Site-Selective Photoluminescence Spectroscopy of Er-Implanted Wurtzite Gan Under Various Annealing Conditions

Abstract

ABSTRACTThe ˜1540 nm 4I13/2 → 4I15/2 emissions of Er3+ in Er-implanted GaN annealed at temperatures in the 400 to 1000 °C range were investigated to gain a better understanding of the formation and dissociation processes of the various Er3+ sites and the recovery of damage caused by the implantation with increasing annealing temperature (TA). The monotonic increase in the intensity of the broad defect photoluminescence (PL) bands with increasing TA proves that these are stable radiative recombination centers introduced by the implantation and annealing process. These centers cannot be attributed to implantation-induced damage that is removed by postimplantation annealing. Selective wavelength pumping of PL spectra at 6 K reveals the existence of at least nine different Er3+ sites in this Er-implanted semiconductor. Most of these Er3+ PL centers are attributed to complexes of Er atoms with defects and impurities which are thermally activated at different TA. Only one of the nine observed Er3+ PL centers can be pumped by direct 4f absorption and this indicates that it is the highest concentration Er3+ center and it represents most of the optically active Er3+ in the implanted sample. The fact that this Er3+ center cannot be strongly pumped by above-gap light or broad band below-gap absorption indicates that it is an isolated center, i.e. not complexed with defects or impurities. This 4f-pumped PL spectrum appears at annealing temperatures as low as 400°C, and although its intensity increases monotonically with increasing TA, the wavelengths and linewidths of its characteristic peaks are unaltered. The observation of this high quality Er3+ PL spectrum at low annealing temperatures illustrates that the crystalline structure of GaN is not rendered amorphous by the ion implantation. The increase of the PL intensities of the various Er3+ sites with increasing TA is due to the removal of competing nonradiative channels with annealing.