부산대학교 도서관

Site-selective photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies carried out at 6K on the [proportional to]1540 nm 4.sup.I.sub.13/2[right arro[w].sup.4]I.sub.15/2 emissions of Er.sup.3+ in Er-implanted GaN have revealed the existence of four different Er.sup.3+ 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 nonradiative energy transfer to the Er.sup.3+ 4f electrons a fourth site is excited by direct Er.sup.3+ 4f shell absorption. PLE spectra obtained by selectively detecting Er.sup.3+ PL from each of the three sites pumped by broad below-gap absorption bands are compared with the PLE spectra of broad 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 Er.sup.3+ emission that are attributable 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 isoelectronic trap. The two sites excited by impurity-or defect-related absorption bands are also strongly pumped by above-gap excitation, while the sites pumped by the Er-related trap and direct 4f shell absorption are not. This observation indicates that excitation of Er.sup.3+ luminescence in crystalline semiconductor hosts by either optical or electrical injection of electron-hole pairs is dominated by trap-mediated carrier capture and energy transfer processes. These trap-mediated processes may also control the thermal quenching of Er.sup.3+ emission in semiconductors.