Local structure and bonding of luminescent Er in GaN: a contrast with Er in Si

X-ray absorption measurements from relatively high concentrations of Er (>0.1 at. percent) doped in GaN films show that Er occupies the Ga site with an unprecedentedly short Er-N bond length. Electroluminescence intensities from these GaN:Er films correlate with the concentration of Er atoms that replace Ga, not with the abundantly present O impurities in the host. Simple chemical concepts are used to explain each of these results and their striking difference from those obtained for Er-doped Si.