Chemical Treatment Effects on Si(111) Surfaces in Aqueous NaF Solution

2006

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Stable ultraviolet ͑UV͒ photoluminescence ͑PL͒ has been observed at room temperature in porous silicon ͑PSi͒ fabricated by photoetching in aqueous alkali fluoride solutions. The aqueous solutions used are 1 M NaF and 1 M KF. They give an alkaline reaction caused by partial hydrolysis. The PL peaks at ϳ3.3 eV have a full width at half maximum of ϳ0.1 eV, which is much smaller than those reported previously ͑ജ0.5 eV͒. Spectral analyses suggest that both quantum confinement and surface passivation effects enable the observation of UV emission in NaF-and KF-prepared PSi samples.

Section: Discussionmentioning

confidence: 59%

“…12 The illumination of a He-Ne laser produces free electron ͑e − ͒-hole ͑h + ͒ pairs in the silicon substrate, as shown in Fig. 3͑b͒.…”

Section: Fig 2 Large-scale Afm Images Ofmentioning

confidence: 99%

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Ultraviolet emission from porous silicon photosynthesized in aqueous alkali fluoride solutions

Uchida

Tomioka

2006

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“…The native oxide thickness d ox can be estimated from the measured XPS intensity of oxide, I ox , and of GaP, I GaP , by the following expression 29 :…”

Section: X-ray Photoelectron Spectroscopymentioning

confidence: 99%

Properties of GaP(001) surfaces treated in aqueous HF solutions

Morota

2007

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Chemically cleaned GaP͑001͒ surfaces in aqueous HF solutions have been studied using spectroscopic ellipsometry ͑SE͒, ex situ atomic force microscopy ͑AFM͒, x-ray photoelectron spectroscopy ͑XPS͒, wettability, and photoluminescence ͑PL͒ measurements. The SE data clearly indicate that the solutions cause removal of the native oxide film immediately upon immersing the sample ͑Յ1 min͒. The SE data, however, suggest that the native oxide film cannot be completely etch-removed. This is due to the fact that as soon as the etched sample is exposed to air, the oxide starts to regrow. The SE estimated roughness is ϳ1 nm, while the AFM roughness value is ϳ0.3 nm. The XPS spectra confirm the removal of the native oxide and also the presence of regrown oxide on the HF-etched GaP surface. The wettability measurements indicate that the HF-cleaned surface is hydrophobic, which is in direct contrast to those obtained from alkaline-cleaned surfaces ͑hydrophilic͒. A slight increase in the PL intensity is also observed after etching in aqueous HF solutions.

“…The native oxide thickness d ox can be estimated from the measured XPS intensity of oxide I ox and of GaP I GaP by the following expression: 43 d ox = ox cos lnͩ I ox GaP GaP I GaP ox ox + 1ͪ , ͑4͒…”

Section: X-ray Photoelectron Spectroscopymentioning

confidence: 99%

Properties of GaP(001) surfaces chemically treated in NH4OH solution

Morota

2006

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Chemically cleaned GaP͑001͒ surfaces in 25% NH 4 OH solution have been studied using spectroscopic ellipsometry ͑SE͒, ex situ atomic force microscopy ͑AFM͒, x-ray photoelectron spectroscopy ͑XPS͒, and wettability measurement techniques. The SE data clearly indicate that the solution causes removal of the native oxide film immediately upon immersing the sample. The SE data also indicate that when the native oxide film is completely etch removed, the resulting surface is still roughened. The estimated roughness thickness is ϳ1.2 nm, in excellent agreement with the AFM rms value ͑ϳ1.2 nm͒. The XPS spectra confirm the removal of the native oxide from the GaP surface. The XPS data also suggest a thin oxide overlayer, ϳ0.3 nm thick, on the etch-cleaned GaP surface. The wettability measurements indicate that the as-degreased surface is hydrophobic, while the NH 4 OH-cleaned surface is hydrophilic. This result is in direct contrast to those obtained from acid cleaned surfaces, which are usually hydrophobic. The origin of hydrophilicity may be singular and associated hydroxyl groups bonded on the GaP surface.