Electroluminescence from silicon-based light-emitting devices with erbium-doped TiO_2 films annealed at different temperatures

摘要

We have previously developed silicon-based light-emitting devices (LEDs) with luminescent erbium (Er)-doped TiO_2 (TiO_2:Er) films [Yang et al., Appl. Phys. Lett. 100, 031103 (2012)]. In an LED therein, the TiO_2:Er film is sandwiched between the ITO film and heavily boron-doped p-type silicon (p~+-Si). In this work, we have investigated the electroluminescence (EL) from two LEDs with the TiO_2:Er films annealed at 650 and 850 °C, respectively. It is revealed that between the TiO_2:Er film and p~+-Si, there is an intermediate silicon oxide (SiO_x, x ≤ 2) layer and its thickness increases from ∼4 to 8 nm with the increase of annealing temperature from 650 to 850 °C. Interestingly, the thickness of the intermediate SiO_x layer is found to exhibit a profound impact on the EL from the LED with the TiO_2:Er film on p~+-Si. The EL from the LED with the 650 °C-annealed TiO_2:Er film is activated only under the forward bias with the positive voltage connecting to the p~+-Si substrate. Such EL consists of the oxygen-vacancy-related emissions from TiO_2 host and the characteristic visible and ∼1540 nm emissions from the Er~(3+) ions, while the EL from the LED with the 850 °C-annealed TiO_2:Er film can only be enabled by the reverse bias with the negative voltage applied on the p~+-Si substrate. Such EL features only the visible and ∼1540 nm emissions from the Er~(3+) ions. The difference in the EL behaviors of the two LEDs as mentioned above is found to be ascribed to the different electrical conduction mechanisms.