P. Somers

University of Leuven, Louvain, Flanders, Belgium

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Publications (15)29.37 Total impact

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    ABSTRACT: The multi-frequency electron spin resonance (ESR) study of the GePb1 Ge dangling bond (DB) interface defect, appearing identically at both SiO2/GexSi1–x interfaces in condensation-grown SiO2/GexSi1–x/SiO2/(1 0 0)Si heterostructures (0.28 ≤ x ≤ 0.93), shows that the ESR signal width is dominated by inhomogeneous broadening due to a strain-induced spread in g. For the x = 0.73 case, this results in a frequency (ν)-dependent peak-to-peak broadening of ΔBppSB/ν = 0.62 G/GHz for the applied magnetic field B along the g3 principal axis Ge DB direction. Compared to the familiar Si Pb-type interface defects in (1 0 0)Si/SiO2, the enhanced ν-dependent broadening scales with the spin–orbit coupling constant ratio λ(Ge)/λ(Si). The natural inhomogeneous broadening due to unresolved 73Ge hyperfine interaction is found to be below ~1.56 G. While the results adduce quantitative support for the assignment of GePb1 as a Ge DB-type interface center, it is concluded that the GeSi/SiO2 interface uniformity is of good level.
    Semiconductor Science and Technology 11/2012; 28(1):015003. · 1.92 Impact Factor
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    ABSTRACT: A multi-frequency electron spin resonance (ESR) study has been carried out the Ge Pb1 dangling bond (DB)-type interface defect in SiO2/GexSi1−x/SiO2/(100)Si 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 (C2v) symmetry with principal g values g1 = 2.0338 ± 0.0003, g2 = 2.0386 ± 0.0006, g3 = 2.0054, with the lowest value, g3, 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 × 1012 cm−2 per Si/SiO2 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 (ν)-dependent peak-to-peak broadening of ΔBppSB/ν = 0.62 G/GHz and 1.13 G/GHz for the applied magnetic field B//g3 principal axis and B//n, respectively. Compared to the familiar Si Pb-type interface defects in (100)Si/SiO2, the enhanced ν-dependent broadening scales with the spin-orbit coupling constant ratio λ(Ge)/λ(Si). The natural inhomogeneous broadening due to unresolved 73Ge hyperfine interaction is found to be below ∼1.56 G, the inferred residual (ν→0) width. The core of the defect, previously depicted as a Ge Pb1-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 H2. 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.
    Journal of Applied Physics 10/2012; 112(7). · 2.21 Impact Factor
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    ABSTRACT: An electron spin resonance study has been carried out on heteroepitaxial Si/insulator structures obtained through growth of epi- Lu 2 O 3 films on (111)Si ( ∼4.5 % mismatch) by molecular-beam epitaxy, with special attention to the inherent quality as well as the thermal stability of interfaces, monitored through occurring paramagnetic point defects. This indicates the presence, in the as-grown state, of P b defects (∼5×10<sup>11</sup>  cm <sup>-2</sup>) with the unpaired sp<sup>3</sup> Si dangling bond along the [111] interface normal, the archetypical defect (trap) of the standard thermal (111) Si / SiO 2 interface, directly revealing, and identified as the result of, imperfect epitaxy. The occurrence of P b defects, a major system of electrically detrimental interface traps, is ascribed to lattice mismatch with related introduction of misfit dislocations. This interface nature appears to persist for annealing in vacuum up to a temperature T an ∼420 ° C . Yet, in the range T an ∼420–550 ° C , the interface starts to “degrade” to standard Si / SiO 2 properties, as indicated by the gradually increasing P b density and attendant appearance of the EX center, an SiO 2 -associated defect. At T an ∼700&#x20- - 09;° C , [ P b ] has increased to about 1.3 times the value for standard thermal (111) Si / SiO 2 , to remain constant up to T an ∼1000 ° C , indicative of an unaltered interface structure. Annealing at T an >1000 ° C results in disintegration altogether of the Si / SiO 2 -type interface. Passivation anneal in H 2 (405 ° C ) alarmingly fails to deactivate the P b system to the device grade (sub) 10<sup>10</sup>  cm <sup>-2</sup>  eV <sup>-1</sup> level, which would disfavor c-Lu 2 O 3 as a suitable future high- κ replacement for the a-SiO 2 gate dielectric. Comparison of the thermal stability of the c-Lu 2 O 3 /(111) Si interface with that of molecular-beam deposited amorphous- Lu 2 O 3 /(100) Si shows the former to be superior, yet unlikely to meet technological thermal budget requirements. No Lu 2 O 3 -specific point defects could be observed.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
  • Microelectronic Engineering 07/2009; 86(7-9):1621-1625. · 1.22 Impact Factor
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    ABSTRACT: Multifrequency electron-spin-resonance (ESR) study has revealed a nontrigonal Ge dangling bond (DB)-type interface defect in SiO2/(100)GexSi1−x/SiO2/Si heterostructures grown by the condensation method. The center, exhibiting monoclinic-I (C2v) symmetry, with principal g values g1=2.0338±0.0003, g2=2.038 6±0.000 6, and g3=2.005 4 and lowest g value (DB) direction 24±2° off a ⟨111⟩ direction toward the [100] interface normal, is observed in maximum densities for x∼0.7, the signal disappearing for x≤0.45 and x≥0.93. Neither Si Pb type nor trigonal Ge dangling bond defects is observed, enabling unobscured spectral analysis. Based on its ESR parameters, including g matrix and symmetry, it is suggested to concern a Ge Pb1-type center, that is, not a trigonal basic Ge Pb(0)-type center (Ge3≡Ge•), thus exposing a unique interface mismatch healing as function of substrate Ge fraction. Its properties are discussed within the context of the thus far elusive role of interfacial Ge DB defects in Ge insulator structures, encompassing theoretical inferences.
    Phys. Rev. B. 04/2009; 79(19).
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    ABSTRACT: Using electron spin resonance (ESR), we report on the observation of a first Ge dangling bond (DB)-type interface defect in the SiO(2)/(100)Ge(x)Si(1-x)/SiO(2)/(100)Si heterostructure manufactured by the condensation technique. The center, exhibiting 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 is observed in maximum densities of ∼6.8 × 10(12) cm(-2) of the Ge(x)Si(1-x)/SiO(2) interface for x∼0.7, the signal disappearing for x outside the 0.45-0.93 range. The notable absence of interfering Si P(b)-type centers enables unequivocal spectral analysis. Collectively, the combination of all data leads to depicting the defect as a Ge P(b 1)-type center, i.e. not a trigonal basic Ge P(b(0))-type center ([Formula: see text]). Understanding the modalities of the defect's occurrence may provide an insight into the thus far elusive role of Ge DB defects at Ge/insulator interfaces, and widen our understanding of interfacial DB centers in general.
    Journal of Physics Condensed Matter 03/2009; 21(12):122201. · 2.22 Impact Factor
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    ABSTRACT: Using electron spin resonance (ESR), we report on the observation of a first Ge dangling bond (DB)-type interface defect in the SiO2/(100)GexSi1−x/SiO2/(100)Si heterostructure manufactured by the condensation technique. The center, exhibiting monoclinic-I (C2v) symmetry with principal g values g1 = 2.0338 ± 0.0003, g2 = 2.0386 ± 0.0006, g3 = 2.0054 is observed in maximum densities of ~6.8 × 1012 cm−2 of the GexSi1−x/SiO2 interface for x~0.7, the signal disappearing for x outside the 0.45–0.93 range. The notable absence of interfering Si Pb-type centers enables unequivocal spectral analysis. Collectively, the combination of all data leads to depicting the defect as a Ge Pb 1-type center, i.e. not a trigonal basic Ge Pb(0)-type center (). Understanding the modalities of the defect's occurrence may provide an insight into the thus far elusive role of Ge DB defects at Ge/insulator interfaces, and widen our understanding of interfacial DB centers in general.
    Journal of Physics Condensed Matter 02/2009; 21(12):122201. · 2.22 Impact Factor
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    ABSTRACT: Multifrequency electron-spin-resonance (ESR) study has revealed a nontrigonal Ge dangling bond (DB)-type interface defect in SiO2/(100)GexSi1-x/SiO2/Si heterostructures grown by the condensation method. The center, exhibiting monoclinic-I (C2v) symmetry, with principal g values g1=2.0338±0.0003 , g2=2.0386±0.0006 , and g3=2.0054 and lowest g value (DB) direction 24±2° off a direction toward the [100] interface normal, is observed in maximum densities for xtilde 0.7 , the signal disappearing for x=0.93 . Neither SiPb type nor trigonal Ge dangling bond defects is observed, enabling unobscured spectral analysis. Based on its ESR parameters, including g matrix and symmetry, it is suggested to concern a GePb1 -type center, that is, not a trigonal basic GePb(0) -type center (Ge3≡Ge•) , thus exposing a unique interface mismatch healing as function of substrate Ge fraction. Its properties are discussed within the context of the thus far elusive role of interfacial Ge DB defects in Ge insulator structures, encompassing theoretical inferences.
    Physical review. B, Condensed matter 01/2009; 79(19). · 3.77 Impact Factor
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    ABSTRACT: The work addresses the occurrence of Ge dangling bond type point defects at GexSi1−x/insulator interfaces as evidenced by conventional electron spin resonance (ESR) spectroscopy. Using multifrequency ESR, we report on the observation and characterization of a first nontrigonal Ge dangling bond (DB)-type interface defect in SiO2/(100)GexSi1−x/SiO2/(100)Si heterostructures (0.27⩽x⩽0.93) manufactured by the condensation technique, a selective oxidation method enabling Ge enrichment of a buried epitaxial Si-rich SiGe layer. The center, exhibiting monoclinic-I (C2v) symmetry is observed in highest densities of ∼7×1012cm−2 of GexSi1−x/SiO2 interface for x∼0.7, to disappear for x outside the ]0.45–0.87[ interval, with remarkably no copresence of Si Pb-type centers. Neither are trigonal Ge DB centers observed, enabling unequivocal spectral analysis. Initial study of the defect passivation under annealing in molecular H2 has been carried out. On the basis of all data the defect is depicted as a Ge Pb1-type center, i.e., distinct from a trigonal basic Ge Pb(0)-type center (Ge3Ge). The modalities of the defect’s occurrence as unique interface mismatch healing defect is discussed, which may widen our understanding of interfacial DB centers in general.
    Microelectronic Engineering - MICROELECTRON ENG. 01/2009; 86(7):1621-1625.
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    ABSTRACT: Electron spin resonance study on heteroepitaxial Si/insulator structures obtained through the growth of epi- Lu <sub>2</sub> O <sub>3</sub> films on (111)Si ( ∼4.5 % mismatched) by reactive molecular beam epitaxy indicates the presence in the as-grown state of interfacial P<sub>b</sub> defects (∼5×10<sup>11</sup> cm <sup>-2</sup>) with an unpaired sp<sup>3</sup> Si dangling bond (DB) along the [111] sample normal, prototypical of the standard thermal (111) Si / SiO <sub>2</sub> interface. The defects, with density remaining unchanged to anneal in vacuum up to temperatures of T<sub> an </sub>∼420 ° C , directly reveal the nonperfect pseudoepitaxial nature of the interface, laid down in electrically detrimental interface traps. These are suggested to be interfacial Si DBs related to Si misfit dislocations. Alarmingly, defect passivation by standard anneal treatments in H <sub>2</sub> fall short. For higher T<sub> an </sub> , the interface deteriorates to “standard” Si / SiO <sub>2</sub> properties, with an attendant appearance of EX centers indicating SiO <sub>2</sub> growth. Above T<sub> an </sub>∼1000 ° C , the interface disintegrates altogether.
    Applied Physics Letters 10/2008; · 3.79 Impact Factor
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    ABSTRACT: A comparative electron spin resonance study is reported on (100)Si/SiO2 entities, grown by thermal oxidation of biaxial tensile strained (100)Si (sSi) layers, epitaxially grown on a strain relaxed Si0.8Ge0.2 buffer layer, and standard (100)Si. In the as-oxidized state a significant decrease ( ∼ 50%) of inherently incorporated interface defects, Pb0 and Pb1, is observed, i.e., the sSi/SiO2 interface is found to be inherently significantly improved in terms of electrically detrimental interface traps (Pb0). After vacuum-ultraviolet irradiation two more SiO2-associated defects appear, namely Eγ′ (generic entity O3 ≡ Si·) and EX. Interestingly, a decrease ( ∼ 50%) of Eγ′ defect density is observed compared to standard Si/SiO2. This reduction in inherent electrically active interface (Pb0) and near-interface (Eγ′) traps would establish sSi/SiO2 as a superior device structure for all electrical properties where (near)-interfacial traps play a detrimental role. For one, the reduction of detrimental (near)-interface defects may be an additional reason for the commonly reported mobility enhancement in sSi/SiO2 based metal–oxide–semiconductor structures over standard Si/SiO2 ones, and at the same time account for the reported reduction of 1/f noise in the former structures. The data also confirm the generally accepted notion that Pb-type defects are mismatch induced defects.
    Journal of Applied Physics 02/2008; 103(3):033703-033703-9. · 2.21 Impact Factor
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    ABSTRACT: Electron spin resonance studies are reported on (1 0 0)Si/SiO2 entities grown by thermal oxidation of biaxial tensile strained-(1 0 0)Si layers epitaxially grown on relaxed virtual substrates, with main focus on Pb-type interface defects, in particularly the electrically detrimental Pb0 variant. In the as-grown state a significant decrease (>50%) in interface defect density compared to the standard (1 0 0)Si/SiO2 interface was observed. As compared to the latter, this inherent decrease in electrically active interface trap density establishes strained Si/SiO2 as a superior device entity for all electrical properties in which (near) interface traps may play a detrimental role. For one, it may be an additional reason for the commonly reported mobility enhancement in strained silicon inversion layers and the reduction in 1/f noise. The data also confirm the admitted relationship between inherent incorporation of the Pb related interface defects and the Si/SiO2 interface mismatch.
    Materials Science and Engineering: B. 12/2006; 135(3):195–198.
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    ABSTRACT: An electron spin resonance analysis has been carried out of the intrinsic point defects in (100)Si/SiO2 entities thermally grown at 800 °C on biaxial tensile strained Si (s-Si). As compared to coprocessed standard (100)Si/SiO2, a significant reduction (>50%) is observed in the inherent density of the trivalent Pb-type interface defects (Pb0,Pb1). With the Pb0’s established as detrimental fast interface traps, this result may adduce one more reason for the observed enhancement of device channel carrier mobility with increasing Si substrate tensile strain as well as reduction in 1/f noise. The s-Si/SiO2 interface exhibits a generally superior device grade quality.
    Applied Physics Letters 10/2006; 89(15):152103-152103-3. · 3.79 Impact Factor
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    ABSTRACT: Energy barriers for electrons at interfaces of several low-permittivity insulators with metals (Ta, TaNx, TiNx, Au, and Al) are characterized using internal photoemission spectroscopy. In sharp contrast to thermal SiO2, the barriers show little sensitivity to the Fermi energy of the metal, suggesting that the uppermost occupied electron revels at the interface are states localized in the near-interfacial insulator layer. Moreover, despite large differences in the defect spectrum of the studied low-kappa materials as revealed by electron spin resonance, all the measured energy barriers are found to be close to 4.5 eV. The latter indicates an extrinsic nature of the corresponding common electron state, which is tentatively ascribed to traces of moisture at the interface.
    Applied Physics Letters 01/2006; 89. · 3.79 Impact Factor
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    ABSTRACT: Electron spin resonance (ESR) spectroscopy has become indispensable when it comes to the characterization on atomic-scale of structural, and correlated, electrical properties of actual semiconductor/insulator heterostructures. Through probing of paramagnetic point defects such as the Pb-type defects, E', and EX as a function of VUV irradiation and post deposition heat treatment, basic information as to the nature, quality, and thermal stability of the interface and interfacial regions can be established. This is illustrated by some specific examples of ESR analysis on contemporary Si/insulator structures promising for future developments in integrated circuits. First the impact of strain on the Si/SiO2 entity will be discussed. Through ESR analysis of thermally oxidized (111)Si substrates mechanically stressed in situ during oxidation, and tensile strained (100)sSi/SiO2 structures, it will be pointed out that in-plane tensile stress in Si can significantly improve the interface quality. Next, ESR results for stacks of (100)Si/SiOx/HfO2 and (100)Si/LaAlO3 are presented, revealing the potential to attain a high quality Si/SiO2 interface for the former and an abrupt, thermally stable interface for the latter.
    MRS Proceedings. 12/2005; 984.