Photoluminescence and optically detected magnetic resonance of a-Si1−xCx:H films

Liedtke, S.; Lips, K.; Bort, M.; Jahn, Karin; Fuhs, W.

doi:10.1016/0022-3093(89)90637-6

Cited by 42 publications

(10 citation statements)

References 6 publications

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“…At the same time, the width of the PL bands varies from 250 to 150 nm. Our observations agree nicely with the results of other laboratories who have conducted extensive studies on this material (Siebert et al 1987;Liedtke et al 1989;Tessler & Solomon 1995).…”

Section: Resultssupporting

confidence: 82%

Crystalline silicon nanoparticles as carriers for the Extended Red Emission

Ledoux

Guillois

Huisken³

et al. 2001

A&A

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Abstract.In an attempt to determine the carrier of the Extended Red Emission (ERE), we have investigated a series of amorphous and crystalline materials: natural coal, amorphous hydrogenated carbon, amorphous hydrogenated silicon carbide, porous silicon, and crystalline silicon nanoparticles. The photoluminescence (PL) behavior of various samples of these materials upon excitation with UV light was studied at room temperature focusing on both the wavelength dependence of the photoluminescence and the PL yield. For some samples the yield is by far too low, other samples do not comply with the characteristic wavelength range of ERE. Only the samples of nanocrystalline silicon (porous silicon and silicon nanoparticles) reveal PL properties that are compatible with the astronomical observations. Besides this experimental evidence, we will supply additional arguments leading to the conclusion that silicon nanoparticles should be seriously considered as an attractive carrier for the Extended Red Emission.

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Section: Resultssupporting

confidence: 82%

Crystalline silicon nanoparticles as carriers for the Extended Red Emission

Ledoux

Guillois

Huisken³

et al. 2001

A&A

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“…Excitation of a-C : H by band edge photons will tend to create an electron and hole in the same cluster where they will remain bound by the surrounding sp3 barrier. This binding favours intracluster radiative recombination, giving luminescence in a-C : H and carbon-rich a-Si, -xCx : H which is efficient and largely independent of temperature and electric field, as observed previously (Lin and Feldman 1982, Siebert, Carius, Fuhs and Jahn 1987, Liedkte et al 1989, Vassilyev et al 1989. In contrast, luminescence in a-Si : H and siliconrich a-Si, -&: H is strongly quenched at moderate temperatures (Siebert et al 1987, Vassilyev et al 1989.…”

supporting

confidence: 54%

“…In contrast, luminescence in a-Si : H and siliconrich a-Si, -&: H is strongly quenched at moderate temperatures (Siebert et al 1987, Vassilyev et al 1989. Liedtke et al (1989) noted that recombination rates in carbon-rich a-Si, -,C,:H alloys do not correlate with the defect density, as they do in The presence of localized states above the optical band edges in a-C : H allows luminescence to occur above its optical gap. Figure 5 compares the peak luminescence to occur above its optical gap.…”

mentioning

confidence: 90%

π-bonded clusters in amorphous carbon materials

Robertson

1992

Philosophical Magazine B

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Total energies favour a segregation of the sp2 sites in amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C : H) into sp2-bonded clusters embedded in a sp3-bonded matrix. The size of the clusters determines the local bandgap. The presence of clusters forces the mobility edges further into the bands. Clustering also introduces strong symmetrical fluctuations of the band edges. This causes intracluster transitions between localized and localized states to become allowed. The effect of such clustering on the luminescence properties, the resonant Raman spectra, the Urbach tail and the subgap defect optical absorption of a-C: H is discussed. The sp2 sites form mainly sixfold rings within the clusters. The presence of a small fraction of adjacent fivefold and sevenfold rings washes out the thirdneighbour peak at 2%4A in the radial distribution function of sputtered a-C.Amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C : H) contain both sp3 and sp2 carbon sites, with 1-5% sp3 sites in evaporated a-C (Green, McKenzie and Lukins 1990) and sputtered a-C (Cho et al. , Pan et al. 1991, and 40-70 sp3 sites in plasma-deposited a-C : H (Koidl et al. 1990, Tamor, Vassell andCarduner 1991). The sp3 sites and sp2 sites are connected together by (T bonds which form the skeleton of the random network. The sp2 sites also possess x states which form x bonds with neighbouring sp2 sites. The x states of n bonds lie closer to the Fermi level E , than do the c states; so the n: states form both the valence-and the conduction-band-edge states in a-C and a-C : H and consequently they control the electronic properties of both materials (Robertson 1986, Robertson and OReilly 1987). Analysis of the energetics of x bonding suggests that the sp2 sites will segregate into graphitic clusters embedded in a sp3-bonded matrix. The difference between the bandgaps of the sp2-and sp3-bonded regions produces very large fluctuations in the local bandgap (Robertson 1988). This paper describes the consequences of such fluctuations and clustering and discusses the evidence that the clustering occurs.The clustering of sp2 sites arises from the non-local energetics of their x bonding.The energetics of c and n bonds are separable, to first order. The stronger (T bonds form the skeleton of the network. The two-centre quality of the c bonds allows their total energy to be written as the sum of the energies of the individual bonds; that is it is a local function. The x bonds are more complex. They can form two-centre bonds such as the C=C bond in ethylene. They can also form multicentre or resonant bonds as in polyacetylene, benzene or graphite. This resonant character prevents the total x bond energy being expressed as a sum of two-centre terms as it adds non-local (off-site or longer-range) terms. The energetics of x bonding favours sp2 sites forming sixfold ring aromatic species such as benzene, rather than chain (olefinic) species such as ethylene or polyacetylene. Their energetics also favours the fusing of sixfold rings into polyaromati...

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“…Some groups have proposed that there is a basic change in the structure of a-CH/Si alloys near a carbon atomic fraction C/(C+Si) of 0.5 [7,8]. At carbon fractions higher than 0.5 the structure becomes polymer like.…”

Section: Introductionmentioning

confidence: 98%