Influence of the Annealing Ambient on Structural and Optical Properties of Rare Earth Implanted GaN

Abstract

GaN films were implanted with Er and Eu ions and rapid thermal annealing was performed at 1000, 1100 and 1200 ºC in vacuum, in flowing nitrogen gas or a mixture of NH 3 and N 2 . Rutherford backscattering spectrometry in the channeling mode was used to study the evolution of damage introduction and recovery in the Ga sublattice and to monitor the rare earth profiles after annealing. The surface morphology of the samples was analyzed by scanning electron microscopy and the optical properties by room temperature cathodoluminescence (CL). Samples annealed in vacuum and N 2 already show the first signs of surface dissociation at 1000 ºC. At higher temperature, Ga droplets form at the surface. However, samples annealed in NH 3 +N 2 exhibit a very good recovery of the lattice along with a smooth surface. These samples also show the strongest CL intensity for the rare earth related emissions in the green (for Er) and red (for Eu). After annealing at 1200 ºC in NH 3 +N 2 the Eu implanted sample reveals the channeling qualities of an unimplanted sample and a strong increase of CL intensity is observed.

Strong Room Temperature Blue Emission from Rapid Thermal Annealed Cerium-Doped Aluminum (Oxy)Nitride Thin Films

“…The top layer (about 35 nm thick) exhibits granular crystallites with oxygen content ∼20%, as determined by fitting the RBS spectrum of Figure , while the bottom layer is columnar with less than 1% of oxygen. A similar surface modification phenomenon in post-deposition annealed films has been reported previously in RE-doped GaN . It was attributed to the release of N surface atoms out of the sample during the annealing at high temperature (above 800 °C) leaving N vacancies that could cluster to form voids and change the crystal structure.…”

“…A similar surface modification phenomenon in post-deposition annealed films has been reported previously in RE-doped GaN. 30 It was attributed to the release of N surface atoms out of the sample during the annealing at high temperature (above 800 °C) leaving N vacancies that could cluster to form voids and change the crystal structure. In addition, at high annealing temperature the partial pressure of residual oxygen inside the oven significantly increased.…”

Optical and structural studies in Eu-implanted AlN films

“…The samples annealed at 1100 • C in N 2 or N 2 + NH 3 show similar f s , but the PL intensity is higher for the annealing in N 2 + NH 3 . An increase of luminescence intensity for annealing in a N 2 + NH 3 atmosphere, as compared to N 2 annealing, was also observed for Eu-implanted GaN [7]. It might be due to the incorporation of hydrogen into the sample, which was shown to increase the luminescence intensity in Er-doped AlN [13].…”

“…It was also intensively studied as a technique for doping GaN with RE ions (e.g. [5][6][7][8]). The recovery of the crystal and optical activation was found to depend strongly on the annealing conditions [7].…”

“…[5][6][7][8]). The recovery of the crystal and optical activation was found to depend strongly on the annealing conditions [7]. Thin AlN layers were used as protective capping on GaN preventing the surface amorphisation of GaN and allowing the use of higher annealing temperatures [8].…”