We fabricated Si1−xGex/Si photodetectors by using a staircase band gap Si1−xGex/Si structure. These devices exhibit a high optical response with a peak responsive wavelength at 0.96 μm and a responsivity of 27.8 A/W at −5 V bias. Excellent electrical characteristics evidenced by good diode rectification are also demonstrated. The dark current density is 0.1 pA/μm2 at −2 V bias, and the breakdown voltage is −27 V. The high response is explained as the result of a staircase band gap by theoretical analysis.

We measured at room temperature the photoluminescence spectra of the thermally oxidized Si 1ϪxϪy Ge x C y thin films which were grown on silicon substrates by plasma-enhanced chemical vapor deposition and then wet oxidized at 1100°C for 20 min. The photoluminescence band with a peak at ϳ393 nm under the exciting radiation of ϭ241 nm was observed. Possible mechanism of this photoluminescence is discussed.

The thermally oxidized Si,.-,yGeCy thin films were grown on silicon substrates by Plasma-enhanced Chemical Vapor Deposition (PECVD) and then wet oxidized at 800°C for 20 minutes. Photoluminescence spectra of the samples were measured at room temperature under 250nm excitation. Two ultraviolet photoluminescence bands with the peaks at -370nm and -396nm were observed in the oxidized samples. Possible mechanism of this photoluminescence is discussed.

Normal-incidence SiGe/Si p -i -n photodetectors with relaxed GeSi alloy layers grown on Si buffer layers at low temperature and fraction-graded Si 1Ϫx Ge x buffers were fabricated by rapid thermal process/very-low-pressure chemical-vapor deposition. The response wavelength of these detectors ranges from 0.7 to 1.55 m. The peak wavelengths are 0.98 and 1.06 m, at which the responsivities are 2.7 and 1.8 A/W ͑Ϫ2 V͒, respectively. The responsivities at 1.3 m are 0.15 and 0.07 A/W ͑Ϫ5 V͒, and the dark current densities are 0.05 and 0.03 A/mm 2 ͑Ϫ2 V͒, respectively. The influences of the Ge fraction, epilayer thickness, and bias voltage on the detectors are discussed.