Luminescence in Multilayers of SiGe Nanocrystals Embedded in SiO 2
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0958-L04-03
Luminescence in Multilayers of SiGe Nanocrystals Embedded in SiO2 Manuel Avella1, Ángel Carmelo Prieto1, Juan Jiménez1, Andrés Rodríguez2, Jesús Sangrador2, Tomás Rodríguez2, María Isabel Ortiz3, Carmen Ballesteros3, and Andreas Kling4,5 1 Física de la Materia Condensada, Univ. de Valladolid, E.T.S.I.I., Valladolid, 47011, Spain 2 Tecnología Electrónica, Universidad Politécnica de Madrid, E.T.S.I.T., Madrid, 28040, Spain 3 Física, Universidad Carlos III de Madrid, E.P.S., Leganés (Madrid), 28911, Spain 4 Instituto Tecnológico e Nuclear, Estrada Nacional 10, Sacavém, 2686-953, Portugal 5 Centro de Física Nuclear, Universidade de Lisboa, Lisbon, 1649-003, Portugal
ABSTRACT Luminescent multilayers of SiGe nanocrystals embedded in an oxide matrix have been fabricated by Low Pressure Chemical Vapour Deposition of a-SiGe and SiO2 in a single run followed by a Rapid Thermal Annealing treatment. The diameter of the nanoparticles, the oxide interlayer thickness and the annealing conditions have been investigated in order to get the maximum intensity of the luminescence. The structures with small nanoparticles (3-4.5 nm) separated by thick oxide barriers (≈ 35 nm) annealed at 900 ºC for 60 s yield the maximum intensity. These samples exhibit luminescence from 80 K to room temperature. An additional treatment at 450 ºC in forming gas further increases the intensity of this luminescence. INTRODUCTION Si or Ge nanocrystals embedded in SiO2 have been used in non-volatile memories and optoelectronic devices compatible with the CMOS technology [1-4]. SiGe nanocrystals with controlled composition and size and the appropriate areal density embedded in an oxide matrix have been obtained by Low Pressure Chemical Vapour Deposition (LPCVD) of amorphous discontinuous SiGe films followed by an annealing process [5]. Luminescence emission with a main band peaking at 400 nm was detected in this kind of structures, but its intensity was not optimized [6]. In this work, the diameter of the nanoparticles and the thickness of the SiO2 interdielectric layers (IDL), the post-growth annealing processes for nanoparticle crystallization and the effect of additional thermal treatments in forming gas have been investigated with the aim of the maximization of the luminescence intensity. EXPERIMENT Samples preparation Multilayer structures with five periods of amorphous SiGe nanoparticles/SiO2 and a top SiO2 capping layer were deposited to increase the areal density of nanoparticles. The samples deposition was carried out in a LPCVD reactor operating at a low constant temperature of 390 ºC
and a total pressure of 50 mTorr according to the procedures described elsewhere [5]. The SiGe nanoparticles, with a Ge fraction of x ≈ 0.4, were deposited using Si2H6 and GeH4 with a gas flow ratio of GeH4/Si2H6=0.82. The SiO2 layers were deposited using Si2H6 and O2 with a flow ratio of Si2H6/O2=0.2. Four types of samples were fabricated with two different diameters (d) of the nanoparticles and three different Table I Structural features of the four s
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