Hyeon Soo Kim

A study of conduction of ZnO film/p-Si heterojunction fabricated by photoinduced electrodeposition under illumination

Thin ZnO films were directly grown on p-Si(1u20090u20090) substrates by photoinduced electrodeposition under illumination. In this case, p-Si wafer behaves as a photocathode. At the initial deposition stage, it has been found that the ZnO films grew through three-dimensional instantaneous nucleation followed by diffusion-limited growth mode. In this study, we report that the conductivity type of ZnO films can be changed from n-type to p-type by varying the relative concentration of oxygen in ZnO films through the thermal treatment in air ambient without any doping process. The electrical properties of ZnO/p-Si heterojunctions were investigated via current–voltage (I–V) characteristics. These heterojunctions showed good diode-like, rectifying I–V characteristics and the turn-on voltages of the n-ZnO/p-Si and p-ZnO/p-Si heterojunctions were found to be 0.56 and 0.46u2009V. From the analysis of temperature dependence of the I–V characteristics, these heterojunctions exhibited that the charge carriers are mainly transported by the activation of the carriers across the barrier height but in a low voltage region under forward bias, transported through the multi-step tunnelling-assisted carrier capture-emission mechanism.

Current Density and Thickness Effects on Magnetic Properties of Electrodeposited CoPt Magnetic Films

The dominant magnetization reversal behavior of electrodeposited CoPt samples with various thicknesses deposited at different current densities was the domain wall motion by means of wall pinning. The magnetic interaction mechanism was dipolar interaction for all samples. The dipolar interaction strength was significantly affected by the sample thickness rather than by the current density, while the magnetic properties were closely related to the current density.

Growth Kinetics of Fe Films Electrodeposited on n-Si(111)

Iron thin films were grown directly on n-Si(111) substrates by pulsed electrodeposition in a non-aqueous 0.1 M FeCl2 electrolyte solution. In this solution, Fe2+/Si interface showed a good diode behavior by forming a Schottky barrier. From single-step potential experiment in the potential ranges from 1.0 to 1.4 V, the formation of Fe nuclei in the early deposition stages was proceeded according to the three dimensional (3D) instantaneous nucleation followed by diffusion-limited growth rather than a progressive one. When depositing Fe using pulse potentials with the maximum voltage of 1.0 and 1.5 V, it was found that nucleation mechanism of Fe is similar with the results for the case of single-step potential experiment. However, nucleation during depositing Fe at 2.0 V initiated according to the progressive mechanism. Fe thin films, which obtains from pulse potential of 1.4 V with a frequency of 300 Hz, revealed a highly oriented columnar structures perpendicular to the surface of Si(111) and that only the single phase α-Fe(110) was grown on Si(111) substrate.

Epitaxial Growth of GaN on LaAlO3(100) Substrate by RF Plasma Assisted Molecular Beam Epitaxy.

About 0.4-µm-thick GaN films were epitaxially grown on a LaAlO3(100) substrate by rf plasma assisted molecular beam epitaxy. The growth mode was monitored by reflection high-energy electron diffraction and the crystalline quality of the GaN films was characterized by X-ray diffraction and transmission electron microscopy. The matching face relationship between GaN and the LaAlO3(100) substrate was [0001]GaN ∥[100]LaAlO3 and [0110]GaN ∥[011]LaAlO3, and a lattice mismatch of ~3% for the [011] plane was estimated.

Magnetic Interaction Effect on Activation Volume and Area of CoPt Magnetic Films

The magnetic interaction effect on the magnetic activation volume and area of electrodeposited CoPt magnetic films was investigated. The dipolar interaction was predominant interaction mechanism for all samples. And the interaction strength was increased with decreasing current density and increased with increasing sample thickness. Although the activation volumes of the samples fabricated at low current density were larger than those of the high current density samples, the sample thickness seemed to have little influence on the variation of activation volume. But it was found that the activation area was apparently affected by the magnetic interaction strength as well as the current density.

Magnetic Interaction and Switching Volumes in CoSm/Cr Magnetic Films

The sputtering pressure dependence of magnetic switching volume and the nature of magnetic intergranular interaction in CoSm/Cr films have been investigated using several magnetic characterization techniques. As the results, we found that magnetic switching volume strongly correlates to the nature and strength of magnetic intergranular interaction determined on the basis of dc demagnetization remanence and isothermal remanence curves. Also the sign of interaction field factor is closely related to the nature of magnetic intergranular interaction.

Defect Reduction in AlxGa1-xN Films Grown by Metal Organic Chemical Vapor Deposition

The grain size of AlxGa1-xN films grown on c-plane sapphire substrates was been measured using the X-ray diffraction (XRD) technique. The grain size increases with increasing Al content. It is evident that films with large grain sizes have less defect scattering, and hence, conductivity increases with the grain size. Apparently, the addition of Al to the epilayer increases conductivity.