Nano-Porous Silicon for Sensors and Solar Cells

Nano-Porous Silicon for Sensors and Solar Cells E. Manea*, C. Podaru*, A. Popescu*, E. Budianu*, M.Purica*, F. Babarada**, C. Parvulescu** *National Institute for Research and Development in Microtechnologies, Bucharest, 72996, Romania ** Faculty of Electronic and Telecommunication, "Politechnica" University of Bucharest, Romania Abstract. We report an experimental study of porous silicon layers for sensors and silicon solar cells applications . The layers of porous silicon were formed by electrochemical etching of the crystalline silicon wafers, using a mixture of hydrofluoric acid and ethanol as electrolyte for PV applications and HF in DMF for sensor devices. The pores size varies from a few nm to a few microns depending on the conditions of formation and the characteristics of the silicon wafer. Keywords: porous silicon, anodic oxidation films, solar concentrators PACS: 42.79Ek, 84.60.Jd, 82.45.Cc, 78.55.Mb

INTRODUCTION Porous silicon (PS) is a material that has been applied to different optoelectronic devices including sensors. Applications of PS have emerged in many technical fields, such as sensors as sensitive layer and in solar cells, essentially, as antireflection coating, due to low reflectance values and also due to potential passivation properties of the PS layers.

EXPERIMENTAL

FIGURE 1. SEM image of porous silicon layer

PS samples used in PV applications were prepared by electrochemical etching using as starting material crystalline p-Si wafers (100), 0.02 £2cm resistivity, phosphorus doped and HF:C2H5OH:H20 as electrolyte. The current density range, 5 to 18 mA/cm2 , anodisation time, 600 s, illumination, a 500 W halogen lamp, T=300K. To obtain sensitive layers it was used an electrolyte such as: 4% HF in DMF.

It can see that the reflectance of the porous layer is lower than reference sample (n+/p Si).

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RESULTS

FIGURE 2. Spectral dependence of reflectance for porous silicon samples (C1-C4) and reference (n+/p Si).

Gravimetric measurements were used to determine the average density of the analyzed porous layers (PSL). Thickness dependence of PSL and pores geometry on the parameters of etching process was established from the SEM measurements. SEM images of the porosified layers showed the homogeneity of pores on the silicon surface and, their sizes of around 8 nm, Fig. 1. The reflectance spectra of the PSL were recorded in the wavelength range from 350 nm to 900 nm using a double beam spectrophotometer, Fig. 2.

CONCLUSION A low-cost electrochemical etching was used to form the PSL for applications in the sensors field and in the PV, in order to reduce the light power losses by surface reflection. For this purpose, PSL with pores dimensions in the range of an 8 nm to 2 urn depending on the conditions of formation and the characteristics of the silicon wafer have been obtained.

CP899, Sixth International Conference of the Balkan Physical Union, edited by S. A. Cetin and I. Hikmet © 2007 American Institute of Physics 978-0-7354-0404-5/07/$23.00 759 Downloaded 03 May 2007 to 86.121.106.64. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp