EXCITATION MECHANISMS OF MULTIPLE ER3-IMPLANTED GAN( SITES IN ER)

Site-selective photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies carried out at 6K on the similar to 1540 nm I-4( 13/2) --> I-4(15/2) emissions of Er3+ in Er-implanted GaN have reveale d the existence of four different Er3+ sites and associated PL spectra in this semiconductor. Three of these four sites are excited by below -gap, impurity-or defect-related absorption bands, with subsequent non radiative energy transfer to the Er3+ 4f electrons; a fourth site is e xcited by direct Er3+ 4f shell absorption. PLE spectra obtained by sel ectively detecting Er3+ PL from each of the three sites pumped by broa d below-gap absorption bands are compared with the PLE spectra of broa d PL bands attributed to implantation damage-induced defects in the Er -implanted GaN. This comparison enables us to distinguish broad-band, below-gap optical excitation processes for Er3+ emission that are attr ibutable to (1) absorption due to implantation damage-induced defects; (2) absorption due to defects or impurities characteristic of the as- grown GaN film; and (3) an Er-specific absorption band just below the band gap which may involve the formation of an Er-related isoelectroni c trap. The two sites excited by impurity-or defect-related absorption bands are also strongly pumped by above-gap excitation, while the sit es pumped by the Er-related trap and direct 4f shell absorption are no t. This observation indicates that excitation of Er3+ luminescence in crystalline semiconductor hosts by either optical or electrical inject ion of electron-hole pairs is dominated by trap-mediated carrier captu re and energy transfer processes. These trap-mediated processes may al so control the thermal quenching of Er3+ emission in semiconductors.