Spectroscopic ellipsometry and photoluminescence from Si1-xGex alloys grown by atmospheric-pressure chemical vapor deposition

Si(1-x)Ge(x) layers grown using atmospheric pressure chemical vapor deposition have been characterized using both room temperature spectroscopic ellipsometry and low-temperature photoluminescence (PL). Single layers of Si(0.9)Ge(0.1) 30, 100, 1000, and 2000 nm thick on p(+)Si(100) wafers were investigated to determine the effect of strain on the indirect and direct optical transitions. The thinner two layers were pseudomorphic and the thicker ones relaxed. The samples were examined by spectroscopic ellipsometry, which allowed the optical constants to be determined from the UV to NIR. From our optical constants and the published calibration curves for normal incidence reflectivity at 633 nm and for the energy of the E1 transition, we found that the average germanium concentration appeared to be significantly below the nominal 10 percent for these samples. Phonon-resolved PL spectra were observed at 2 K for the thicker three samples with the transition from strained to unstrained layers clearly visible in the shift of the Si(1-x)Ge(x) band gap as seen from the energy of the no-phonon line. Dislocation lines appeared only for the relaxed material and the no-phonon line widths were about four times smaller for the strained Si(1-x)Ge(x) material.