Formation time optimization and evaluation of nanoporous GaN as an optically active medium for device applications

Nanoporous GaN (NP-GaN) embeds sub-nanoscale air gaps (n ≈ 1) that greatly expand refractive-index modulation for ultra-thin distributed Bragg reflectors (DBRs), boost surface area for photoelectrochemical (PEC) reactions, alleviate substrate lattice constraints to enable high-In red light emitting diodes (LEDs), and have even been applied in photovoltaic cells. Yet its use as an optically active medium is scarcely reported, making comprehensive evaluation of its optical and structural properties imperative for broader device integration. Herein, we report the potential of NP-GaN as an optically active medium for device applications by evaluating the optical and structural properties of NP-GaN samples etched for durations ranging from 5 to 15 min. Our results show that the average pore diameter does not increase significantly when the etching duration exceeds 10 min due to pore wall passivation by Ga-related byproducts. Meanwhile, the highest carrier lifetime and the strongest integrated near-band edge (NBE) intensity were observed in the NP-GaN sample etched for 10 min, which was attributed to pore branching. Overall, a 10 min etching duration, resulting in superior optical properties, was optimal for the formation of NP-GaN. With its advantages in optical properties with a higher active surface area compared to bulk thin films, NP-GaN optimization of etching duration provides insight into the realization of various device applications. This is not limited to GaN but extends to other nitrides such as InGaN and AlGaN, broadening the available bandgap range.