Vertical nanoporous GaN substrates for photonic engineering: Lu2O3:Eu single crystal thin films as an example

Abstract

To improve the efficiency of light extraction, the vertical-oriented nanoporous (NP) GaN film as scattering medium as well as light-coupling component was prepared by electrochemical (EC) etching followed by annealing process. The Lu2O3:Eu film as fluorescence medium was deposited on the NP-GaN substrate via pulse laser deposition (PLD) method, which has out-of-plane epitaxial relationship of Lu2O3 (222) || GaN (0002). By changing etching and annealing conditions, the average pore diameter, pore density and pore sidewall roughness of NP-GaN are controlled. The experiment shows that the photoluminescence (PL) intensities and quantum efficiencies of epitaxial films are related to the pore density and sidewall roughness of NP-GaN substrates. Due to the scattering effect of nanopores and light-coupling inside Lu2O3:Eu films on the NP-GaN substrates, the PL intensities were enhanced 13–96% compared with that of the films on as-grown GaN substrates, although the crystal quality of the epitaxial film becomes worse with the increase of porosity of the substrates.