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

The visible and infrared luminescence of erbium doped gallium nitride prepared by metal-organic molecular beam epitaxy (MOMBE) and solid-source molecular beam epitaxy (SSMBE) were investigated as a function of excitation wavelength and temperature. Both samples exhibited 1.54 μm Er3+ photoluminescence (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 Er3+ intra-4f PL under above-gap pumping. A significant narrowing of the green Er3+ PL lines was observed when pumping resonantly into an intra-4f transition. This observation suggests that a specific class of Er3+ ions was selectively excited. A temperature dependent study of the PL intensity ratio and lifetime of the green Er3+ lines revealed that the two excited states 2H11/2 and 4S3/2 are thermally coupled. Considering this thermal coupling and assuming that non-radiative decay is negligibly small at low temperatures, the green luminescence efficiency at room temperature was estimated to be near unity.