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

We compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of the structure of these materials. For the full range of carbon‐hydrogen alloys, including so‐called ‘‘amorphous diamond,’’ hydrogenated ‘‘diamondlike’’ carbon, and plasma‐polymers, a simple parametrization of the Raman spectrum in the usual 1000 cm−1 to 2000 cm−1 range can be used as a reliable predictor of hydrogenation and other properties (e.g., optical gap, hardness). Raman features in the 200 cm−1 to 1000 cm−1 range, a spectral region not usually reported for carbon films, may also be used as an indicator of hydrogenation. These growth method independent correlations greatly enhance the utility of Raman spectroscopy as a non‐destructive characterization and process control tool.

Raman ``fingerprinting'' of amorphous carbon films

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

The crystallization and compound formation temperature of vacuum deposited amorphous Si (and Ge) while in contact with various crystalline metals as a thin film sandwich are investigated by electron microscopy and electron diffraction. The results show that in simple eutectic systems the Si crystallizes at 0.72 (and Ge at approximately 0.65) of the eutectic temperature expressed in degrees Kelvin. Compounds are formed generally by the more rapid diffusion of Si into the metal.

Metal contact induced crystallization in films of amorphous silicon and germanium

We report the results of measurement and analysis of the electrical conductivity as a function of temperature and anneal for amorphous silicon films. The resistivity of the films between 77 and 300°K increasesc with annealing. Refractory electrodes were used. The extrapolated portions of T − 1 4 fits to the log of the conductivity give physically unreasonable parameters for the T − 1 4 formula.

Electrical conduction in evaporated amorphous silicon films

Raman and infrared spectroscopy yield detailed information about the vibrational modes of solids. Photoelectron spectroscopy gives corresponding information on valence and core electronic states. From these spectroscopies the nature of the local atomic order can be inferred. Applications of these methods are illustrated for prototype tetrahedral and chalcogenide amorphous semiconductors. The retention of the crystalline short range order is manifested in the vibrational spectrum of pure amorphous silicon and the III–V compounds. Similar conclusions are obtained from the photoelectron spectra along with additional information on ring configurations. For Se and chalcogenide compounds (e.g. GeTe) vibronic and electronic spectral reveal differences between amorphous and crystalline short range orders. In addition to these intrinsic structures, the local environments and effects of additives, such as hydrogen and conventional dopants in amorphous silicon, are discussed.

Local order as determined by electronic and vibrational spectroscopy: Amorphous semiconductors

A phenomenological explanation of Raman scattering in amorphous Si, Ge and III–V semiconductors is given, using Si as an example. Several applications of Raman scattering to the study of amorphous materials are discussed.

M.H. Brodsky

Papers

Structural, Optical, and Electrical Properties of Amorphous Silicon Films

Metal contact induced crystallization in films of amorphous silicon and germanium

Electrical conduction in evaporated amorphous silicon films

Local order as determined by electronic and vibrational spectroscopy: Amorphous semiconductors

Raman scattering in amorphous Si, Ge and III–V semiconductors