Amorphous sub-nanometre Tb-doped SiOxNy/SiO2 superlattices for optoelectronics. (6th February 2015)

• Record Type: Journal Article
• Authors: Ramírez, Joan Manel; Wojcik, Jacek; Berencén, Yonder; Ruiz-Caridad, Alícia; Estradé, Sònia; Peiró, Francesca; Mascher, Peter; Garrido, Blas
• Is Part Of: Nanotechnology. Volume 26:Number 8(2015)
• Publication Date: 2015-02-06
• Subjects: silicon-based light sources -- amorphous superlattice -- charge transport -- Tb luminescence; Nanotechnology -- Periodicals; Nanotechnology -- Periodicals; Nanotechnology; Publications périodiques; Nanotechnologies; Periodicals; 620.5
• DOI: 10.1088/0957-4484/26/8/085203
• Languages: English
• ISSNs: 0957-4484

Abstract

Abstract: Amorphous sub-nanometre Tb-doped SiO x N y /SiO2 superlattices were fabricated by means of alternating deposition of 0.7 nm thick Tb-doped SiO x N y layers and of 0.9 nm thick SiO2 barrier layers in an electron-cyclotron-resonance plasma enhanced chemical vapour deposition system with in situ Tb-doping capability. High resolution transmission electron microscopy images showed a well-preserved superlattice morphology after annealing at a high temperature of 1000 °C. In addition, transparent indium tin oxide (ITO) electrodes were deposited by electron beam evaporation using a shadow mask approach to allow for the optoelectronic characterization of superlattices. Tb 3+ luminescent spectral features were obtained using three different excitation sources: UV laser excitation (photoluminescence (PL)), under a bias voltage (electroluminescence (EL)) and under a highly energetic electron beam (cathodoluminescence (CL)). All techniques displayed Tb 3+ inner transitions belonging to 5 D4 levels except for the CL spectrum, in which 5 D3 transition levels were also observed. Two competing mechanisms were proposed to explain the spectral differences observed between PL (or EL) and CL excitation: the population rate of the 5 D3 state and the non-radiative relaxation rate of the 5 D3 – 5 D4 transition due to a resonant OH-mode. Moreover, the large number of interfaces (trapping sites) that electrons have to get through was identified as the main reason for observing a bulk-limited charge transport mechanism governed by Poole–Frenkel conduction in the J – V characteristic. Finally, a linear EL– J dependence was measured, with independent spectral shape and an EL onset voltage as low as 6.7 V. These amorphous sub-nanometre superlattices are meant to provide low-cost solutions in different areas including sensing, photovoltaics or photonics.