We demonstrated that the tetramethylammonium hydroxide (TMAH) solution possesses different etching abilities to the chip sidewalls with different orientations because the orientation of chip sidewall determines the exposed crystallographic plane of gallium nitride (GaN) and these crystallographic planes are with different chemical stability to the TMAH solution. After TMAH etching treatment, trigonal prisms were observed on sidewalls where m-plane GaN was exposed. For the investigated two types of light-emitting diodes (LEDs) with orthogonal arrangements, the LEDs with their larger sidewalls orientated along the [11⁻20] direction exhibited an additional 10% improvement in light output power after TMAH etching treatment compared to the LEDs with larger sidewalls orientated along the [1⁻100] direction.
Keywords: GaN-based UV LED; crystal orientation; light extraction; prism-structured sidewall; wet chemical etching.