Origin of porous silicon photoluminescence: Evidence for a surface bound oxyhydride-like emitter
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, K1-83, Richland, Washington 99352 (United States)
Time-dependent excitation spectroscopy coupled with quantum chemical calculations is used to demonstrate that the photoluminescence (PL) resulting from the ultraviolet optical pumping of an etched porous silicon (PS) surface results from a silicon oxyhydride-like fluorophor bound to the PS surface. The time-dependent PL, in both aqueous (HF/H{sub 2}O and HF/CH{sub 3}OH/H{sub 2}O) and nonaqueous [MeCN/HF (anhydrous)] etching media, has been monitored both in situ, during the etching cycle and before the PS sample is removed from the etching solution, and ex situ, after removal of the PS sample from the etching solution. The early appearance in time of the PS luminescence is consistent with the formation of a surface bound emitter created on a time scale ({le}10s) much shorter than that needed for pore formation. Laser excitation spectra (PLE) over the wavelength range extending from 193 to 400 nm produce an almost identical time-dependent PL emission feature between 550 and 700 nm. Influenced strongly by the chemical composition of the etch solution, an intermediate {open_quotes}green{close_quotes} emitter can be excited with select laser pumping wavelengths and observed to transform to the final {open_quotes}orange-red{close_quotes} luminescent product. In conjunction with experiments whose focus has been to compare the time-dependent PL after ArF (193 nm) and N{sub 2} (337 nm) laser excitation (PLE), the data suggest the pumping of an excited-state manifold for a molecule-like species followed by rapid relaxation via nonradiative transitions down the manifold and the subsequent emission of radiation at much longer wavelength. Detailed quantum chemical modeling supports this interpretation and suggests a correlation to changes in the bonding associated with electronic transitions that involve silanone-like ground electronic singlet states and their low-lying triplet excitons. Especially important are those changes involving SiO related bonds. (Abstract Truncated)
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 547359
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 56, Issue 4; Other Information: PBD: Jul 1997
- Country of Publication:
- United States
- Language:
- English
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