Recent applications of spectroscopic phase modulated ellipsometry, from UV to IR, to the study of the growth of plasma deposited thin film semiconductors like amorphous (a-Si:H) and microcrystalline ((mu) c-Si) silicon are reviewed. The high sensitivity of this technique is emphasized. In the UV range, the ability of kinetic ellipsometry, with fast time resolution, to study the complex growth mechanism of (mu) c-Si is illustrated. In particular, the importance of hydrogen etching during (mu) c-Si growth is evidenced. In the IR, the hydrogen incorporation during a-Si:H growth can be precisely investigated. Photoelectronic quality a- Si:H films grow beneath a hydrogen rich overlayer (1-3 monolayers thick) containing SiH2, the hydrogen being bonded as SiH in the bulk material. 2.2 +/- 0.5 X 105 V/cm, which agrees very well with theory. thick. We show that this heterojunction is barely distinguishable in a PR measurement. Nevertheless, at room temperatutric field on the photoreflectance lineshape is discussed. The observed effect may be applied as an optical measurement of the electric field and the carrier concentration within a depth of about 17 nm from the surface/interface. phonon modes; InAs-like TO (226 cm-1), InAs-like LO (233 cm-1), GaAs-like TO (255 cm-1), and GaAs-like LO (270 cm-1), and one alloy disorder mode R* (244 cm-1) for InGaAs on InP. For all five Raman features stoichiometry, in terms of the RD response and the materials properties, which was recently demonstrated for VCE growth. Finally, we compare the quality and the character of real-time RD-detected growth oscillations as obtained for CBE, VCE, and MOVPE growth.