Rie Togashi

Abstract A red InGaN-based nanocolumn micro μLED with an emission diameter of ϕ2.2 μm was demonstrated to achieve an on-wafer external quantum efficiency (EQE) of 2.1% at the peak wavelength of 615 nm. The LED was fabricated by repeating the electrode process on the same nanocolumn pattern area and reducing the emission diameter from ϕ80 to ϕ2.2 μm. The peak EQE, which was maximized at ∼25 A cm⁻², increased by decreasing the emission diameter from 1.2% to 2.1%. This behavior, which differs from that of InGaN-film LEDs, is characterized as a unit of independent nano-LEDs with passivated sidewalls of nanocolumn LEDs.

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.

Thermodynamic analyses for the growth of group-III sesquioxides, including alpha-Al2O3, ss-Ga2O3, and c-In2O3, by both ozone and plasma-assisted MBE were performed. In either case, under O-rich conditions, the driving force for III2O3 (III = Al, Ga, In) growth (Delta P-III2O3) increased with increasing input partial pressure of the group-III metal (P-III(o)), without generation of metal droplets. Conversely, under group-III-metal-rich conditions, Delta(PIII2O3) decreased with increasing P-III(o) and/or decreasing input partial pressure of O-3 or O. This decrease was caused by the formation of Ga2O or In2O during growth of ss-Ga2O3 and c-In2O3. The decrease of Delta P-Al2O3D was smaller because the equilibrium constant of alpha-Al2O3 formation reaction was very large. Ga and In droplets formed at low temperatures (<420 degrees C), whereas Al droplets were formed at high temperatures (<820 degrees C), and the order that enabled growth at higher temperatures was c-In2O3 < ss-Ga2O3 << alpha-Al2O3. (c) 2023 The Japan Society of Applied Physics

Abstract Thermodynamic analyses of β-Ga₂O₃ growth by both ozone and plasma-assisted molecular beam epitaxy were performed. In either case, the growth mechanism was found to differ depending on whether the input VI/III ratio was above or below 1.5. Under O-rich conditions (VI/III &gt; 1.5), the driving force for β-Ga₂O₃ growth (ΔP_Ga2O3) was determined to increase linearly with increasing Ga input partial pressure (P°_Ga) because almost all the supplied Ga was used for growth of the β-Ga₂O₃. In contrast, Ga-rich conditions (VI/III &lt; 1.5) caused ΔP_Ga2O3 to decrease. Etching of the β-Ga₂O₃ occurred with increasing P°_Ga due to the formation of volatile Ga₂O. This work also demonstrated that the use of ozone allowed growth at higher temperatures than the use of O radicals. The calculated results were in good agreement with experimental values, indicating that β-Ga₂O₃ growth by molecular beam epitaxy can be explained by thermodynamics.