Influence of microstructure on the Urbach edge of amorphous SiC:H and amorphous SiGe:H alloys

Mahan, A. H.; Menna, P.; Tsu, Raphael

doi:10.1063/1.98721

Cited by 65 publications

(18 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[31] Since films containing more C H also contain more clustered H, the X-ray beam increasingly samples these clustered H complexes, and the broader XRD FWHM's for these films indicates that the spatial regions of NMR clustered H are less well ordered on a medium range scale. For the extensively investigated a-SiC:H system, deposited using silane and methane gas mixtures, [27,28] the valence band tail was observed to broaden with increasing (larger vacancy-type) microvoid densities (decreased structural order), [41] a trend consistent with the theoretical calculations for vacancy incorporation into a-Si.…”

Section: Resultssupporting

confidence: 69%

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Mahan

Williamson

et al. 2009

Adv Funct Materials

View full text Add to dashboard Cite

Utilizing the concepts of a critical crystallite size and local film inhomogeneity, it is shown that nucleation in thermally annealed hydrogenated amorphous silicon occurs in the more well ordered spatial regions in the network, which are defined by the initial inhomogeneous H distributions in the as‐grown films. Although the film H evolves very early during annealing, the local film order is largely retained in the still amorphous films even after the vast majority of the H is evolved, and the more well ordered regions which are the nucleation center sites for crystallization are those spatial regions which do not initially contain clustered H, as probed by H NMR spectroscopy. The sizes of these better ordered regions relative to a critical crystallite size determine the film incubation times (the time before the onset of crystallization). Changes in film short range order upon H evolution, and the presence of microvoid type structures in the as grown films play no role in the crystallization process. While the creation of dangling bonds upon H evolution may play a role in the actual phase transformation itself, the film defect densities measured just prior to the onset of crystallization exhibit no trends which can be correlated with the film incubation times.

show abstract

Section: Resultssupporting

confidence: 69%

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Mahan

Williamson

et al. 2009

Adv Funct Materials

View full text Add to dashboard Cite

show abstract

“…In previous publications E 0 , obtained by photothermal deflection spectroscopy ͑PDS͒, was plotted for a variety of amorphous systems (a-Si:H, a-SiC:H, a-SiGe:H) versus not only the infrared microstructure fraction parameter R*, but also the density deficiency ͑from flotation density measurements͒ as well as the SAXS microvoid volume fraction V f . [35][36][37][38] It is noted that these investigations covered a range of V f 's ͑and E 0 's͒ much larger than that for the present films. Although the methodology used in those publications to obtain the E 0 values has since been greatly improved ͑i.e., the CPM technique yields significantly narrower E 0 s when both CPM and PDS measurements are made on the same device quality a-Si:H films͒, 39 the trends were nevertheless clear in that both plots yielded an increase in E 0 for all samples with an increase in microstructure measured either by infrared ͑IR͒, flotation, or SAXS.…”

Section: Discussionmentioning

confidence: 77%

Structural properties of hot wire a-Si:H films deposited at rates in excess of 100 Å/s

Mahan

Williamson

et al. 2001

Journal of Applied Physics

Self Cite

View full text Add to dashboard Cite

The structure of a-Si:H, deposited at rates in excess of 100 Å/s by the hot wire chemical vapor deposition technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). The films examined in this study were chosen to have roughly the same bonded H content CH as probed by infrared spectroscopy. As the film deposition rate Rd is increased from 5 to >140 Å/s, we find that the short range order (from Raman), the medium range order (from XRD), and the peak position of the H evolution peak are invariant with respect to deposition rate, and exhibit structure consistent with a state-of-the-art, compact a-Si:H material deposited at low deposition rates. The only exception to this behavior is the SAXS signal, which increases by a factor of ∼100 over that for our best, low H content films deposited at ∼5 Å/s. We discuss the invariance of the short and medium range order in terms of growth models available in the literature, and relate changes in the film electronic structure (Urbach edge, as-grown defect density) to the increase in the SAXS signals. We also note the invariance of the saturated defect density versus Rd, measured after light soaking, and discuss possible reasons why the increase in the microvoid density apparently does not play a role in the Staebler–Wronski effect for this type of material.

show abstract

“…As this particular behavior is so widely observed, it would appear that the origin of this effect is depending on a single universal mechanism. In spite of past extensive experimental [20][21][22][23][24][25] and theoretical [26][27][28][29][30][31][32][33][34][35][36][37] investigations, the microscopic origin of the absorption tail continues to be a matter of research. In crystalline lattices U-M tails originate from: (i) a temperature induced disorder reflecting the thermal occupancy of phonon states [20,26], (ii) temperature independent static structural disorder associated with impurities, dislocations, stacking faults, etc.…”

Section: Resultsmentioning

confidence: 99%

Urbach-Martienssen Tails in the Absorption Spectra of Layered Ternary Semiconductor TlGaS2

Abay

Güder

Efeoǧlu

et al. 2001

phys. stat. sol. (b)

View full text Add to dashboard Cite

The dependence of the absorption coefficient on the photon energy and sample temperature near the fundamental absorption edge (AE) was investigated for TlGaS 2 layered semiconductor crystals. The exponential absorption tails observed in the 10-340 K temperature range were interpreted as Urbach-Martienssen (U-M) tails. From the analysis of these tails, characteristic Urbach parameters were determined. The results lead to the conclusion that the temperature dependence of the absorption tails near the fundamental AE of TlGaS 2 is the result of thermal disorder.

show abstract

Influence of microstructure on the Urbach edge of amorphous SiC:H and amorphous SiGe:H alloys

Cited by 65 publications

References 19 publications

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Structural properties of hot wire a-Si:H films deposited at rates in excess of 100 Å/s

Urbach-Martienssen Tails in the Absorption Spectra of Layered Ternary Semiconductor TlGaS2

Contact Info

Product

Resources

About