Visible Light Emission in Silicon-Interface Adsorbed Gas Superlattices
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Raphael Tsu, Jonder Morais* and Amanda Bowhill** University of North Carolina at Charlotte, Charlotte, NC 28223
*Present Address: UNICAMP, Physics Institute, Campinas, Brazil
"**Present Address: 155 A Round Hill Road, Northampton, MA 01060 Abstract
Having an indirect fundamental bandgap, unlike III-V or II-VI compound semiconductors, silicon has not played a role in optoelectronic applications such as injection lasers and light emitting diodes. In an attempt to introduce a sufficient quantum size effect, we present the experimental results on a new type of silicon based superlattices consisting of alternating layers of silicon and monolayers of adsorbed gases, Si/IAG multilayers (Si/Interface Adsorbed Gas), constructed by repeated interruptions of silicon deposition with adsorbed gases of oxygen and hydrogen. Fairly strong visible luminescence has been observed. Introduction In the past 30 years, the electronic industry has been overwhelmingly dominated by silicon. Having an indirect fundamental bandgap, silicon shows only weak phonon-assisted optical transition in the infrared. Without a strong optical transition, silicon has not played a role in optoelectronic technologies such as injection lasers and light emitting diodes. The observation of a strong photoluminescence in porous silicon, an electro-chemically etched porous material of single crystalline silicon, has been attributed to quantum size effects [1], both involving the widening of the energy bandgap due to quantum confinement [2], and the localization of the exciton [3]. Correlation of Raman and photoluminescence spectra of porous silicon further supported the quantum size effects and the role of microstructures in porous silicon [4]. However, surface effects should be more pronounced as particle size is reduced to the nanometer dimensions. Experiments with desorption of hydrogen and oxidation suggested a definite role of surface-related mechanism [5]. Microcrystals and nanocrystals form a class of materials that are neither single crystalline nor amorphous. Many of their properties are strongly influenced by surfaces, interfaces, and quantum size effects. As a result, nanocrystalline semiconductors display unique properties which may be exploited in future device applications. Recent attempts to produce nanometer-sized Si crystallites for optical applications are numerous [6]. Man-made superlattices fabricated of alternating layers of two materials were introduced primarily to broaden the available solids for electronic applications [7]. To further expand the available materials to include those with unacceptably high lattice mismatch, the concept and criteria for strain-layer superlattices were introduced [8, 9]. Recently, a new type of silicon based superlattice, utilizing a highly strained Si/SiOq, Si/CaF2, etc., epitaxial barrier system has been proposed [10]. Superlattices and related quantum wells have been developed into the mainstream of research and development in semiconductor physics and devices primarily with III-V and and II-VI compound
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