Analysis of the spectra of trivalent erbium in multiple sites of hexagonal aluminum nitride

The 12 K cathodoluminescence spectra of Er super(3+) doped into single crystals of aluminum nitride (2H-AlN) in the hexagonal phase are reported between 320 nm and 775 nm. The emission spectra represent transitions from the lower Stark level of super(2)P sub(3/2) to the Stark levels of the super(4)I sub(15/2), super(4)I sub(13/2>), super(4)I sub(11/2>), super(4)I sub(9/2), super(4)F sub(9/2), and super(4)S sub(3/2) multiplet manifolds of Er super(3+)(4f super(11)). Emission spectra from super(4)S sub(3/2) to super(4)I sub(15/2) are also reported. All observed strong line emission are accounted for in terms of two principle sites, denoted site "a" and site "b", with a few line spectra attributed to additional sites. A parameterized Hamiltonian that includes the atomic and crystal-field terms for Er super(3+)(4f super(11)) super(2S+1) L sub(J) was used to determine the symmetry and the crystal field splitting of the "a" and "b" sites. A descent in symmetry calculation was carried out to determine if distortion due to the size difference between Er, Al and the vacancies can be discerned. Modeling results assuming C sub(3v) and C sub(1h) are discussed. It appears that the sensitivity to a C sub(1h), model is not sufficient to invalidate the choice of C sub(3v) as an approximate symmetry for both sites. The g-factors reported from an EPR study of Er super(3+) in single-crystal AlN are in reasonable agreement with calculated g-factors for Er super(3+) in the "a" site assuming C sub(3v) symmetry.