Boron engineered dislocation loops for efficient room temperature silicon light emitting diodes M.A. Lourenc ¸o a, * , M. Milosavljevic ´ a,1 , G. Shao b , R.M. Gwilliam a , K.P. Homewood a a Advanced Technology Institute, School of Electronics and Physical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK b BCAST, Brunel University, Uxbridge UB8 3PH, UK Available online 29 September 2005 Abstract The dislocation engineered approach makes use of the controlled introduction of dislocation loops into silicon substrates by conventional ion implantation and thermal processing. The dislocation loops introduce a local strain field, which modifies the band structure and provides spatial confinement of the charge carriers, thus allowing strong intrinsic silicon band-edge luminescence to be observed at room temperature. Efficient silicon-based dislocation engineered light emitting diodes were fabricated under different process conditions to study the influence of the dislocation loops formation on the luminescence properties. Electroluminescence and transmission electron microscopy techniques were used to characterise the devices and the results showed that (i) the size and density of the loops vary with boron implant energy and post-implant anneal conditions and (ii) the luminescence response from such devices can be directly related to the size and density of the dislocation loops. D 2005 Elsevier B.V. All rights reserved. Keywords: Silicon; Electroluminescence; Dislocation engineered; Light emitting devices 1. Introduction Although silicon is the material of choice for most microelectronic applications, light emission from Si is ineffi- cient due to its indirect band gap. Despite this intrinsic problem, many approaches have been tried to obtain efficient light emission in silicon based devices. Porous silicon [1], silicon/silicon dioxide superlattices [2], silicon nanoprecipitates in silicon dioxide [3], erbium in silicon [4], silicon/germanium [5] and iron disilicide [6] are potential routes to realize light emission. However, a common problem found in these devices is the strong thermal quenching leading to very poor performance at room temperature. Ng et al. [7] proposed a new method for device fabrication, the dislocation engineered approach, in order to solve the general thermal quenching problem of luminescence frequently found in semiconductors. In this approach, the thermal quenching giving poor room temperature luminescence can be minimised by the controlled introduction of dislocation loops. This introduces a strain field outside the loop that increases the silicon band gap by up to 0.75 eV and enables spatial confinement of the injected carriers, so diffusion of injected carriers to point defects and the surface, where efficient non-radiative recombination occurs, is suppressed or eliminated. This method has been applied, for example, to fabricate efficient h-FeSi 2 LEDs [8], and the results show that the thermal quenching has been reduced to only one order of magnitude of that of the low temperature emission, making these much more efficient than conventional devices, where temperature quenching of four orders of magnitude or higher has been recently reported [9]. The role of boron ion energy in engineering of dislocation loops for silicon light emitting diodes (LEDs) has been previously studied [10]. Boron ions from 10–80 keV were implanted in (100) Si, to a constant fluence of 1 Â 10 15 ions/ cm 2 . After irradiation the samples were annealed at 950 -C for 20 min by rapid thermal annealing and were analysed by transmission electron microscopy and Rutherford backscatter- ing spectroscopy. It was found that the ion implantation and thermal processing induce interstitial perfect and faulted dislocation loops. The loops are located around the projected 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.09.036 * Corresponding author. Tel.: +44 1483 682740; fax: +44 1483 689404. E-mail address: M.Lourenco@surrey.ac.uk (M.A. Lourenc ¸o). 1 On leave from: VINC ˇ A Institute of Nuclear Sciences, Belgrade, Serbia and Montenegro. Thin Solid Films 504 (2006) 36 – 40 www.elsevier.com/locate/tsf