Keun-Man Song

Effect of Barrier Thickness on the Interface and Optical Properties of InGaN/GaN Multiple Quantum Wells

We investigated the effect of barrier thickness on the interfacial and optical properties of the InGaN/GaN multiple quantum wells (MQWs) grown in a low-pressure metalorganic chemical vapor deposition system. The GaN barrier thickness in the InGaN/GaN MQWs was found to play a key role to determine the interfacial structural and optical characteristics of the MQWs. As the thickness of the GaN barrier layer was increased, the abruptness of the interface between InGaN and GaN layers deteriorated, probably due to the generation of defects induced by the strain accumulation in the MQWs. Accordingly, the intensity and the line-width of the photoluminescence taken from the MQWs were reduced and broadened, respectively with the increase of the GaN barrier thickness. The InGaN/GaN MQWs grown with an optimized barrier thickness showed an intense room-temperature photoluminescence at the wavelength of 479.5 nm with a very narrow full width at half maximum of 40.82 meV.

Structural and optical properties of InGaN/GaN multiple quantum wells: The effect of the number of InGaN/GaN pairs

The effect of the number of InGaN/GaN quantum well (QW) pairs on the interfacial structural and optical properties of InGaN/GaN multiple quantum wells (MQWs), as grown by low-pressure metalorganic vapor-phase epitaxy was examined. As the number of QW pairs increased, In-rich InGaN precipitates were more readily detected in the InGaN/GaN MQWs by cross-sectional transmission electron microscope. The intensity of the photoluminescence (PL) peak was decreased and the PL peak was red-shifted with an increase in the number of QW pairs. X-ray diffraction measurements revealed that the interfacial structure between InGaN and GaN were also deteriorated with the increasing number of QW pairs. These results can be attributed to the relaxation of an accumulated strain through the dislocations induced by an increase in the total thickness of the MQWs with an increase in the number of QW pairs. These results suggest that the defects such as dislocations facilitate the formation of In-rich phases in the InGaN layers in the MQWs.

Effect of growth interruption and the introduction of H2 on the growth of InGaN/GaN multiple quantum wells

The effects of the growth interruption and the introduction of H2 during interruption time on the optical and structural properties of InGaN/GaN multiquantum wells (MQWs), grown by metalorganic chemical vapor deposition, were investigated. When the growth was interrupted during the formation of interfaces in the MQWs, the intensity of photoluminescence (PL) was greatly increased and the formation of InN-rich regions near the surface of the InGaN well layer was suppressed. As the interruption time increased, however, the PL intensity decreased and the average In composition of InGaN/GaN MQWs decreased. When H2 was introduced during the growth interruption, the intensity of the PL was significantly enhanced by eliminating the impurities at the interface and the PL peaks were blueshifted due to the reduction in the thickness of the InGaN well layers, as a result of H2 etching of well and barrier layers.

Characteristics of indium incorporation in InGaN/GaN multiple quantum wells grown on a-plane and c-plane GaN

We investigated the characteristics of InGaN-based multiple quantum wells (MQWs) grown on a-plane and c-plane GaN templates, which were grown by metal-organic chemical vapor deposition onto r-plane and c-plane sapphire, respectively. A shorter photoluminescence peak wavelength and peaks with larger full-width at half-maximum are observed for MQWs grown on an a-plane GaN template compared with a c-plane GaN template, despite the same growth conditions used. A growth model based on the atomic configuration of the growing surfaces is proposed to explain the difference in optical emission properties and indium incorporation between a-plane and c-plane MQWs.

Ohmic contact to nonpolar a-plane p-type GaN using Ni/Au

In this study, we examined the characteristics of Ni/Au (20 nm/80 nm) ohmic contacts to non-polar a-plane p-GaN as a function of annealing temperature. The current?voltage (I?V) curves were showed an upward curve with annealing when Ni/Au metals were used as ohmic metals to nonpolar p-GaN, which was similar to those of the other crystalline planes. The contact resistivity decreased from 2.36 to 6.95 ? 10?3 ? cm2. Secondary ion mass spectroscopy showed that the Ga atoms out-diffused from the GaN substrate after annealing at 400 ?C, which led to the generation of Ga vacancies. The formation of Ga and N vacancies was found to be a competing process during annealing.