Formation of Intensive Photoluminescence in Porous Silicon
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V.A. MAKARA, M.S. BOLTOVETS, O.V. VAKULENKO, 0.1. DATSENKO, O.V. RUDENKO Taras Shevchenko Kiev National University, Department of Physics, Volodymyrska St., 64, Kyjiv, 252033, Ukraine ABSTRACT
Photoluminescence (PL) spectra of porous silicon (PS) samples are studied. Effect of mechanical stresses in substrate on PL intensity is shown. The quantum yield (QY) of PS luminescence is estimated by comparing PL spectra of PS and rhodamine 6G. INTRODUCTION
Significant scientific interest to porous silicon is attracted above all by the detection of its bright photoluminescence in the visible spectral region [1]. The prospects of PS practical implementation as an electronic material will be appreciably defined by technological possibilities of formation of PS structures with a high quantum yield. It is found that saturation of PS surface by hydrogen [2], oxigen [3] and sulphur [4] adds luminescence intensity, which is ascribed to elimination of one of nonradiative recombination channels due to existence of broken chemical bonds at the surface of porous layer crystallites [3]. However, in the cited papers there are no estimates of the PL QY attained on the studied samples and so the questions whether charge carrier recombination at the broken bonds is a main non-radiative recombination channel and whether any reserves for considerable increase in PS PL
QY exist, still remain open.
To answer somehow these questions, we used familiar to experts possibilities for optimization of PS formation conditions. Particular attention was given to the effect of mechanical stresses in the substrate on the efficiency of PS film formation in anode etching silicon wafer in hydrofluoric acid [5]. EXPERIMENT
PS layers were formed on substrates of KDB-10-type silicon (boron-doped hole conductivity single-crystalline silicon with resistivity of 10 Q.cm) and KEM-0.001 silicon (As-doped electron conductivity silicon, 0.001 Qi.cm) with [111] orientation by electrolytic anodizind in water (or water with acetone) solutions of HF acid with concentration between 0:1 and 2:3 with current density from 10 to 100 mA/cm 2 during 1-4 minutes. The films ranged in thickness from 2 to 10 pim. Before anode etching, at back side of some samples was graved a grid of scratches by a Vickers diamond pyramid with the help of a PMT-3-type device. The load on the indenter was from 10 to 200 g. The PL was excited by an ILGI-503-type nitrogen laser (337 nm). To estimate the QY of PS luminescence, PL spectra of ethanole-based solutions of rhodamine 6G 193 Mat. Res. Soc. Symp. Proc. Vol. 405 01996 Materials Research Society
were measured as well. The experiment geometry was the same in both cases. The laser radiation failed on the PS sample (or the cuvette with rhodamine solution) at an angle of 100. The concentration of rhodamine 6G in the solution was matched to provide a maximum light signal. RESULTS
Photoluminescence spectra of porous silicon The PL spectra consisted of a single 1.9 eV band with a half-width of 0.4 eV, it having slight structure and being near-Gau
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