Y.H. Kwon

GaN metal–oxide–semiconductor structures using Ga-oxide dielectrics formed by photoelectrochemical oxidation

GaN metal–oxide–semiconductor (MOS) capacitors were fabricated by using Ga oxide formed by photoelectrochemical oxidation of GaN. The electrical properties of the MOS structures as characterized by capacitance–voltage measurement were found to be dependent on the oxidation time and posttreatment. Positive flatband voltage was observed in devices with thin oxide layers indicating the existence of negative oxide charge. Very thin oxide exhibits high capacitance and reverse leakage, which can be reduced by rapid thermal annealing (RTA). Passivation of the interface by RTA is partially responsible for the improvement. Thicker oxide layers exhibit improved electrical properties. Low density of interface states (∼1011 eV−1 cm−2) was obtained in the Ga-oxide/GaN structure grown under optimized conditions.

Enhanced positive magnetoresistance effect in GaAs with nanoscale magnetic clusters

The enhanced positive magnetoresistance effect has been observed in GaAs containing nanoscale magnetic clusters. The ferromagnetic metallic clusters were embedded into GaAs by Mn ion implantation and rapid thermal annealing. Positive magnetoresistance in these structures has been observed and attributed to the enhanced geometric magnetoresistance effect in inhomogeneous semiconductors with metallic inclusions. The additional enhancement of positive magnetoresistance under light illumination is due to the higher mobility of photoexcited electrons in comparison with the mobility of holes in p-type GaAs prepared by Mn ion implantation.

Deep level emission of ZnO nanoparticles deposited inside UV opal

Abstract The temperature-dependent photoluminescence spectra of zinc oxide (ZnO) nanocrystals deposited inside the ultraviolet (UV) opal were studied. ZnO was grown in the voids between FCC packed SiO 2 spheres using spray pyrolysis under ultrasonic vibration in the solution containing a zinc nitrate precursor. The ZnO nanoparticles inside opal matrix with UV photonic band-gap exhibit suppression of the excitonic emission and enhancement of the deep level emission. Suppression of the excitonic lines is due to the inhibition of spontaneous emission, while enhancement and broadening of the DL emission in the green spectral region is due to Purcell effect. The infiltration of ZnO nanoparticles inside the photonic crystal may be a useful technique to increase its emission efficiency in the selected spectral region.

Origin of luminescence from Si−-implanted (11¯02) Al2O3

Cathodoluminescence (CL), photoluminescence, and transmission electron microscopy have been used to study the light-emitting and structural properties of (11¯02) sapphire implanted with 30-keV Si ions and subsequently annealed at temperatures up to 1100 °C. This procedure creates oriented Si crystallites with diameters in the range 4–5 nm together with extended defects parallel to the (0001) planes of (11¯02) Al2O3. Several CL bands found in Si−-implanted Al2O3(Al2O3:Si−) before and/or after annealing are compared with those from O−- and Al−-implanted samples. These and related experiments, including annealing temperature and implant dose dependence, suggest that a yellow CL band (2.16 eV/574 nm) from annealed Al2O3:Si− is nanocrystal related, while others are defect related.

Deep level defects in porous silicon

This paper reports on the existence of deep level defects in the band gap of porous silicon by the photo-induced current transient spectroscopy technique combined with the results of thermovoltage and conductivity measurements. The defects are found to exhibit deep donor levels in the upper part of the band gap. It is found that the thermal emission and ionization energies of the defect increase in the range from 0.29 to 0.86 eV below the conduction band edge as the porosity increases, and it is proposed that the defects play the role of a luminescence killer.

Optical and magnetic properties of Mn+-implanted neutron-transmutation-doped GaAs bulks

(Ga1−xMnx)As thin films with both semiconducting and magnetic properties were formed by using Mn+ ion implantation and thermal annealing with a goal of producing (Ga1−xMnx)As with a high ferromagnetic transition temperature Tc. Energy dispersive x-ray fluorescence measurements showed that the Mn+-implanted neutron-transmutation-doped (NTD) GaAs samples were (Ga1−xMnx)As thin films, and photoluminescence spectra showed that the annealed (Ga1−xMnx)As thin films were p-type semiconductors. The magnetization curve as a function of the magnetic field showed that ferromagnetism existed in the (Ga1−xMnx)As thin films, and the magnetization curve as a function of the temperature showed that the Tc was ≈140 K. The present results indicate that high-Tc (Ga1−xMnx)As thin films with both semiconducting and magnetic properties can be formed from NTD-GaAs bulks by using Mn+ implantation and annealing method.

Enhancement of a rectifying characteristic of InGaP diodes by hydrogenation

The effect of hydrogenation on electrical properties of InGaP epitaxy layers grown on GaAs has been investigated. It is found that hydrogenation using an infrared lamp heating at 200 °C can give rise to good rectifying characteristics on the Au/n-InGaP Schottky diode as well as to the passivation of defects. For the hydrogenated sample, the breakdown voltage increases to 35 from 4 V, the leakage current decreases by three orders of magnitude, and the saturation current increases about 100 times, relative to those for the untreated one. This characteristic is thought to result from the increase of the diode barrier height during hydrogenation. That is, the atomic hydrogen which diffuses into InGaP neutralizes the Si donor dopant as well as deep levels near the surface, resulting in the increase of the barrier height and the reduction of recombination centers.

Cathodoluminescence and Photoluminescence of Crystaline Silicon-Epilayer Grown on Si + -Implanted (1-102) Sapphire

Luminescence on Si-epitaxial layers grown on Si-implated Al 2 O 3 ( 1 1 02) with 30 keV Si + to a dose of 5×10 15 /cm 2 has been investigated. To active the implanted Si + ions in Al 2 O 3 , the post annealing was performed at 1100°C in Ar ambiant. Also, cathodoluminescence (CL) and photoluminescence (PL) have been used to study struc Al 2 O 3 tural and optical properties of nc-Si in the Si + -implanted (1 1 02) Al 2 O 3 substrates. In the PL and CL spectra for Si + -implanted samples, peaks to be responsible for nanocrystalline-Si (nc-Si) appear at 316 nm (3.92 eV) and 574 nm (2.16 eV), respectively. The crystallinity of nc-Si imbeded in Al 2 O 3 has been about 5nm in size and the dislocation aligned parallel to the (0001) planes of (1 1 02) Al 2 O 3 , confirmed by transmission electron microscopy (TEM).