Controlling the Er content of porous silicon using the doping current intensity
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NANO EXPRESS
Open Access
Controlling the Er content of porous silicon using the doping current intensity Guido Mula1*, Lucy Loddo1, Elisa Pinna1, Maria V Tiddia1, Michele Mascia2, Simonetta Palmas2, Roberta Ruffilli3 and Andrea Falqui4
Abstract The results of an investigation on the Er doping of porous silicon are presented. Electrochemical impedance spectroscopy, optical reflectivity, and spatially resolved energy dispersive spectroscopy (EDS) coupled to scanning electron microscopy measurements were used to investigate on the transient during the first stages of constant current Er doping. Depending on the applied current intensity, the voltage transient displays two very different behaviors, signature of two different chemical processes. The measurements show that, for equal transferred charge and identical porous silicon (PSi) layers, the applied current intensity also influences the final Er content. An interpretative model is proposed in order to describe the two distinct chemical processes. The results can be useful for a better control over the doping process. Keywords: Porous Silicon; Er doping; Electrochemical impedance spectroscopy; Reflectivity; Scanning electron microscopy Pacs: 81.05.Rm; 82.45.Rr
Background The rare earth doping of Si as a means to obtain efficient light emission 1.5 μm has attracted a lot of interest [1-7] since, given its indirect bandgap, Si photoluminescence can be obtained only through strong quantum confinement [8]. Porous silicon (PSi) studies already reported interesting Er-related photoluminescence [2,9-11] or electroluminescence [12]. Unfortunately, this research activity did not lead, till now, to market-valuable devices, basically because almost no research has been devoted to the understanding of the doping process itself. Most studies, even very recent ones [11], use only optical properties as a means to optimize the Er doping process on bulk Si [10] or PSi [3,9]. However, given the large internal surface of the material, the electrochemical doping of PSi is a quite complex process that we are just beginning to understand: all we have are just a few studies on the cyclic voltammetry of the Er deposition process [13], on the effect of doping duration [7], and on the
* Correspondence: [email protected] 1 Dipartimento di Fisica, Cittadella Universitaria di Monserrato, Università degli Studi di Cagliari, S.P. 8 km 0.7, Monserrato, Cagliari 09042, Italy Full list of author information is available at the end of the article
evolution of the doping process as a function of several parameters [14,15]. The luminescence in itself being not an issue, we focused our study on the control of the electrochemical doping process of PSi. We will show that gaining detailed information about the early stages of the process is instrumental for understanding the final results of the doping process and the key for its optimization. In our study, significant information in the understanding of these early stages is obtained by electrochemical impedance spectroscopy (EIS). This is a
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