Jeoung Ju Lee

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(1 0 0) 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 0.46 V. 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.

The Burstein-Moss effect in Cu2GeSe3:Co2+ single crystals

Cu2GeSe3 and Cu2GeSe3:Co2+ single crystals are grown using the modified Bridgman method. The grown single crystals have orthorhombic structures. The energy band gaps for Cu2GeSe3 and Cu2GeSe3:Co2+ single crystals measured at 298 K were about 0.789 and 0.798 eV, respectively, and these gaps are due to direct transitions. The Burstein-Moss effect due to overlapping of the energy level of Co2+(Td) and the conduction band of the Cu2GeSe3:Co2+ is observed.

Growth of epitaxial C54 TiSi2 on Si(111) substrate by in situ annealing in ultrahigh vacuum

The growth of Ti and the formation of epitaxial Ti silicide on Si(111)‐7×7 were investigated by using reflection high‐energy electron diffraction (RHEED) and high‐resolution transmission electron microscopy (HRTEM). The growth mode of Ti is Stransky–Krastanov type when the substrate temperature is room temperature (RT). On the other hand, it is Volmer–Weber type when the substrate temperature is ∼550 °C. The HRTEM lattice image and transmission electron diffraction pattern show that C54 TiSi2 is grown epitaxially on a Si substrate when 160 ML of Ti is deposited on a Si(111)‐7×7 surface at RT followed by in situ annealing at 750 °C for 10 min in ultrahigh vacuum (UHV). The TiSi2/Si interface is somewhat incoherent, but the developed TiSi2 crystallites are single crystal with matching face relationships of TiSi2(111)∥Si(111), TiSi2(311)∥Si(111), and TiSi2(022)∥Si(111). A thin single‐crystal Si overlayer with [111] direction is grown on the TiSi2 surface when TiSi2/Si(111) is annealed at ∼900 °C in UHV, whic...

Clarification of Mn–Zn interaction for InMnP:Zn epilayer by photoluminescence and x-ray photoelectron spectroscopy

Transition related to the Mn–Zn interaction was observed in photoluminescence (PL) study of the InMnP:Zn epilayer and the peak position blueshifted with increasing Mn concentration. X-ray photoelectron spectroscopy was used to clarify the blueshift of the PL peak. The binding energy shifts of Mn 2p and Zn 2p core levels indicative of the interaction between Mn and Zn were observed. This mutual interaction between Mn 2p and Zn 2p agrees with the result that the Mn-related transition in InMnP:Zn codoped with Zn is shifted to the higher energy region in comparison with InMnP without additional doping of Zn.

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.

Optical properties of undoped and Co2+-doped Cd2GeSe4 single crystals

Cd2GeSe4 and Cd2GeSe4:Co2+ (Co: 0.2, 0.3, 0.4, and 0.5 mol %) single crystals with a rhombohedral (hexagonal) structure were grown by the vertical Bridgman method. The structural and optical properties of Cd2GeSe4:Co2+ (Co: 0.2, 0.3, 0.4, and 0.5 mol %) were characterized by x-ray diffraction and optical absorption measurements at room temperature (298 K). The lattice constants, a0 and c0, increased when increasing Co2+ in the Cd2GeSe4:Co2+ crystal to 0.3 mol %. They increased sharply when increasing Co2+ to 0.4 and 0.5 mol %. The optical energy band gap of the Cd2GeSe4:Co2+ crystal decreased when increasing Co2+ in the Cd2GeSe4:Co2+ crystal to 0.3 mol % and it also decreased sharply when increasing the amount of Co2+ to 0.4 and 0.5 mol %. Two impurity optical absorption bands were observed at wavelength ranges of 1300–1900 nm and 700–900 nm. These bands originated from the Co2+ ions located at the C3v symmetry point in the Cd2GeSe4:Co2+ crystal.

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.

Characteristics of Simultaneous Studies of Both Undoped and p-type GaN Implanted with Mn+ (5 and 10 at.%)

GaMnN and GaMnN:Mg layers were prepared using implantation of 5 and 10 at.% Mn ions into undoped GaN and p-type GaN:Mg, respectively. Both samples revealed that two precipitate phases, Ga5:2Mn and Mn3Ga, coexist with the crystalline phase GaMnN. The ferromagnetic transition showed two kinds of behaviors; i.e., a rapid transition from GaMnN at lower temperatures (75 100 K) and a released transition from Ga5:2Mn and Mn3Ga at higher temperatures (above 300 K). The TC of GaMnN for Mg-codoped GaMnN ( 100 K) was observed to be higher than that for undoped GaMnN ( 75 K).

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.

Optical absorption and photoluminescence characteristics of Cd2GeSe4 single crystals

Cd2GeSe4 single crystals were grown by using a modified Bridgmann method. The optical energy band gap obtained from the optical absorption measurement was about 1.922±0.002 eV at 10 K and 1.707±0.002 eV at 298 K. In the photoluminescence (PL) spectra measured at temperatures below 70 K, two peaks were distinguished. One corresponds to the ground state (n=1) and the other corresponds to the excited state (n=2) of free exciton. The binding energy of the exciton was about 5.2 meV. The energy band gap obtained from the PL measurements was 1.9236 eV at 10 K.