Spectroscopic studies of the visible and infrared luminescence from Er doped GaN

The visible and infrared luminescence of erbium doped gallium nitride prepa red by metal-organic molecular beam epitaxy (MOMBE) and solid-source molecu lar beam epitaxy (SSMBE) were investigated as a function of excitation wave length and temperature. Both samples exhibited 1.54 mum Er3+ photoluminesce nce (PL), but only GaN:Er (SSMBE) showed visible PL lines at 537 and 558 nm . Excitation wavelength dependent PL measurements revealed the existence of multiple Er sites leading to an inhomogeneous line broadening of the Er3intra-4f PL under above-gap pumping. A significant narrowing of the green E r3+ PL lines was observed when pumping resonantly into an intra-4f transiti on. This observation suggests that a specific class of Er3+ ions was select ively excited. A temperature dependent study of the PL intensity ratio and lifetime of the green Er3+ lines revealed that the two excited states H-2(1 12) and S-4(3:2) are thermally coupled. Considering this thermal coupling a nd assuming that non-radiative decay is negligibly small at low temperature s, the green luminescence efficiency at room temperature was estimated to b e near unity. (C) 2001 Elsevier Science B.V. All rights reserved.