The rare earth 4$f$ hybridization with the GaN valence band
POSTER
Abstract
The placement of the Gd, Er, and Yb 4f states within the GaN valence band has been explored by both experiment and theory. The 4$d$ -- 4$f$ photoemission resonances for various rare earth doped GaN thin films (RE $=$ Gd, Er, Yb) provide an accurate depiction of the occupied 4$f$ state placement within the GaN. The resonant photoemission show that the major Er and Gd rare earth 4$f$ weight is at about 5-6 eV below the valence band maximum, similar to the 4$f$ weights in the valence band of many other rare earth doped semiconductors. For Yb, there is very little resonant enhancement of the valence band of Yb doped GaN, consistent with a largely 4$f^{\mathrm{14-\delta }}$ occupancy. The placement of the rare earth 4$f$ levels is in qualitative agreement with theoretical expectations.