Control of Location and Carrier-Interaction of Erbium Using Erbium-Doped Si/SiO 2 Superlattice
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as well. Such problems, however, may be solved by using Si/Si0 2 superlattices instead. By directly depositing erbium-doped Si/Si0 2 superlattices, one can control not only the thickness, and thus the magnitude of the quantum confinement effect, of the Si layers accurately, but also the location of erbium atoms (in Si layers, in SiO 2 layers, or at the interface) as well. Furthermore, such Si/SiO 2 superlattices are expected to be much more amenable to a controlled current transport than silicon nanoclusters dispersed randomly in an insulating matrix. In this paper, we investigate the effects of such control on the Er3+ photoluminescence (PL) properties of erbium-doped Si/Si0 2 superlattices. We find that controlling the location of the erbium atoms is crucial for controlling the Er 3+ luminescence, and identify controlling the interaction between erbium atoms and the carriers in the Si layer to be the key point. Based on this identification, we demonstrate that isolating the erbium atoms from the Si layers by depositing thin buffer layers of pure Si0 2 improves the Er3+ photoluminescence by several orders of magnitude while still allowing efficient excitation by carriers to dominate. Finally, we demonstrate fabrication of efficient waveguides using such erbium doped Si/Si0 2 superlattices. EXPERIMENT Er doped Si/Si0 2 superlattices were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) of SiH 4 and 02 with concurrent sputtering 27 Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
of Er and subsequent rapid thermal anneal. A sequence of 600 'C, 950 °C, and 600 °C for 20, 5, and 5 min was used to avoid cracking and spalling of the film. Different layers were deposited by first extinguishing the plasma, changing the gas flow rate, and then re-igniting the plasma. Films were characterized by both Rutherford backscattering spectroscopy (RBS), medium energy ion-scattering spectroscopy (MEIS) and cross-sectional transmission electron microscopy (TEM). 2 MeV He++ ions were used for RBS, and 101.2 keV H+ ions were used for MEIS. 1.54 jIm Er 3+ PL spectra were measured using the 477 line of Ar laser, a thermoelectircally cooled InGaAs detector and the lock-in technique. 477 nm line was chosen to ensure that excitation of Er3+ ions are all carrier-mediated, since it does not coincide with the optical absorption bands of Er 3+ ions. Strip waveguides were fabricated by the standard Si0 2 plasma-etch using Ar/CF 4 plasma. RESULTS AND DISCUSSION Recently, we have investigated the 1.54 jim Er 3÷ PL from erbium-doped Si/Si0 2 superlattices in which erbium was doped either into the Si layers or the SiO 2 layers only [8]. We found that the excitation of Er3 + ions was mediated by carriers, and that the film which had erbium atoms doped only into the Si0 2 layers had more intense 1.54 gim Er3+ PL with less temperature quenching of the Er3+ PL. Thus, we have concluded that excitation by carriers can occur even when the carriers are some atomic distances away, and that
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