STRUCTURE AND PHOTOLUMINESCENCE PROPERTIES OF Porous Silicon
PREPARED IN IODINE CONTAINED ELECTROLYTES:
V.A. Karavanski1*, I.V. Kavetskaya2, N.N.Melnik3 T.N. Zavaritskaya3
1Natural SciencesCenter of General Physics Institute,
RussianAcademy of Sciences, 38/L2 Vavilov str., Moscow, 119991 Russia
2Voronez State Universit, 1 University square, Voronezh, 394000, Russia
3Lebedev Physical Institute, Russian Academy of Sciences, Leninski .pr. 53, Moscow, 119991 Russia
* e-mail:
Introduction
Porous silicon (PS) has about 50 year history include more than 10 years after discovering of visible intense photoluminescence (PL) phenomena. Now is doubtless that the nanocrystalline nature of porous silicon is responds for its PL properties. Intensive investigation of silicon nanostructures resulted in preparing light amplifying silicon nanocrystalline structures and the next step is creation of silicon-based lasers. Nevertheless porous silicon remains still intriguing object of investigation. First of all it is concerned of the understanding and description of the formation mechanisms; include the description of the morphology features and surface properties for the cases of anodization processes in the dark and with external light illumination or with modified electrolytes. Another question is the role of nanocrystal interactions in its optical and luminescence properties. An important problem is still remains the stability of the porous silicon. One of the task is to prepare efficient photoluminescent PS structures on high doped silicon. An external light illumination improves PL efficiency of PS, but produces the inhomogeneous layers.
Main electrolytes for porous silicon preparation are HF-based solutions or other solutions which supply fluorine ions in acidic environment. An attention was paid to the investigations with processing of PS by another halogen ions such Cl, Br, I, or using electrolytes with their adding. Improved stability with formation of very thin perfect SiO2 passivation was obtained by anodization of silicon with adding of HCl in HF-based electrolyte or by post-treatment of PS in HCl solutions. Less impressive results were observed by processing PS in solutions of HBr and HI acids or in iodine solutions. On the other hand it is well known, that iodine solutions are very effective for suppressing of surface recombination in technique of carrier recombination lifetime measurements. Thereby, one can expect that iodine will be effective for achieving of enhanced stability of PS under some determined condition.
Luminescent porous silicon samples were prepared by anodization in iodine contained HF-based electrolytes on a heavy doped (0.01 Ohm∙cm) n-type silicon substrates. Comparative studies of the photoluminesce properties of these samples with similar PS obtained in electrolytes without iodine and usual PS prepared on a moderately doped p-type silicon or on a heavy doped n-type silicon with light illumination are presented. Structural properties study by atomic force microscopy (AFM) of PS samples obtained without and with using of iodine in the electrolyte are presented.