Nomura Ichirou

Abstract In this study, the growth behavior of Indium gallium nitride (InGaN)-based nanocolumn arrays was investigated, and red emission nanocolumn micro-light emitting diodes (μ-LEDs) were fabricated. The internal structure of the InGaN/GaN superlattice (SL) layer under the multiple-quantum-well (MQW) active layers was evaluated using scanning transmission electron microscopy (STEM) analysis. It was revealed that the InGaN crystal plane at the top of the nanocolumn changed from the c-plane, (1-102) plane, to the (10-11) plane as the number of SL pairs increased. A semipolar (10-11) plane was completely formed on top of the nanocolumn by growing InGaN/GaN SLs over 15–20 pairs, where the InGaN/GaN SL layers were uniformly piled up, maintaining the (10-11) plane. Therefore, when InGaN/AlGaN MQWs were grown on the (10-11) plane InGaN/GaN SL layer, the growth of the (10-11) plane semipolar InGaN active layers was observed in the high-angle annular dark field (HAADF)-STEM image. Moreover, the acute nanocolumn top of the (10-11) plane of the InGaN/GaN SL underlayer did not contribute to the formation of the c-plane InGaN core region. Red nanocolumn μ-LEDs with an φ12 μm emission window were fabricated using the (10-11) plane MQWs to obtain the external quantum efficiency of 1.01% at 51 A cm⁻². The process of nanocolumn μ-LEDs suitable for the smaller emission windows was provided, where the flat p-GaN contact layer contributed to forming a fine emission window of φ5 μm.

Conduction band discontinuity (ΔEc) of MgSe/ZnCdSe heterojunctions were evaluated using n–i–n diodes consisting of an undoped i-MgSe layer sandwiched by n-doped ZnCdSe layers. The n–i–n diodes were fabricated on InP substrates by molecular beam epitaxy. Injection current density versus applied voltage (J–V) characteristics of the n–i–n diodes were measured at 77 K and room temperature. In addition, the theoretical J–V characteristics of the n–i–n diode were calculated while varying ΔEc. By fitting the theoretical data to the experimental data, ΔEc was estimated to be 1.2 eV from the result at 77 K. This value is similar to the ΔEc estimated from the literature.

The application of indium tin oxide (ITO) as the p-cladding layer of II-VI compound semiconductor laser diodes (LDs) on InP substrates was investigated. The waveguide analysis of the LD structures revealed that the optical confinement effect around the active layer was obviously improved by changing the p-cladding layer from the conventional MgSe/BeZnTe superlattice to ITO. For example, the estimated optical confinement factors were 0.15 and 0.27 for the conventional and ITO LD structure, respectively, when the emission wavelength was 580 nm. In addition, we investigated optimum LD structures, considering the optical and carrier confinements at the active layer. In experiments, light emitting devices with an ITO layer were fabricated on InP substrates via molecular beam epitaxy and radio-frequency (RF) magnetron sputtering. Yellow emissions at 582 nm were observed by current injections at room temperature. These results indicate that ITO is a promising p-cladding layer material for II-VI LDs on InP substrates. (C) 2016 WILEY-VCH Verlag GmbH & Co.

II-VI-compound-semiconductor laser diode (LD) structures on InP substrates were investigated using device simulations and waveguide analysis. Our simulations showed that electron injection from the n-cladding into the active layer is hindered by the n-side barrier layer between the n-cladding and active layer. Consequently, holes are not injected into the active layer but instead leak to the n-side layers. It was shown that carrier injection efficiency can be improved by removing the n-barrier. On the contrary, no large differences were observed between the optical confinement factors of the LD structures with and without the n-barrier layer. In ex-periments, we have fabricated the LD structures with and without the n-barrier layer on InP substrates using molecular beam epitaxy. The turn-on voltage of the device without the n-barrier was smaller than that for the device with the n-barrier by about 5 V. Spontaneous orange emissions around 603 nm were observed for the devices without the n-barrier. In contrast, no emission was observed for the devices with the n-barrier. These results prove that the carrier injection into the active layer is enhanced by the removal of the n-barrier, leading to improved the device performances. (C) 2016 WILEY-VCH Verlag GmbH & Co.