SPECTROSCOPIC ELLIPSOMETRY AND PHOTOLUMINESCENCE FROM SI1-XGEX ALLOYSGROWN BY ATMOSPHERIC-PRESSURE CHEMICAL-VAPOR DEPOSITION

Si1-xGex layers grown using atmospheric pressure chemical vapor deposi tion have been characterized using both room temperature spectroscopic ellipsometry (SE) and low-temperature photoluminescence (PL). Single layers of Si0.9Ge0.1 30, 100, 1000, and 2000 nm thick on p+Si(100) waf ers were investigated to determine the effect of strain on the indirec t and direct optical transitions. The thinner two layers were pseudomo rphic and the thicker ones relaxed. The samples were examined by spect roscopic ellipsometry, which allowed the optical constants to be deter mined from the ultraviolet to near infrared (3.5-1.8 eV). Using optica l constants available from the literature for cubic Si1-xGex, the thic knesses of the alloy layers were verified. From our optical constants and the published calibration curves for normal incidence reflectivity at 633 nm and for the energy of the E1 transition (both a function of x), we found that the average germanium concentration appeared to be significantly below the nominal 10% for these samples. Phonon-resolved PL spectra were observed at 2 K for the thicker three samples with th e transition from strained to unstrained layers clearly visible in the shift of the Si1-xGex band gap as seen from the energy of the no-phon on line. Dislocation lines appeared only for the relaxed material and the no-phonon line widths were approximately 4 times smaller for the s trained Si1-xGex material.