Berlin 2005 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 21: FV-internes Symposium „Optische Spektroskopie von dünnen Schichten und Grenzfl
ächen"

DS 21.1: Hauptvortrag

Dienstag, 8. März 2005, 09:45–10:30, TU HS110

Real-time optical diagnostics for epitaxial growth — •D. E. Aspnes — Physics Dept., NC State University, Raleigh, NC 27695-8202

Optical diagnostics are currently the only means of assessing the epitaxial growth of materials in the relatively high pressure environments characteristic of organometallic chemical vapor deposition (OMCVD). These diagnostic techniques include reflectance-anisotropy (-difference) spectroscopy (RAS/RDS) for determining surface reconstructions and terminations, laser light scattering (LLS) for detecting the onset of microscopic roughness, and spectroscopic ellipsometry (SE) for measuring compositions and thicknesses of depositing layers. As a result of the needs of the semiconductor industry, the capabilities of SE in particular have been significantly enhanced in the last several years, with the result that the rotating-polarizer and -analyzer configurations that dominated SE for the last 30 years are being replaced by rotating-compensator designs. When coupled with photodiode-array detectors, rotating-compensator systems allow highly accurate SE data to be obtained at rates of the order of Hz, significantly extending capabilities for growth assessment as well. As a general example I discuss the use of SE and LLS in an integrated OMCVD reactor to optimize the heteroepitaxial growth of GaSb on GaAs, which allowed the production of material where interface defects were limited to those needed to accommodate the 7.8% lattice mismatch between substrate and overlayer. Analysis of data obtained at 1 s (0.2 nm growth) intervals during the critical initial stages of heteroepitaxy showed that in this case heteroepitaxy initiated as GaSb islands in GaAs.