Penn‐like model calculations application to hydrogenated amorphous silicon films prepared by glow discharge

Abstract

Recent model calculations are studied of Ance e t al. concerning the valence electron density and hydrogen concentration in hydrogenated amorphous silicon films prepared by glow discharge decomposition of silane. This study is essentially necessitated by the fact that the model of Ance et al. yields values of Penn gap which are fairly large when compared to energies corresponding to peaks in the spectra of the imaginary part of the dielectric constant. Also a method is proposed to evaluate the density of the films. The densities hence determined are shown to be in accord with available experimental data. In the passing, results of the electronic polarizability of these films are also reported. Es werden die neueren Modellrechnungen von Ance e t nl. iiber die Dichte der Valenzelektronen undWasserstoffkonzentration in hydrogenisierten amorphen, durch Glimmentladungszersetzung von Silan hergest,ellten Siliziumschichten untersucht. Dies wird wesentlich durch die Tatsache erforderlich, daI3 das Modell von Ance et al. Werte fur das Penn-Gap liefert, die im Vergleich zu den Energien, die den Maxima in den Spektren des Imaginiirteils der Dielektrizitatskonstante entsprechen, ziemlich groB sind. Es wird eine Methode zur Berechnung der Schichtdichten vorgeschlagen. Die so bestimmten Dichten befinden sich in Ubereinstimmung mit vorhandenen experimentellen Werten. Des weiteren werden Ergebnisse der elektronischen Polarisierbarkeit dieser Schichten mitgeteilt.

Synchrotron radiation photoemission study of metal overlayers on hydrogenated amorphous silicon at room temperature

“…Moreover, one of the premises in the screening model is a substrate energy gap less than 2.2 eV and a static dielectric constant larger than 12 [79]. For a-Si:H sputtered at room temperature, the dielectric constant is about 7 [102]. Correspondingly, our system does not fit the criteria of the model.…”

Polarizability Studies of Amorphous Silicon

“…Since, in the optical range, the dielectric constant arises essentially from the electronic polarizability, the electronic polarizability a, may also be evaluated using the relation where N e is the number of atoms per unit volume of type e. For amorphous silicon, there have been very few measurements of density reported in literature. Therefore, an approximate method was proposed earlier for the determination of the density [ 3 ] . This method was shown to explain fairly well the change in effective number of electrons contributing to optically induced electronic transitions as well as the experimental values of the density of Tanielian x loz3 ~m -~,…”

“…The density e is then defined as [3] where ea-si and pc-si are the densities of amorphous and crystalline Si, respectively, n, and n, are the valence electron densities of amorphous and crystalline Si, reapectively (n, = 2 x 1023 cm-9, and ec-si = 2.33 g cm-3. To determine the molecular weight of amorphous silicon, we define…”

“…In all these calculations, we consider that the amorphous films are a mixture of the component materials. For calculations of the total polarizability, since the densities of the films are not known experimentally, they are evaluated from spectroscopic models like that of Ravindra et al [3].…”