Hsin-Ying Lee

Metal–oxide–semiconductor devices using Ga2O3 dielectrics on n-type GaN

Using a photoelectrochemical method involving a He–Cd laser, Ga2O3 oxide layers were directly grown on n-type GaN. We demonstrated the performance of the resultant metal–oxide–semiconductor devices based on the grown Ga2O3 layer. An extremely low reverse leakage current of 200 pA was achieved when devices operated at −20u2009V. Furthermore, high forward and reverse breakdown electric fields of 2.80 MV/cm and 5.70 MV/cm, respectively, were obtained. Using a photoassisted current–voltage method, a low interface state density of 2.53×1011u2009cm−2u200aeV−1 was estimated. The varactor devices permit formation of inversion layers, so that they may be applied for the fabrication of metal–oxide–semiconductor field-effect transistors.

Optical properties of ZnO/GaN heterostructure and its near-ultraviolet light-emitting diode

We report on photoluminescence in a ZnO/GaN heterostructure, which showed a donor–acceptor pair emission band at 3.270 eV and the longitudinal optical phonon replicas at 12 K. In comparison with p-type GaN, the positions of the peaks are redshifted. This may be associated with the variation of the residual strain in the GaN layer of the heterostructure. Using this heterostructure, near-ultraviolet light-emitting diodes were fabricated and their electroluminescence properties were characterized.

Thermodynamic stability of Ga2O3(Gd2O3)∕GaAs interface

Ga2O3(Gd2O3)∕GaAs heterostructures have been annealed up to ∼780°C. Studies using x-ray reflectivity and high-resolution transmission electron microscopy have shown that the samples annealed under ultrahigh vacuum have maintained smooth and abrupt interfaces with the interfacial roughness being less than 0.2nm. The oxide remains amorphous, an important parameter for device consideration. Current–voltage and capacitance–voltage measurements have shown low leakage currents (10−8–10−9A∕cm2), a high dielectric constant of 15, and a low interfacial density of states (Dit) between gate dielectrics and GaAs. The attainment of a smooth interface between the gate dielectric and GaAs, even after high temperature annealing for activating implanted dopant, is a must to ensure the low (Dit) and to maintain a high carrier mobility in the channel of the metal–oxide–semiconductor field-effect transistor.

GaN MOS device using SiO 2 -Ga 2 O 3 insulator grown by photoelectrochemical oxidation method

We report on a SiO/sub 2/-Ga/sub 2/O/sub 3/ gate insulator stack directly grown on n-type GaN by the photoelectrochemical oxidation method. The resultant MOS devices are fabricated using standard photolithography and liftoff techniques. The effect of annealing temperature on the SiO/sub 2/-Ga/sub 2/O/sub 3//n-type GaN MOS devices is investigated. The properties of high breakdown field, low gate leakage current, and low interface state density are investigated for the MOS devices.

Effects of plasma treatment on the electrical and optical properties of indium tin oxide films fabricated by r.f. reactive sputtering

Abstract In this study, indium tin oxide (ITO) films were fabricated by r.f. reactive sputtering on glass substrates at room temperature. After the deposition process, the films were treated by oxygen and (30% H2+70% N2) gas mixture plasma, respectively. The effect of the plasma treatments on the electrical and optical properties of ITO films was then investigated. It was found that such parameters as the period and number of the plasma treatment had a great influence on the optoelectronic properties of the films. The property variation of the plasma treated films differed for the oxygen and the (30% H2+70% N2) gas mixtures. Some potential applications of plasma treated films are also discussed.

Structural and electrical characteristics of Ga2O3(Gd2O3)∕GaAs under high temperature annealing

Atomically smooth Ga2O3(Gd2O3)∕GaAs interface with low interfacial density of states and low electrical leakage currents have been achieved after the heterostructures were air exposed and tailor annealed to ∼750°C. The heat treatments, with annealing at an intermediate temperature of ∼300°C as a necessary step, were carried out under ultrahigh vacuum (UHV) and via standard rapid thermal annealing with flow of pure nitrogen gas. Furthermore, the oxide remains amorphous and minimal interfacial reaction occurred between the oxide and substrate, critical aspects for device performance. Studies using x-ray reflectivity and high-resolution transmission electron microscopy show that the interfacial roughness is <0.2 and <0.4nm for annealing under UHV and non-UHV, respectively. Electrical measurements on the metal-oxide-semiconductor diodes have exhibited low leakage currents (10−8–10−9A∕cm2), a dielectric constant of ⩾14, and a low interfacial density of states (Dit) of <1012cm−2eV−1.

Investigation of indium tin oxide/zinc oxide multilayer ohmic contacts to n-type GaN isotype conjunction

The ohmic performance of the ITO/ZnO multilayer deposited on n-type GaN layer was investigated. The best thermal annealing condition achieved for ohmic contact was 5 min at 500u200a°C, in hydrogen ambient. The measured specific contact resistance was 3×10−4 Ωu200acm2. Ohmic formation mechanisms would be attributed to the ITO/n-ZnO/n-GaN isotype conjunction and the reduction conduction band offset due to the quantum confinement effects in the thin ZnO layer.

Structure of HfO2 films epitaxially grown on GaAs(001)

High-quality HfO2 films of technologically important thickness ranging from 1.8to17nm have been grown epitaxially on GaAs (001) by molecular beam epitaxy. Thorough structural and morphological investigations were carried out by x-ray scattering and high-resolution transmission electron microscopy. The films exhibit an atomically sharp interface with the substrate and are of a monoclinic phase with predominant (001)-plane epitaxy between the HfO2 films and GaAs, in spite of a large lattice mismatch of >8.5%.

Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability

Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO2) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO2 nanocrystal sample prepared by a sol-gel method. Variations in local structures due to thermal annealing were observed and analyzed. Most importantly, our x-ray results provide direct experimental evidence for the existence of oxygen vacancies arising from local disorder and distortion of the oxygen sublattice in nanocrystalline ZrO2. These oxygen vacancies are regarded as the essential stabil...

Investigation of transparent and conductive undoped Zn2In2O5−x films deposited on n-type GaN layers

Transparent, conductive, multicomponent oxide films composed of undoped Zn2In2O5−x were deposited on n-type GaN layer using rf sputtering. We investigated the dependence of the surface, electrical, and optical properties on the sputtering parameters, including rf power, total pressure, and the post-deposition annealing process. We obtained high transparency (>80% in the visible and near-infrared ranges) and low electrical resistivity (2.58×10−4 Ωu200acm). Atomic force microscopy and optical transmittance measurements of Zn2In2O5−x films were used to investigate the mechanisms of resistivity variation in the films. The ohmic performances of Zn2In2O5−x contacts to the n-type GaN layer are also demonstrated.