Effect of Microcavity Structures on the Photoluminescence of Silicon Nanocrystals
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Effect of Microcavity Structures on the Photoluminescence of Silicon Nanocrystals Marc G. Spooner, Timothy M. Walsh and Robert G. Elliman Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia. 2 34
ABSTRACT Optical microcavity structures containing Si nanocrystals are fabricated by plasma enhanced chemical vapour deposition (PECVD) of SiO2, Si3N4 and SiOx layers. The nanocrystals are formed within Si-rich oxide layers (SiOx) by precipitation and growth, and the microcavity structures defined by two parallel distributed Bragg mirrors (DBM) made from either alternate SiO2/Si3N4 layers or alternate SiO2/SiOx layers. In the latter case, Si nanocrystal layers form part of the DBM structure thereby providing a distributed emission source. The optical emission from these and related structures are examined and compared with that from isolated nanocrystal layers.
INTRODUCTION Silicon’s pre-eminence in high-speed digital electronics does not generally extend to optoelectronics where the demand is for devices that can generate, guide, detect and process optical signals. However, the advantage of being able to integrate electronic and photonic functionality in a single circuit has stimulated a search for approaches that overcome silicon’s intrinsic limitations. These include doping with active impurities, such as rare-earth ions[1,2] (e.g. Er), the use of new phases such as silicides (e.g. Fe2Si3)[3], the direct modification of the band-structure of silicon by alloying[4] (e.g. alloys of Si with Ge, Sn and/or C) and the use of defect luminescence[5]. Such approaches remain active areas of research and prototypic devices have been demonstrated in some cases. However, the discovery in 1990 that porous[6] and nanocrystalline[7] silicon exhibited strong visible luminescence at room temperature provided an exciting alternative that has also received considerable attention[8]. The optical emission from porous and nanocrystalline Si has a broad spectral range as a consequence of the inhomogeneous broadening caused by the distribution of crystal sizes[8]. Reducing the spectral width and increasing the emission intensity is highly desirable for device applications and several approaches have been examined in this context. These include the use of nanocrystal-impurity interactions, in which nanocrystals act as a sensitizer for impurity emission[9-12], and the use of optical microcavities, in which the optical emission is controlled by an optical structure[13-15]. The former approach enables broad band excitation of the impurity emission and can increase the excitation cross section by up to 4 orders of magnitude. The latter approach, on the other hand, has the advantage of tunability (over the wavelength range of the nanocrystal emission) as well as providing narrow-band emission and enhanced emission intensity. In the present study, plasma-enhanced chemical vapour deposition (PECVD) of SiO2, SiOx and Si3N4 layers is u
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