Fast and slow visible luminescence bands of oxidized porous Si

Abstract

The visible luminescence of porous Si is known to contain at least two spectrally distinct emission bands with widely different response times. The orange-red luminescence component (1.5–1.9 eV) decays in times being of the order of 10 μs at room temperature. The blue-green band (2.3–2.6 eV) is very much faster with response time in the 10-ns range. It is shown that with increasing degree of oxidation the fraction of the fast luminescence intensity rises from ∼1% of the total in the as-prepared porous Si to become the dominant spectral component in strongly oxidized material. For the rapid-thermal-oxidized material excited with 337-nm radiation, the intensity of the fast luminescence is comparable to that in the as-prepared state.

Luminescence Bands and their Proposed Origins In Highly Porous Silicon

“…They attributed it t o direct T-T transitions in silicon nanocrystallites. 'Strong' blue emission was subsequently observed from porous Si oxidised a t elevated temperatures [27] and after photo-assisted anodisation a t room temperature [28]. This prompted increased recent interest in this band and blue emission has now been observed from oxidised Si structures prepared by a variety of techniques [27 to 321.…”

“…'Strong' blue emission was subsequently observed from porous Si oxidised a t elevated temperatures [27] and after photo-assisted anodisation a t room temperature [28]. This prompted increased recent interest in this band and blue emission has now been observed from oxidised Si structures prepared by a variety of techniques [27 to 321. However, it is important to note that blue emission from defective silica alone is also well documented, for a recent example, see [33].…”

Unusual Photoluminescence Decay of Porous Silicon Prepared by Rapid Thermal Oxidation and Quenching in Liquid Nitrogen

“…Furthermore, the rapid thermal oxidation (RTO) treatment of as-anodized PS brings about a significant blue shit of the original PL peak position from 650-800 nm (red) to 430-550 nm (blue-yellow). 9,10) The lifetime of the red photoluminescence at room temperature is in the microsecond range ("slow luminescence"), 11) whereas that of the blue-yellow luminescence is in the nanosecond range ("fast luminescence"). It appears from these facts that modifications of PS by physical as well as chemical means may be the key to accession of new luminescence properties.…”

Hybrid Optoelectronic and Photovoltaic Materials based on Silicon Nanocrystals and Conjugated Polymers

“…Figure 2 represents the shift of PL maxima as a function of temperature for Si-ncs prepared by electrochemical etching and laser ablation in water. It is supposed that the red shift is mainly attributed to the decrease in the band gap energy with temperature, which is typical for semiconductor materials due to the many possible electronic states in Si-ncs (Kovalev, et 1994;Zhuravlev et al, 1998;Garcia et al, 2003). At 4 K, the contribution from quantum confinement is distinguished quite well and one could evaluate real Si-ncs size.…”