Electron spin resonance features of the Ge Pb1 dangling bond defect in condensation-grown (100)Si/SiO_2/Si_(1-x)Ge_x/SiO_2 heterostructures

摘要

A multi-frequency electron spin resonance (ESR) study has been carried out the Ge P_(b1) dangling bond (DB)-type interface defect in SiO_2/Si_(1-x)Ge_x/SiO_2 heterostructures of different Ge fraction manufactured by the condensation technique. The notable absence of Si Pb-type centers enables unobscured spectral analysis as function of magnetic field angle, reassured by coinciding multi-frequency ESR data. The center features monoclinic-I (C_(2v)) symmetry with principal g values g_1 = 2.0338 ± 0.0003, g_2 = 2.0386 ± 0.0006, g_3 = 2.0054, with the lowest value, g_3, axis 24 ± 2° off a (111) direction towards the [100] interface normal n. The defect appearance shows a systematic variation as function of x, reaching maximum densities of ～6.8 × 10~(12)cm~(-2) per Si/SiO_2 interface for x ～ 0.7, to disappear for x outside the ]0.45-0.87[ range. The ESR signal width is dominated by inhomogeneous broadening arising from strain-induced Gaussian spread in g, resulting in frequency (v)-dependent peak-to-peak broadening of △B_(pp)~(SB)/v = 0.62 G/GHz and 1.13 G/GHz for the applied magnetic field B//g_3 principal axis and B/, respectively. Compared to the familiar Si Pb-type interface defects in (100)Si/SiO_2, the enhanced (v-dependent broadening scales with the spin-orbit coupling constant ratio λ(Ge)/λ(Si). The natural inhomogeneous broadening due to unresolved ~(73)Ge hyperfine interaction is found to be below ～1.56G, the inferred residual (ν→0) width. The core of the defect, previously depicted as a Ge P_(b1)-type center, concerns an asymmetrically back bonded trivalent Ge atom where the total of all data would suggest a back bond arrangement involving two Ge and one Si atoms and/or a strained bond. Initial studies show the defect to exhibit reversal hydrogen passivation/depassivation kinetics, where defects can be substantially, yet only partially, ESR-inactivated by heating in H_2. The properties and nature of the center are discussed within the context of the their inherent incorporation as interface mismatch centers, where assessing the defect's nature and modalities of occurrence may provide a link to unraveling the role of point defects in adapting interfacial mismatch.