J. Ortega-Gallegos

A multichannel reflectance anisotropy spectrometer for epitaxial growth monitoring

We report on a reflectance anisotropy (RA) spectrometer capable of measuring reflectance spectra on the 100 ms time-scale and sensitivity in the upper 10−4 range. A multichannel lock-in amplifier was used to acquire 32 wavelengths RA spectra covering the 2.25–3.85 eV photon energy range, where the E 1 and transitions of GaAs and other technologically relevant III–V semiconductor are located. The RA spectra recorded during the first stages of the GaAs homoepitaxial deposition are presented for the first 0.38 monolayers of growth, showing significative changes in the lineshape with low noise. Thanks to the capabilities of this instrument, it is possible to observe in detail, in terms of the evolution of RA spectra, the processes carried out during the migration of surface reconstruction between two stable phases present in the homoepitaxial growth of GaAs.

One electron and discrete excitonic contributions to the optical response of semiconductors around E 1 transition: analysis in the reciprocal space

Spectroscopic ellipsometry (SE) has been utilized during the past decades for the measurement of the dielectric function of semiconductors. By using SE, interband critical point parameters such as energy gaps and broadenings are routinely determined. In the direct-space analysis approach, these parameters are known by taking the numerical energy derivatives of the dielectric function and fitting the spectra by using a Lorenzian line shape. However, in many cases the noise of the spectra does not allow the determination of such parameters as precisely as they are needed. Additionally, the determination of the character of the transitions, which is uncorrelated (one electron) or correlated (discrete excitons), is necessary for the analysis of the dielectric function. For instance, different values for the broadening parameter are obtained by using uncorrelated or correlated line shapes. We use a reciprocal-space analysis instead of the most commonly used direct-space analysis for determining without any uncertainty the character and, consequently, a precise value of the broadening parameter of the E1 transitions of GaP, GaAs, Si, CdTe, GaSb, HgTe, and an alloy semiconductor: Cd0.18Hg0.82Te.