Optical and electrical evaluations of SiGe layers on insulator fabricated using Ge condensation by dry oxidation

Abstract

Photoluminescence (PL) and dual-metal-oxide-semiconductor (dual-MOS) deep level transient spectroscopy (DLTS) evaluations were performed for SiGe layers on insulator fabricated using Ge condensation by dry oxidation. Defect generation and transformation during the temperature ramp-up process were studied by PL. Band–band transition PL peaks were clearly observed for the as-grown wafers and the peak intensities decreased with an increase in the target temperature ( T t). Defect-related PL signals were observed at around 0.82, 0.88, 0.95, and 1.0 eV, which varied according to T t and the SiGe thickness. The dependence of defect-related PL on T t consists with that the defect generation of misfit-dislocation and transformation to stacking-faults with increasing T t, which was conformed by transmission electron microscopy. After Ge condensation by dry oxidation, four strained Si/SiGe on insulator (SSGOI) wafers having different Ge fractions (Ge%) and Ge condensation temperatures ( T c) were evaluated using PL and dual-MOS DLTS methods. For the sample with Ge% = 20% and T c = 1200 °C, a broad defect-related PL signal could be observed. Other SSGOI samples showed deep-level-free PL signal in the energy range from 0.77 eV to band gap, implying high wafer qualities. At mid-gap, the interface states densities ( D it) of wafers with Ge% = 15% and 20% were approximately 5 × 10 11 and 1 × 10 12 cm −2 eV −1, respectively, which were higher than that of Si/buried oxide (BOX) in a Si on insulator wafer. The high D it of SiGe/BOX was not due to interface roughness but due to the weakness of Ge–O bonds. No deep traps with concentration great than 3 × 10 11 cm −3 were detected by dual-MOS DLTS measurement in the energy range of from 0.07 to 0.24 eV above the top of valence band. Based on the PL and dual-MOS DLTS evaluations, wafer quality dependences on Ge condensation parameters were discussed. One-dimensional mappings for SiGe layer crystallinity by band–band PL intensity and D it by dual-MOS DLTS were also performed from center to edge for all the SSGOI wafers.