........ published in NEWSLETTER # 49
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........ published in NEWSLETTER # 49
OPTICAL PROPERTIES OF LOW DIMENSIONAL SILICON STRUCTURES
by D.C. Bensahel, Telecom (France), L.T. Canham, DRA (U.K.) and S. Ossicini, University, Modena (Italy)
This book reviews the state_of_the_art of the intensive worldwide research activity devoted to the optical properties of low dimensional silicon structures and in particular of porous_silicon. This follows the recent discovery of efficient visible photoluminescence (PL) from highly porous silicon.
The first part of the book (NATO ASI SERIES E244) is devoted to the material aspects with special emphasis on porous silicon: in particular, a new electrochemical method for the determination of the surface area of high porosity samples is presented, as is the fabrication procedure of thin wires using advanced lithography (smaller than 100 nm) and etching. This latter technique, although it provides only a weak PL, can nevertheless significantly further our understanding of the optoelectronic properties of highly porous_Si.
The second part of the book is devoted to the characterisation techniques and luminescent properties of porous_Si: Transmission Electron Microscopy has clearly established the crystallinity of highly porous_Si; Tunneling Microscopy as well as the EPR technique are under development and will undoubtedly yield valuable information on luminescent layer morphology and the role of defects on the internal surface. Other sophisticated techniques such as ellipsometry, continue to provide new insights. Luminescence studies have been numerous and have given rise to several models. The majority of the participants agree (i) on the quantum confinement effect and (ii) the good passivation of the surface crystallites (by H_bonds in `fresh' porous_ Si or thermal SiO2 after high temperature oxidation). The results obtained by ab_initio calculations so far are consistent with the confinement hypothesis and explain qualitatively the dependence of the PL decay time on wavelength.
Both the efficient and wavelength tunable electroluminescence (EL) are demonstrated using liquid contacts and a cathodic injection system. Localised cathododluminescence in a Scanning Electron Microscope and a Scanning Tunneling Microscope are presented.
Finally, this book will be of interest to anyone working on the origin of the visible luminescence of highly porous_Si. This novel nanostructure is extending our knowledge into a new area of solid state physics.
Reference books: E136, E160, E193, E244