PARTIAL OXIDATION OF POROUS SILICON BY THERMAL-PROCESS - STUDY OF STRUCTURE AND ELECTRONIC DEFECTS

We present a preliminary study on thermal oxidation of porous silicon with the aim to form Si single crystal nanostructures, with controlled sizes. Porous silicon layers, prepared by electrochemical etching of (100) p(+) material, were oxidized at high temperature (1000 degrees C), low oxygen pressure (12 mbar) during varying time (0-10 min) in a set-up allowing treatments in a controlled atmosphere. The composition of the layers and their oxygen content have been determined using nuclear reaction analysis and Rutherford backscattering spectrometry. From oxygen measurements, the lateral size of the Si wires has been estimated as a function of the oxidation time. According to our estimations, thermal oxidation during 10 min should lead to silicon wires of 5 nm lateral size about. Photoluminescence and electron paramagnetic resonance measurements have been performed on these samples. The PL integrated signal increases as a function of the oxidation time but is weaker than the one observed in p(+) porous layer of high porosity obtained directly by electrochemical etching. This was correlated to a decrease of the (111) P-b defects density which, however, remains high. The weak PL signal could also be due to the relatively high size of the Si nanostructures.