Optical activation of Eu ions in nanoporous GaN films

摘要

A systematic optical activation study of Eu-implanted nanoporous GaN films has been carried out as a function of ion dose and annealing temperature. The nanoporous GaN films are prepared by photoelectrochemical etching of n-type GaN films in HF-based electrolyte. Eu ions are implanted in both n-type GaN and n-type porous GaN films at 200 keV with doses ranging from 5 x 10~(14) to 5 x 10~(15) cm~(-2). For the implantation damage recovery and optical activation of Eu~(3+) ions, rapid thermal annealing is performed in the temperature range of 900-1200℃ under nitrogen ambient. The surface morphology of implanted porous GaN after different processing steps is characterized by scanning electron microscopy and the results show that porous morphology remains uniform even after ion implantation and high temperature processing. Microphotoluminescence and micro-Raman techniques have been used to investigate the optical properties of these Eu-implanted nanoporous films. Postimplantation annealing of both as-grown GaN and porous GaN films leads to the observation of strong photoluminescence (PL) peak around 622 nm, which is associated with the ~5D_0-~7F_2 intraionic transition of Eu~(3+) ions. We have observed that PL intensity of Eu-related luminescence peaks increases with annealing temperature up to 1100℃. In addition, due to efficient light extraction by surface nanostructuring, Eu-implanted porous GaN films show much stronger luminescence when compared to Eu-implanted as-grown GaN. Raman spectral analyses also indicate the optimum annealing condition for the implantation damage recovery and the compressive stress state in the Eu-implanted films.