Raman spectroscopy is used to study GaAs heavily doped with carbon. Hole concentrations in these samples range from 2.3×1019 to 1×1020 cm−3. Three main Raman features are investigated: the longitudinal-optic (LO) phonon mode, the substitutional carbon-at-arsenic local-vibrational mode, and the coupled plasmon–LO phonon present due to the interaction between the LO phonon and the free carriers. Only one allowed phonon-like coupled mode is observed due to the large plasmon damping and high effective carrier masses. The coupled mode is seen to systematically redshift as carrier concentration increases. This behavior is described by a model which includes the effects of high hole concentrations on the dielectric function and an additional shift in the optic phonon we tentatively attribute to carbon size effect. The local vibrational mode intensity is found to be directly proportional to the carrier concentration p. Interestingly, the local mode intensity shows good correlation with that of the coupled plasmon–LO phonon mode as a function of p. The ratio of the coupled plasmon–LO phonon mode intensity to that of the LO phonon is found to be directly proportional to the carrier concentration.

An examination of low-temperature photoluminescence from chemically thinned InP illustrates the effect of multiple absorption and reemission of photons in bulk liquid-encapsulated Czochralski grown material. Luminescence spectra show that such photon recycling dramatically increases the nonequilibrium carrier density in the material and causes excess carrier distribution to penetrate tens of micrometers beneath the sample surface, an order of magnitude more than a diffusion length. Nonequilibrium carriers also penetrate deeper with increasing excitation levels as a consequence of more efficient radiative recombination. Although these effects have not been widely recognized, they have important consequences in the interpretation of luminescence spectra and the design of electronic and optical devices based on InP that are sensitive to minority-carrier diffusion lengths.

A commonly observed luminescence band in InP near 1.35 eV has been studied in detail. The dependence of the transition energy on sample temperature and excitation power density indicates the band results from a donor-to-acceptor pair transition involving a donor level with an activation energy of ∼33 meV. Luminescence spectra from samples implanted with Si, Al, or P show that the donors responsible for the band are native defects or complexes that result from radiation damage. These results do not support previous assignments of the 1.35-eV band to transitions involving various impurities.

While epitaxial CaF2 films grown on Si(111) at temperatures above 550 °C exhibited flat capacitance-voltage (C-V) curves, suggesting a pinned CaF2/Si(111) interface, we have observed unpinned C-V curves from as-deposited epitaxial CaF2 grown at 300 °C. Our results demonstrate that C-V characteristics of CaF2/Si(111) are determined by the thermal history, rather than the crystalline quality, of the CaF2 film. Correlations among CaF2/Si interface state density, thermal stress, and atomic bonding at the interface are discussed.

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