared by Atomic Layer Deposition Using a New Liquid Precursor Et2InN(SiMe3)2

Highly conductive indium oxide films, electrically more conductive than commercial sputtered indium tin oxide films films, were deposited using a new liquid precursor Et2InN(SiMe3)2 and H2O by atomic layer deposition (ALD) at 225-250 °C. Film resistivity can be as low as 2.3 × 10(-4)-5.16 × 10(-5) Ω·cm (when deposited at 225-250 °C). Optical transparency of >80% at wavelengths of 400-700 nm was obtained for all the deposited films. A self-limiting ALD growth mode was found 0.7 Å/cycle at 175-250 °C. X-ray photoelectron spectroscopy depth profile analysis showed pure indium oxide thin film without carbon or any other impurity. The physical and chemical properties were systematically analyzed by transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, optical spectrometer, and hall measurement; it was found that the enhanced electrical conductivity is attributed to the oxygen deficient InOx phases.

Activation of sputter-processed indium-gallium-zinc oxide films by simultaneous ultraviolet and thermal treatments.

Indium–gallium–zinc oxide (IGZO) films, deposited by sputtering at room temperature, still require activation to achieve satisfactory semiconductor characteristics. Thermal treatment is typically carried out at temperatures above 300 °C. Here, we propose activating sputter- processed IGZO films using simultaneous ultraviolet and thermal (SUT) treatments to decrease the required temperature and enhance their electrical characteristics and stability. SUT treatment effectively decreased the amount of carbon residues and the number of defect sites related to oxygen vacancies and increased the number of metal oxide (M–O) bonds through the decomposition-rearrangement of M–O bonds and oxygen radicals. Activation of IGZO TFTs using the SUT treatment reduced the processing temperature to 150 °C and improved various electrical performance metrics including mobility, on-off ratio, and threshold voltage shift (positive bias stress for 10,000 s) from 3.23 to 15.81 cm2/Vs, 3.96 × 107 to 1.03 × 108, and 11.2 to 7.2 V, respectively.