We report values of pseudodielectric functions $〈\ensuremath{\epsilon}〉=〈{\ensuremath{\epsilon}}_{1}〉+i〈{\ensuremath{\epsilon}}_{2}〉$ measured by spectroscopic ellipsometry and refractive indices $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{n}=n+ik$, reflectivities $R$, and absorption coefficients $\ensuremath{\alpha}$ calculated from these data. Rather than correct ellipsometric results for the presence of overlayers, we have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. Our results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atmosphere regardless of the technique used to obtain the data. Differences among our data and previous results can generally be understood in terms of inadequate sample preparation, although results obtained by Kramers-Kronig analysis of reflectance measurements often show effects due to improper extrapolations. The present results illustrate the importance of proper sample preparation and of the capability of separately determining both ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ in optical measurements.

Dielectric functions and optical parameters of Si, Ge, GaP, GaAs, GaSb, InP, InAs, and InSb from 1.5 to 6.0 eV

A new reversible photoelectronic effect is reported for amorphous Si produced by glow discharge of SiH4. Long exposure to light decreases both the photoconductivity and the dark conductivity, the latter by nearly four orders of magnitude. Annealing above 150 °C reverses the process. A model involving optically induced changes in gap states is proposed. The results have strong implications for both the physical nature of the material and for its applications in thin‐film solar cells, as well as the reproducibility of measurements on discharge‐produced Si.

Reversible conductivity changes in discharge‐produced amorphous Si

The paper examines states in the gap in amorphous silicon and chalcogenides and their effect on photoconductivity, luminescence and drift mobility. It is supposed that carriers in an ‘ideal’ glassy semiconductor without defects would move by hopping at the band edge at low temperatures and by excitation to a mobility edge at high temperatures, and that the carriers do not form polarons; the results of Spear and co-workers (e.g. Spear 1974 a) for glow-discharge-deposited silicon and of Nagels, Callearts and Denayer (1974) for quenched As2Te3 containing silicon are considered. The effectively zero value of the Hall coefficient in the hopping regime is discussed. States in the gap are supposed to be due to dangling bonds which may form pairs at divacancies; if the concentration is high, these may have a predominating effect on the conductivity and in this case polaron-type hopping could occur, both for chalcogenides and for silicon. For the chalcogenides (in contrast to silicon), it is proposed, ada...

States in the gap and recombination in amorphous semiconductors

Refractive index data for silicon and germanium were searched, compiled, and analyzed. Recommended values of refractive index for the transparent spectral region were generated in the ranges 1.2 to 14 μm and 100–740 K for silicon, and 1.9 to 16 μm and 100–550 K for germanium. Generation of these values was based on a dispersion equation which best fits selected data sets covering wide temperature and wavelength ranges. Temperature derivative of refractive index was simply calculated from the first derivative of the equation with respect to temperature. The results are in concordance with the existing dn/dT data.

Refractive index of silicon and germanium and its wavelength and temperature derivatives

Kinetics of solid phase crystallization in amorphous silicon

Structural, Optical, and Electrical Properties of Amorphous Silicon Films

Experimental data on photoconductivity and photoluminescence of amorphous chalcogenides are reviewed and are examined by means of a simple model in which most of the carriers created by the light drop into localized states before recombining bimolecularly.

Photoconductivity and photoluminescence of amorphous chalcogenides

We have studied the resistivity, optical absorption and photoconductivity of amorphous As 2 Te 3 films prepared by e-beam evaporation of bulk material on substrates cooled to 77°K. Film thickness were typically several thousand angstroms, and chemical analysis indicated that the films were approximately stoichiometric. The films were stable up to about 450°K above which temperature they tended to devitrify. The resistivity between 200 and 400°K showed an exponential dependence of the resistivity on inverse temperature with an activation energy of 0.4 eV suggesting a “conductivity gap” of 0.8 eV. Optical absorption constants were determined for values of α between 10 4 and 2 × 10 5 cm −1 in the energy range from 1.0 to 1.6 eV. Photoconductivity measurements yielded an upper limit of 5 × 10 −8 sec for the recombination time and a lower limit of 0.3 cm 2 /V sec for the mobility of photocarriers.

K. Weiser

Papers

Structural, Optical, and Electrical Properties of Amorphous Silicon Films

Photoconductivity and photoluminescence of amorphous chalcogenides

Electrical and optical properties of amorphous As2Te3 films

On the relation between optical, electrical, and structural properties of amorphous silicon☆