Resonant photoemission of rare earth doped GaN thin films

Abstract

Abstract. The 4d → 4f Fano resonances for various rare earth doped GaN thin films (RE = Gd, Er, Yb) were investigated using synchrotron photoemission spectroscopy. The resonant photoemission Fano profiles show that the major Gd and Er rare earth 4f weight is at about 5-6 eV below the valence band maximum, similar to the 4f 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 4f 14 occupancy.

Rare earth 4f hybridization with the GaN valence band

“…As previously described, the RE x Ga 1-x N thin films (50-300 nm) were fabricated on Si(111) (RE = Yb, Gd) and sapphire, Al 2 O 3 (RE = Er) substrates by RF plasma (EPI 620) assisted molecular beam epitaxy (MBE) [23,31]. The growth parameters for the deposition of RE-doped (in situ) GaN thin films were a base pressure of ∼ 10 −11 Torr, nitrogen flux of 0.75-1.0 SCCM (Yb, Gd) and 2.0 SCCM (Er), RF power of 500 W, substrate temperature of 850-900 • C, Ga cell temperature of 850 • C and RE cell temperatures of 500-850 • C (Yb), 1000-1100 • C (Er) and 1050-1100 • C (Gd).…”

“…Atomically clean GaN:RE surfaces were obtained by several preparatory cycles of Ar + ion sputtering and annealing, as described elsewhere [23,31,32]. This will create a number of point defects, but photoemission is generally insensitive to such defects.…”

“…While numerous resonant photoemission studies of RE metals have been reported, the resonant processes resulting from photon interaction with III-nitride semiconductors are significantly less well understood. The 4d-4f photoemission resonances for various RE-doped GaN thin films (RE = Gd, Er, Yb) have now been reported [23]. Plucinski et al [24] reported a resonant photoemission process at the Ga 3p absorption threshold in GaN and compared the results to those reported for GaP and GaAs [25,26].…”

“…Resonant photoemission is a premier tool for identifying the occupied 4f positions of REs in the photoemission spectra of a semiconductor host [23,[27][28][29][30]48]. and Auger-like electrons emitted in a super Coster-Kronig process [52]…”

“…Additionally, Maruyama et al [27] reported on Eu:GaN using x-ray photoelectron spectroscopy (XPS) and resonant photoemission spectroscopy (RPES) and concluded, via 4d-4f resonant photoemission measurements, that the transition from trivalent to divalent Eu ions occurred near the surface of GaN. The key value of resonant photoemission, however, is to probe which valence bands of the semiconductor host have strong 4f and/or RE weight [23,[28][29][30]].…”