SiO₂ nanohole arrays with high aspect ratio for InGaN/GaN nanorod-based phosphor-free white light-emitting-diodes

Vertically aligned InGaN/GaN nanorod (NR)-based phosphor-free light emitting diodes (LEDs) using SiO₂ nanohole patterns are demonstrated. The highly ordered SiO₂ nanoholes were realized on a 2 μm-thick n⁺GaN template by a two-step dry etching process. The use of C₄F₈/O₂/Ar plasma chemistries under the low pressure is found to greatly enlarge the bottom diameter of each hole, exhibiting high aspect ratio (AR ∼ 9) and vertical etch profile (∼89°). SAG technique was used to define the height of the GaN NRs while the width is determined by the trimethylgallium flow rate and growth temperature. An LED structure consisted of three-pairs of InGaN/GaN quantum well and AlGaN electron blocking layer on the sidewall of the nanorod in a core-shell structure. The wavelengths were successfully tuned by controlling pitches of the rods, which was caused by the different growth rate and indium incorporation of conformally overgrown InGaN multiquantum wells. At the operating current density of 1.5 A/cm² (65 mA), NR-based single-chip phosphor-free white LEDs with the dimension of 630 × 970 μm² show highly stable white emission characteristics which are attractive for future solid-state lighting and full-color display applications.