JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 10, No. 10, October 2008, p. 2653 - 2656 Spectroscopic investigation of porous silicon prepared by laser-induced etching KHALID M. OMAR * , N. K. ALI, Z. HASSAN, M. R. HASHIM, H. ABU HASSAN School of Physics, Universiti Sains Malaysia, 11800-Penang, Malaysia Porous silicon was prepared by using an argon-ion laser in a laser-induced etching process with different etching time. Scanning electron microscopy was used to monitor changes in surface morphology produced during the etching process. Porous silicon samples were subjected to spectroscopic investigations. The first-order Raman line asymmetry was found to decrease with increase of the etching time, while the peak position downshifted for a given power density. The photoluminescence spectra (PL) exhibit a blue shift in peak position with etching time. Both Raman and PL data were explained using appropriate quantum confinement models involving three-dimensional confinement and Gaussian size distributions of nanocrystallites constituting porous silicon samples. There is reasonable agreement between the results obtained from Raman and PL spectroscopic investigations of the PS samples. (Received May 14, 2008; accepted August 14, 2008) Keywords: Porous silicon, Laser- induced etching, Raman spectra, Photoluminescence 1. Introduction Porous silicon (PS) layers have been intensely studied since the discovery of an efficient visible luminescence in 1990 [1]. Light emitting silicon nanostructures have been produced by using a wide range of different techniques [2, 3]. Electrochemical anodization with direct current (dc) is the most commonly used technique for the formation of porous semiconductors [4-6]. Both the thickness and the crystallite size can be adjusted with this technique, thus enabling us to control the optical and electrical behavior of PS layers [7]. However, isolating the metal contacts from the solution has been the major drawback of this technique. Stain-etching technique (electroless) can also be used to form porous layers in Si [8]. Major difference between the two techniques is the formation rate and the thickness limitation in the latter one. Recently, a new method, termed metal-assisted chemical etching, has been developed, which is relatively simple compared to the anodization method. It needs no electrodes on the back surface of Si wafers and enables formation of uniform porous silicon layers [9,10]. Laser induced etching is another versatile technique that allows the formation of nanostructures which are determined by the photon energy, power density of laser beam illumination on the sample surface and the routine parameters like types of etchants, composition of electrolyte, temperature etc. Reports are available in the literature about this etching technique employed for Si [11, 12] and GaAs [13] nanostructures fabrication. In this work, we have fabricated PS nanostructure by laser- induced etching using an argon-ion laser (λ= 488 nm), which is probably the simplest technique to produce nanocrystallites and sizes can be controlled by changing the etching time. The information regarding the surface morphology can be obtained by using scanning electron microscopy (SEM). Photoluminescence and Raman spectroscopic studies are also reported to examine the formation of nanocrystallites in the PS after laser etching. The size and size distributions estimated by the analysis of the PL and Raman data using the existing quantum confinement models agree reasonably well. 2. Experimental Fig. 1 shows a schematic diagram of the experimental set-up for the laser induced etching. A commercially available n-type Si wafer with resistivity of 1 Ohm-cm was immersed in hydrofluoric acid with 49% concentration placed in a Teflon container and was supported on two Teflon plates. Laser etching was done by using an argon–ion laser with photon energy of 2.54 eV (λ= 488 nm). The beam was focused to a circular spot of 1.5mm diameter with a power density of 12 W cm −2 . The samples were etched in this way for 30, 60 and 90 min of exposure with the laser and subsequently the samples were rinsed with ethanol and dried with filtered N 2 . The surface morphology of the etched PS was studied by SEM.