Thermoelectric power in undoped hydrogenated polymorphous silicon

Thermoelectric power and conductivity measurements have been made as a function of temperature on a new nanostructured material, hydrogenated polymorphous silicon (pm-Si:H). The thermoelectric power is negative, so electrons are the dominant carriers. The activation energy of the thermopower is less than that of the dark conductivity. However, the short-circuit Seebeck current activation energy agrees with the conductivity-activation energy. These results are consistent with a model involving long-ranged fluctuations at the mobility edges. The magnitude of the fluctuations is larger than that measured in highly-doped hydrogenated amorphous silicon (a-Si:H) in relation to the peculiar structure of pm-Si:H. (C) 2000 Elsevier Science S.A. All rights reserved

Determination of the midgap density of states and capture cross-sections in polymorphous silicon by space-charge-limited conductivity and relaxation

A new type of material consisting of an amorphous silicon matrix, in which silicon nanoparticules are embedded, has recently been obtained. This material, named polymorphous silicon (pm-Si), exhibits enhanced transport and stability properties with respect to hydrogenated amorphous silicon (a-Si:H). In order to progress in the understanding of such improved properties, we combine space-charge-limited current and space-charge relaxation measurements which allow us to show that the density of states at the Fermi level and their capture cross sections in pm-Si are at least ten times and five times lower respectively than in a-Si:H. This is in good agreement with photoconductivity results

CORRELATION BETWEEN CONDUCTIVITY, ELECTRON SPIN RESONANCE AND OPTICAL ABSORPTION IN RF SPUTTERED SiO2 FILMS

This article reports on conductivity, ESR and optical absorption spectra obtained on rf sputtered SiO2 films. Measurements performed in different ambiences show that H2O considerably alters the physical properties of the films. The first pumping after the elaboration of a film reduces both, the conductivity and the total ESR signal, while the optical absorbance is increased. When wet air is again admitted the conductivity rapidly in creases while ESR and optical spectra are unchanged. It is concluded that charge carriers are introduced by H2O independently of intrinsic defects. Complementary experiments are suggested to investigate the possible influence of intrinsic defects on transport phenomena

Concentrations des porteurs et champ électrique le long d'un échantillon isolant ou semiconducteur. Développements des solutions stationnaires jusqu'au second ordre. Cas des faibles potentiels

Quand une différence de potentiel continue V est appliquée à un isolant ou un semiconducteur muni d'électrodes bloquantes, des zones de charge d'espace s'établissent près de ces électrodes. La solution du problème, limitée au premier ordre en V est connue ; dans certains cas, il peut être utile d'avoir cette solution développée jusqu'au second ordre, en particulier lors de la recherche de solutions dépendant du temps. C'est pourquoi dans cet article, les expressions développées jusqu'au second ordre en V, des densités de porteurs et du champ électrique en tout point de l'échantillon sont calculées

Concentrations des porteurs et champ électrique le long d'un échantillon isolant ou semiconducteur. Développements des solutions stationnaires jusqu'au second ordre. Cas des faibles potentiels

When a dc potential difference V is applied to an insulator or a semiconductor with two blocking electrodes, space charge takes place near the electrodes. The solution of this problem limited to the first order in V is known, in many cases it may be useful to have this solution developed up to the second order, specially when we search time dependent solutions. Therefore in this paper the expressions of carrier densities and electric field in all the points of the sample, developed up to the second order in V, are calculated.Quand une différence de potentiel continue V est appliquée à un isolant ou un semiconducteur muni d'électrodes bloquantes, des zones de charge d'espace s'établissent près de ces électrodes. La solution du problème, limitée au premier ordre en V est connue ; dans certains cas, il peut être utile d'avoir cette solution développée jusqu'au second ordre, en particulier lors de la recherche de solutions dépendant du temps. C'est pourquoi dans cet article, les expressions développées jusqu'au second ordre en V, des densités de porteurs et du champ électrique en tout point de l'échantillon sont calculées

Links between hydrogen bonding, residual stress, structural properties and metastability in hydrogenated nanostructured silicon thin films

We present a systematic study of the local hydrogen bonding in hydrogenated polymorphous silicon thin films (pm-Si:H), a heterogeneous material deposited on the edge of crystallinity, by means of Fourier transform infrared spectroscopy. A vibrational mode at similar to2030 cm(-1) is reported and attributed to hydrogen atoms bonded in hydrogen-rich regions present at the interface between ordered regions and the amorphous matrix. This assignment is found to be in good agreement with previous spectroscopic ellipsometry and Raman spectroscopy studies. Combined with stress measurements we draw a picture of the nanostructure of pm-Si:H films, namely a two-domain material exhibiting: (i) large fluctuations of H content, (ii) a high mass density and (iii) the coexistence of highly strained crystalline phases with a relaxed amorphous matrix. Unexplained optoelectronic properties and metastability phenomena can also be accounted for by this picture

Structural properties depicted by optical measurements in hydrogenated polymorphous silicon

Hydrogenated polymorphous silicon (pm-Si:H) is a new material obtained by plasma-enhanced chemical vapour deposition by running the plasma close to powder formation. Preliminary studies have revealed the presence of silicon nanocrystallites embedded in an amorphous matrix but only in a limited range of deposition conditions. In this work we have investigated the structural properties of such films by means of spectroscopic optical measurements. The analysis of transmission spectra in the transparent region has shown that pm-Si:H films have indeed a more ordered structure than state-of-the-art hydrogenated amorphous silicon (a-Si:H) films. This has been observed in the whole range of deposition conditions leading to pm-Si:H films. On a final point the implication of structural properties on the excellent optoelectronic properties previously reported in pm-Si:H films is discussed

Transferts de charges dans un milieu diélectrique. Etude de courants transitoires

On a calculé l'expression du courant transitoire dans un milieu diélectrique possédant deux types de porteurs d'égale mobilité ou un seul type de porteurs mobiles. Les électrodes sont supposées bloquantes. Lors de l'application d'un échelon de tension de faible amplitude, l'évolution du courant est régie par une seule constante de temps, proportionnelle au temps de relaxation diélectrique et au rapport L/LD (L longueur de l'échantillon, LD longueur de Debye)

Effets capacitifs liés à la charge d'espace dans un semi-conducteur avec électrodes bloquantes

The equivalent complex dielectric constant of a semiconductor is calculated, taking into account space charges produced by electron transfer between donor level and conduction band.On a calculé la constante diélectrique complexe équivalente d'un semi-conducteur en faisant intervenir les charges d'espace liées aux transferts d'électrons entre le niveau donneur et la bande de conduction