Quantum Dots and Quantum Wires Contribution on Photoluminescent Properties of Nanostructured Oxidized Silicon
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Quantum Dots and Quantum Wires Contribution on Photoluminescent Properties of Nanostructured Oxidized Silicon C. Vargas,1,2 T. Ramírez-Cortés,1,2 K. Cordero-Solano,2 and A. Ramírez-Porras1,2 1 Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Universidad de Costa Rica, San Pedro 11501, San José, Costa Rica 2 Escuela de Física, Universidad de Costa Rica, San Pedro 11501, San José, Costa Rica ABSTRACT Stability of functional devices such as light-emitting devices and chemical or biological sensors is an important issue nowadays. Nanostructured silicon made using top-down methodologies is being employed as a material to develop such systems, but surface stability to external ambient conditions is still an open question. One of those important conditions is oxidation. Although there exist models accounting for the role of oxide layers on semiconductor systems, experimental data is still required to provide further useful information. In this paper, we perform oxidation processes to light-emitting nanostructured silicon and study the contribution of quantum dots and quantum wires to photoluminescence as surface oxidation evolves. Cross-correlations with infrared spectroscopy are also included. INTRODUCTION Nanostructured silicon exhibits photoluminescent characteristics that have been extensively studied for more than a couple of decades.1 Since then, articles dealing with the production of silicon nanocrystals based light-emitting diodes,2,3 chemical and biological sensors,4 and other applications were reported. It is widely accepted that nanostructured silicon is made of a collection of quantum dots (QD) and quantum wires (QD). The role of these quantum species on photoluminescence (PL) has also been studied earlier.5–7 In these, the oxidation degree of the surface impacts the PL characteristics. In the present paper, we concentrate on the contribution of QD and QW when the nanostructured surfaces are progressively oxidized. QD and QW contributions on PL can be calculated from an already published model.6 In this model, the probability distributions for these quantum species are calculated in terms of mean diameters and their corresponding standard deviations. These are the interesting parameters extracted from the PL spectra that will be reported here. EXPERIMENTAL SETUP Photoluminescent samples were obtained by a usual electrochemical etching method.7 Boron-doped crystalline silicon (CS) pieces of 1×1 cm2, (100) crystal orientation and 20-50 Ω cm resistivity, were employed. The etching procedure was performed in a Teflon cell where one sample was located on the bottom part facing upwards and in contact with the solution. The exposed area was a disk of 0.13 cm2. A platinum foil immersed in the solution was the cathode, and a 100 nm depth back aluminum contact deposited previously by vacuum evaporation process
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