Effect of KOH passivation for top-down fabricated InGaN nanowire light emitting diodes

Gallium nitride (GaN) nanowire (NW) light emitting diodes (LEDs) are promising candidates for microdisplay applications due to smaller dimensions and potential for novel integration approaches. For the commonly adopted top-down GaN NW fabrication, the required dry etching steps tend to result in surface states, leading to reduced radiative recombination rates in LEDs. To passivate the surface and tune the diameter of the NWs, hydroxyl-based chemicals such as potassium hydroxide (KOH) are widely used to treat the surface of these nanostructures. However, studies on the effects of temperature, concentration, and the damage recovery aspects of hydroxyl etching of GaN NWs are very scarce. These etching parameters are of great importance for device performance. Here, these effects are explored thoroughly with a focus on the correlation of InGaN/GaN NW LED performances to KOH etching temperature, concentration, and time, together with a fundamental crystallographic analysis. The KOH concentration resulting in total removal of the NW base tapering and a collimated etch profile for InGaN NW LEDs was found to be 0.8 wt. % at a temperature of 45 °C. A 20 min etch at 23 °C with a 0.1 wt. % KOH concentration will remove surface states from a top-down fabricated NW LED to recover up to 90% of the peak photoluminescence (PL) intensity lost by the dry etch step. The oscillation behavior in PL intensity with regard to the KOH etch time has been demonstrated in InGaN/GaN NW LEDs for the first time, which will shed light upon the design and passivation of these devices for microdisplays.