Green-Light Nanocolumn Light Emitting Diodes With Triangular-Lattice Uniform Arrays of InGaN-Based Nanocolumns

Green-light nanocolumn light emitting diodes (LEDs) consisting of triangular-lattice uniform arrays of InGaN-based nanocolumns with lattice constants of 245-350 nm were fabricated with TiO₂ mask selective-area growth by RF-plasma-assisted molecular beam epitaxy. The built-in core/shell structure of InGaN/GaN multiple quantum wells was self-assembled, confining carriers in the core of the nanocolumns. The characteristics of the nanocolumn LEDs were evaluated at room temperature under dc current injection in the range from 4.5 to 450 A/cm². The emission wavelengths were 515 to 550 nm, and small current-induced spectral blueshifts of 2-11 nm were observed. The linewidth narrowing at a low current density was very small for the nanocolumn LEDs, in which nanocolumns with the same size were homogeneously arranged. The sidewalls of the nanocolumns were passivated by the deposition of Al₂O₃, contributing to the elimination of current leakage paths. The external quantum efficiency was improved with the passivation. Radiation beam angular profiles of the nanocolumn LEDs were evaluated and directional beam radiation was observed at specific wavelengths, which was attributed to the photonic band edge of the periodic nanocolumn arrangement.