Anomalous behaviour of stain etched porous silicon photoluminescence
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A17.16.1
Anomalous behaviour of stain etched porous silicon photoluminescence Ricardo Guerrero-Lemus, Fathi A. Ben-Hander1, Cecilio Hernández-Rodríguez and José M. Martínez-Duart1 Dept. Física Básica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, 38204 La Laguna, S/C Tenerife, SPAIN. 1 Dept. Física Aplicada C-XII, Universidad Autónoma de Madrid, 28049 Madrid, SPAIN.
ABSTRACT
In this work we present a comparative study of porous silicon (PS) photoluminescence for samples stain etched and electrochemically etched. The etching parameters for both types of samples have been adjusted to obtain similar porous structures. The photoluminescence spectra have been obtained varying the excitation energy between 2.48 and 3.54 eV. The variation of the excitation energy produces differences in the evolution of the emission energy maximum between both types of PS. This behaviour is attributable to the differences in oxidation level in the porous structure. Also it has been established a higher concentration of luminescent centers for stain etched PS.
INTRODUCTION
Porous silicon (PS) has been studied from the middle of the 50's [1]. However, the discovery at the beginning of the 90's that PS shows notorious photoluminescent [2] and electroluminescent [3] properties has sparked hopes that fabrication of optoelectronic circuits integrated on a single substrate may become feasible in the near future. Electrochemically etched PS (EEPS) has been the procedure mainly used to produce Si luminescent nanostructures due to its low cost and because it allows a suitable control of the formation process [2]. Nevertheless, the electrochemical process presents the difficulty of realizing good electrical contacts to its surface. At the beginning of the 90's the formation of stain etched PS (SEPS) showing luminescence was achieved by the chemical attack in HF/HNO3 solutions [4-5]. Initially, the stain etching technique was not very successful, due to difficulties in the control of the process [6]. However, later studies demonstrated that in low concentration HNO3 solutions, the SEPS samples showed excellent and reproducible luminescent properties [7]. Also, the achievement of reflectance values below 4 % (300 - 1100 nm) confirmed the potential advantages of SEPS as antireflection coating for silicon-based solar cells [7]. Due to its photoluminescent properties [4], SEPS can also convert high energy solar photons into photons of lower energy, increasing the photoconversion efficiency of the solar cells [8]. Nevertheless, few works have been published on the photoluminescent properties of SEPS [9-10]. In this work it is shown a comparative study of the SEPS and EEPS luminescence properties. Previously, the etching parameters have been adjusted to assure that the porous layers
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A17.16.2
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