Infrared Spectrum and Structure of Hydrogenated Amorphous Silicon

Abstract

The ir absorption spectrum of hydrogenated amorphous silicon is discussed in the context of structural models for this material. It is shown that the integrated strength of the bond stretching bands in hydrogenated amorphous silicon cannot be used to determine the hydrogen concentration because the local effective charge for ir absorption is a function of hydrogen concentration and sample preparation. The effective charge for the wagging-rocking-rolling vibrations a t 640 cm-', however, is independent of hydrogen concentration and sample preparation. Hence the integrated strength of this band can be used to measure the hydrogen concentration provided the proportionality constant is determined empirically. Changes in the ir absorption bands as a function of isochronal annealing temperature show that two different types of bonds contribute t o the bond stretching band a t 2100 cm-l. The bond bending bands a t 890 and 840 cm-1 are associated with one of the bonds producing the 2100 cm-' stretching band. The relative strengths of the 890 and 840 cm-1 bands to the 2100 cm-l band depend strongly on the film preparation method: the glow discharge produced films show much stronger bending bands than those produced by r f sputtering. A structural model for hydrogenated amorphous silicon is presented in which a Maxwell-Garnetttype local field correction, which is dependent on the dipole location within a microvoid and the shape of the microvoid, is used to explain the data.Das IR-Absorptionsspektrum von hydrogenisiertem, amorphem Silizium wird im Zusammenhang mit Strukturmodellen fiir dieses Naterial untersucht. Es wird gezeigt, daB die integrale Starke der ,,bond-stretching"-Banden in hydrogenisiertem, amorphem Silizium nicht fur die Bestimmung der Wasserstoffkonzentration benutzt werden kann, weil die lokale effektive Ladung fur die IR-Absorption eine Funktion der Wasserstoffkonzentration und Probenpraparation ist. Die effektive Ladung fur die ,,wagging-rocking-rolling"-Schwingungen bei 640 cm-l ist jedoch unabhingig von der Wasserstoffkonzentration und Probenpraparation. Somit kann die integrale Starke dieser Bande benutzt werden, um die Wasserstoffkonzentrtion zu messen, vorausgesetzt, daB die Proportionalitatskonstante empirisch bestimmt wird. Anderungen in den IR-Absorptionsbanden in Abhangigkeit von der isochronen Temperungstemperatnr zeigen, daB zwei unterschiedliche Bindungsarten zur ,,bond-stretching"-Bande bei 2100 cm-1 beitragen. Die ,,bond-bending"-Banden bei 890 und 840 cm-l sind mit einer der Bindungen verknupft, die die 2100 cm-'-Stretching-Bande hervorrufen. Die relativen Starken der 890-und 840-cm-l-Banden zur 2100 cm-l-Bande hangen stark von der Schichtherstellungsmethode ab : die durch Glimmentladung hergestellten Schichten zeigen vie1 starkere Bindungsbanden als die durch HF-Sputtern hergestellten. Ein Strukturmodell fur hydrogenisiertes, amorphes Silizium wird angegeben, in dem eine lokale Feldkorrektur vom Maxwell-Garnett-Typ benutzt wird, die von der Dipollokalisierung im Innern eines Mikrohohlraume...

Light induced electrical and macroscopic changes in hydrogenated polymorphous silicon solar cells

“…In addition, not only circular shaped holes, but also many irregular shaped holes are found in SEM images. It implies that the macroscopic changes are similar to the buckling observed when films are annealed at high temperature [34,40,45,46].…”

Hydrogen in amorphous and microcrystalline silicon films prepared by hydrogen dilution

“…This calibration constant correlates the strength of the IR-absorption bands due to the Si-H vibrations with the hydrogen content. It has been found for a-Si:H material 4 that the calibration constant of the integrated strength of the rocking-wagging-rolling vibrations around 640 cm Ϫ1 is independent of hydrogen content and of sample preparation. However, it is not evident that the proportionality constant formerly found still remains valid when the a-Si:H network is replaced by the hydrogenated microcrystalline silicon material as is the case in our study.…”

Effects of prior hydrogenation on the structure and properties of thermally nanocrystallized silicon layers

“…In this respect, the 2000 cm Ϫ1 vibration is attributed to isolated monohydrides ͑Si-H͒, while the 2090-2100 cm Ϫ1 modes can be ascribed to dihydrides (Si-H 2 ) and/or clustered monohydride species. [10][11][12] The detection of Si-H 2 bending vibrations and the modes of (Si-H 2 ) n chains at around 890 and 840 cm Ϫ1 , respectively, 13 confirms the formation and, therefore, the contribution of Si-H 2 in the spectra shown in Fig. 1͑b͒.…”