III-nitride semiconductor-based light-emitting diodes (LEDs) have superior physical properties, such as high thermal stability and brightness, for application to solid-state lighting sources. With the commercialization of GaN-based LEDs, improving LED reliability is important because they can be affected by electrostatic discharge, reverse leakage, and breakdown. However, research on the reverse bias characteristics of GaN-based LEDs is insufficient. We studied the reverse breakdown mechanism and demonstrated that a local breakdown can form a conductive channel in GaN-based LEDs, which can be expanded to a novel planar-type LED structure without an n-contact electrode. Furthermore, we found that this approach can be applied to AC-controllable light-emitting devices without any AC–DC converter.

Flat-type InGaN-based light-emitting diodes (LEDs) without an n-type contact electrode were developed by using a local breakdown conductive channel (LBCC), and the effect of the In content of the InGaN quantum wells (QWs) on the local breakdown phenomenon was investigated. Electroluminescence and X-ray analyses demonstrated that the homogeneity and crystallinity of the InGaN QWs deteriorated as the In content of the InGaN QWs increased, thereby increasing the reverse leakage current and decreasing the breakdown voltage. After reverse breakdown with a reverse current of several mA, an LBCC was formed on the GaN-based LEDs. The surface size and anisotropic shape of the LBCC increased as the indium content of the InGaN QWs in the LEDs increased. Moreover, a flat-type InGaN LED without an n-type electrode was developed by using the LBCC. Notably, the resistance of the LBCC decreased with increasing indium content in the InGaN QWs, leading to lower resistance and higher light emission of the flat-type InGaN-based LEDs without an n-type contact electrode.

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We studied the thickness dependence of the crystallographic and optical properties of ZnO thin films grown on c-plane sapphire substrate using atomic layer deposition. High-resolution X-ray diffraction (HR-XRD) revealed two peaks at 34.5° and 36.2° in the initial growth stage of ZnO on the sapphire substrate, corresponding to the (002) and (101) ZnO planes, respectively. However, as the thickness of the ZnO film increased, the XRD intensity of the (002) ZnO peak increased drastically, compared with that of the (101) ZnO peak. This indicated that (002) and (101) ZnO were simultaneously grown on the c-plane sapphire substrate in the initial growth stage, and that (002) ZnO was predominantly grown with the increase in the thickness of ZnO film. The ZnO thin film presented an anisotropic surface structure at the initial stage, whereas the isotropic surface morphology was developed with an increase in the film thickness of ZnO. These observations were consistent with the HR-XRD results.