Energy-transfer upconversion in Al₂O₃:Er³⁺ thin layers

Erbium-doped aluminum oxide (Al2O3:Er) is a promising material for integrated amplifier or tunable laser applications due to its wide gain spectrum around 1550 nm. We deposited Al2O3 layers on thermally oxidized Si-wafers by reactive co-sputtering at 550°C. Propagation losses were 0.11 dB/cm at λ =1.5 μm. Channel waveguides were fabricated by reactive ion etching with propagation losses down to 0.21 dB/cm. Under pumping at 977 nm, the optical small-signal gain at 1533 nm is 0.84 dB/cm, resulting in 5.4 dB net gain over the waveguide length of 6.4 cm. Net gain is obtained over a wavelength range of 41 nm. The Er concentration was measured using Rutherford Back-Scattering (RBS). Lifetimes of the 4I13/2 level of up to 7 ms were measured for Er concentrations around 2×1020 cm-3. A faster decay with an increasingly non-exponential initial component is measured for higher Er concentrations (Fig. 2). While the initial quenching is probably due to migration-accelerated energy-transfer upconversion between neighboring Er3+ ions in the 4I13/2 level, the decreasing exponential tail is due to either pair-induced energy-transfer upconversion or quenching by impurity ions. Detailed investigations of the quenching mechanisms are currently under way.