Abstract
In systems in atomic and nano scales such as clusters or agglomerates constituted of particles from a few to less than one hundred of atoms, quantum confinement effects are very important. Their optical and electronic properties are often dependent on the size of the systems and the way in which the atoms in these clusters are bonded. Generally, these nano-structures display optical and electronic properties significantly different of those found in corresponding bulk materials. Silicon agglomerates found in Silicon Rich Oxide (SRO) films have optical properties, which have reported as depended directly on nano-crystal size. Furthermore, the room temperature photoluminescence (PL) of Silicon Rich Oxides (SRO) has repeatedly generated a huge interest due to their possible applications in optoelectronic devices. However, a plausible emission mechanism has not yet widespread acceptance of the scientific community. In this research, we employed the Density Functional Theory with a functional B3LYP and a basis set 6 - 31G* to calculate the optical and electronic properties of small (six to ten silicon atoms) and medium size clusters of silicon (constituted of eleven to fourteen silicon atoms). With the theoretical calculation of the structural and optical properties of silicon clusters, it is possible to evaluate the contribution of silicon agglomerates in the luminescent emission mechanism experimentally found in thin SRO films.
Highlights
Canham [1] reported visible light emission from porous silicon at room temperature in 1990 and since silicon associated materials have received a huge interest and have been studied intensively for their relevance to the development of nano-electronics
Silicon nano-crystals (Si-nCs) can emit and absorb light at energies which can be controlled by their sizes
Silicon nano-crystals (Si-nCs) and silicon agglomerates have been characterized in Silicon Rich Oxide (SRO) films employing Transmis-Open Access
Summary
Canham [1] reported visible light emission from porous silicon at room temperature in 1990 and since silicon associated materials have received a huge interest and have been studied intensively for their relevance to the development of nano-electronics. Crystalline silicon has an indirect band gap, which means, every optical transition must be accompanied by the creation or annihilation of a phonon Another disadvantage is due to the low band gap value Eg,c-Si = 1.12 eV (at Room Temperature) corresponding to a wavelength λg,c-Si = 1107 nm: the radiation emitted by a light emitting diode (LED) built of c-Si corresponds with infrared and is non-visible by the human eye. It is possible that silicon small size agglomerates (Sin, n < 20) were presented in these particular films (R0 = 30) which would hardly be detected due to atomic instead nano scale. The equilibrium energy calculated of several propose d Si clusters at ground state and the six first excitation states calculated result very useful to evaluate the possible contribution to the PL from different silicon structures present in SRO films
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