Photoluminescence and Crystal Structure of Eu Doped Silicon Oxide Prepared By Hybrid Sputtering and ECR-PECVD

Abstract

Silicon based light emitters have attracted a considerable interest due to its potential application in emerging technology in the field of solid-state lightening (SSL), solar cells, light emitting diodes (LEDs) and displays. Sharp and well-defined, 4f transition emission of rare earth (RE) elements drive RE doping to be one of the major approaches for enhancing the optical properties of silicon-based materials and it has drawn a significant attention over the last few decades [1]. Cerium (Ce) and terbium (Tb) correspond to blue and green light emission, respectively, and they have been developed to some extent. However, achieving the red-light emission which attributes to the trivalent europium (Eu) oxidation state is more challenging due to the change between the two oxidation states of Eu (Eu2+ and Eu3+) [2].In this work, a set of Eu doped oxygen rich silicon oxide (ORSO) thin films are fabricated using an integrated magnetron sputtering and electron cyclotron resonance plasma enhanced chemical vapor deposition (IMS-ECR-PECVD) system [3]. Following the deposition, the thin films are subjected to annealing using pure nitrogen (N2) and 95% of nitrogen and 5% of hydrogen (N2+H2) atmospheres and different temperatures ranging from 300 to 1350 °C. Performing the photoluminescence (PL) measurements shows that thin films annealed at elevated temperatures (above 1000 °C) exhibit more intense luminescence compared to the ones annealed at lower temperatures (below 900 °C). At annealing temperatures as low as 300 °C, PL intensity at 615 nm which is corresponding to 5D0 to 7F2 transition of trivalent Eu ion is observed. Furthermore, the effect of hydrogen passivation is investigated (as shown in Figure. 1.a) confirming the passivation resulting in an increase of PL intensity by one order of magnitude.Performing Rutherford backscattering spectroscopy (RBS) it is verified the Eu concentration of the thin films vary from 0.17 at. % to 6.36 at. %. It is observed that through IMS-ERC-PECVD system, the concentration of the RE, in this case Eu, can be controlled by manipulating the deposition parameters while the sputtering power shows the most considerable influence. Variable angle spectroscopy ellipsometry (VASE) is conducted to obtain the refractive index and thickness of the thin films. The incorporation of more hydrogen decreases the refractive index whereas the thickness is inversely proportional to hydrogen increase in the deposited film.X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) explain the PL behavior for samples annealed at higher temperatures. The formation of EuxSiyOz crystals approves the intense PL emission of samples annealed at elevated temperatures (above 1000 ºC) particularly at 1350 ºC while for the samples annealed at temperatures below 800 °C, the structure remains amorphous (shown in Figure 1.b).