In this work, we demonstrated radical-enhanced atomic layer deposition (RE-ALD) as an ideal technique for incorporation of dopants in ultra-thin metal oxide films. The controlled doping of erbium in yttrium oxide is presented as a case study. Er-doped Y2(1)3 thin film is a potential waveguide core material for planar miniature optical amplifiers. Though SiO 2 has traditionally been used as the host material for Er ions in fiber amplifiers (∼20 meters long), it is an unsuitable host in small, compact amplifiers due to its low solubility for erbium. In contrast, Y 2O3 has a similar crystal structure and lattice constant as Er2O3, which in principle allows for a much higher concentration of Er to be incorporated, and hence higher gain values. The metal β-diketonates, Y(TMHD)3 and Er(TMHD)3, were used as the metal precursors and O radicals as the oxidant. The study of surface reaction kinetics in-situ using a quartz crystal microbalance (QCM) confirmed the self-limiting surface reactions in depositing pure Y2O 3 and Er2O3. Specifically, adsorption of the precursors was found to follow the Langmuir adsorption model. The O radicals not only create reactive sites for precursor adsorption but also effectively remove the β-diketonate ligands. Conformal deposition of stoichiometric and smooth metal oxide thin films with minimal carbon contamination was achieved at 300-330°C, confirmed by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Er-doped Y 2O3thin films were synthesized by depositing Y 2O3 and Er2O3 in an alternating fashion at 350°C. Specifically, the erbium doping level was effectively controlled by varying the ratio of Y2O3:Er 2O3 cycles during deposition, and a 20:1 ratio yielded ∼6 at.% Er in Y2O3. At 350°C, the films were found to be polycrystalline showing a preferential growth direction in the (111) plane. Room-temperature PL at 1.54 urn characteristic of the Er intra 4f transition was observed in a 500-Å Er-doped (6.6 at.%) Y2O 3 film deposited at 350°C. Well resolved Stark features indicated proper incorporation of Er in the Y2O3 host. The result is very promising, since the film is fairly thin and no annealing at high temperature is needed to activate the erbium ions. This suggested that radical-enhanced ALD was able to preserve the optically active trivalent state of the erbium ion from its precursor state. Significant PL quenching was observed in thin films incorporated with more than 12 at.% Er. Extended X-ray absorption fine structure (EXAFS) analysis showed an identical Er local environment in samples with 614% of Er, suggesting that the PL quenching observed at high Er concentration (>12 at.%) is likely dominated by ion-ion interaction and not by clustering. The effective absorption cross section for Er3+ ions incorporated in Y2O3 was determined to be ∼ 10-18 cm2, about three orders of magnitude larger than the direct optical absorption cross section reported for Er 3+ ions in a stoichiometric SiO2 host. These results validate Y2O3 as a promising Er host material and demonstrate that RE-ALD is a viable technique for synthesizing thin films with well-controlled dopant incorporation. Fabrication of planar optical amplifiers is currently underway to determine the fraction of optically active Er 3+ in Y2O3 and also the optical gain values for these devices.
|Number of pages||1|
|Publication status||Published - 2005|
|Event||05AIChE: 2005 AIChE Annual Meeting and Fall Showcase - Cincinnati, OH, United States|
Duration: 2005 Oct 30 → 2005 Nov 4
|Other||05AIChE: 2005 AIChE Annual Meeting and Fall Showcase|
|Period||05-10-30 → 05-11-04|
All Science Journal Classification (ASJC) codes