Er-doped In 0.5 Al 0.5 P native oxides on GaAs: photoluminescence characterization and annealing optimization

Abstract

Er-doped waveguide amplifiers (EDWA) require high doping levels due to their length limit of a few to tens of cm, making the host selection of great importance to avoid deleterious high concentration effects. The wet thermal oxides of InAlP (lattice matched to GaAs) are phosphate rich, making them an attractive rare earth host for EDWAs where monolithic integration of pump lasers may be possible. InAlP epilayers are partially oxidized in water vapor (4 h, 500 °C). Er-implantation (300 keV, 10 15 cm -2 total dose) performed either before or after growth of the 300 nm thick oxide results in a peak Er concentration of ~10 20 cm -3 . Room temperature photoluminescence (PL) characterization shows broad (61 nm FWHM) emission with a long 8 ms lifetime. We present a comparison of PL characteristics of Er-doped InAlP and AlGaAs native oxides, and results of rapid thermal processor (RTP) annealing studies for host optimization. At 683 °C, the 3 sec optimal annealing time for post-oxidation-implanted samples is notably shorter than that of the preoxidation-implanted samples (20 sec), indicating less thermal energy is required for Er. A spectral line shape change is also observed for the post-oxidation-implanted samples when over-annealed, indicating a host phase change and local environment change for Er ions. For both post-and pre-oxidation-implanted samples, PL lifetimes remain near 8 ms after RTP annealing over the entire temperature range of 500 °C to 800 °C, indicating minimal Er clustering and suggesting that even higher Er concentrations, desirable for increased EDWA gain, are possible.