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Defect Characterization in SiGe/SOI Epitaxial Semiconductors by Positron Annihilation.

Ferragut R, Calloni A, Dupasquier A, Isella G - Nanoscale Res Lett (2010)

Bottom Line: The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers.In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum.After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film.

View Article: PubMed Central - HTML - PubMed

Affiliation: L-NESS, Dipartimento di Fisica, Politecnico di Milano, via Anzani 42, 22100 Como, Italy.

ABSTRACT
The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors has been demonstrated in thin multilayer structures of SiGe (50 nm) grown on UTB (ultra-thin body) SOI (silicon-on-insulator). A slow positron beam was used to probe the defect profile. The SiO(2)/Si interface in the UTB-SOI was well characterized, and a good estimation of its depth has been obtained. The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers. In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum. After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film. Chemical analysis of the SiGe layers suggests a prevalent trapping site surrounded by germanium atoms, presumably Si vacancies associated with misfit dislocations and threading dislocations in the SiGe films.

No MeSH data available.


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Ratios of the positron–electron momentum distribution at the surface of a silicon reference sample, in the silicon oxide and at the buried interface (relative to bulk Si)
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Figure 2: Ratios of the positron–electron momentum distribution at the surface of a silicon reference sample, in the silicon oxide and at the buried interface (relative to bulk Si)

Mentions: Figure 2 shows the ratio of the positron–electron annihilation peaks of the surface, the SiO2 layer, and the SiO2/Si interface relative to the bulk silicon peak. The surface and interface signals were obtained by means of a linear combination between the oxide, the interface, and a silicon bulk contributions, with the weights given by the fractions shown in Fig. 1b. Since both the positron diffusion coefficient and the lineshape parameters relative to the thermally grown oxide and to the silicon substrate are known from the literature and from calibration experiments on bulk samples [12], the interface Doppler peak shape can be extracted. The interface peak of the Doppler ratio curve of Fig. 2 is characterized by a flat region at low momentum and by a peak at ~12 mrad (12 × 10−3m0c) due to annihilation with tightly bound oxide electrons. The absence of a clear signal of an increment of annihilation with nearly free electrons (visible at momentum zero in Fig. 2) and the need of a trapping layer at the interface convey the idea that positrons do not annihilate into voids, but rather that they are strongly localized at charged centers, most probably representing electron states created by the presence of silicon dangling bonds [13,14], as already demonstrated in positron implantation experiments with SiO2/Si samples [7] and that they sense a relatively well-ordered oxide structure, typical of low quartz [15]. The same annihilation environment can be found more or less at any semiconductor surface covered with thermally grown or natural oxide, as seen in Fig. 2.


Defect Characterization in SiGe/SOI Epitaxial Semiconductors by Positron Annihilation.

Ferragut R, Calloni A, Dupasquier A, Isella G - Nanoscale Res Lett (2010)

Ratios of the positron–electron momentum distribution at the surface of a silicon reference sample, in the silicon oxide and at the buried interface (relative to bulk Si)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2991171&req=5

Figure 2: Ratios of the positron–electron momentum distribution at the surface of a silicon reference sample, in the silicon oxide and at the buried interface (relative to bulk Si)
Mentions: Figure 2 shows the ratio of the positron–electron annihilation peaks of the surface, the SiO2 layer, and the SiO2/Si interface relative to the bulk silicon peak. The surface and interface signals were obtained by means of a linear combination between the oxide, the interface, and a silicon bulk contributions, with the weights given by the fractions shown in Fig. 1b. Since both the positron diffusion coefficient and the lineshape parameters relative to the thermally grown oxide and to the silicon substrate are known from the literature and from calibration experiments on bulk samples [12], the interface Doppler peak shape can be extracted. The interface peak of the Doppler ratio curve of Fig. 2 is characterized by a flat region at low momentum and by a peak at ~12 mrad (12 × 10−3m0c) due to annihilation with tightly bound oxide electrons. The absence of a clear signal of an increment of annihilation with nearly free electrons (visible at momentum zero in Fig. 2) and the need of a trapping layer at the interface convey the idea that positrons do not annihilate into voids, but rather that they are strongly localized at charged centers, most probably representing electron states created by the presence of silicon dangling bonds [13,14], as already demonstrated in positron implantation experiments with SiO2/Si samples [7] and that they sense a relatively well-ordered oxide structure, typical of low quartz [15]. The same annihilation environment can be found more or less at any semiconductor surface covered with thermally grown or natural oxide, as seen in Fig. 2.

Bottom Line: The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers.In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum.After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film.

View Article: PubMed Central - HTML - PubMed

Affiliation: L-NESS, Dipartimento di Fisica, Politecnico di Milano, via Anzani 42, 22100 Como, Italy.

ABSTRACT
The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors has been demonstrated in thin multilayer structures of SiGe (50 nm) grown on UTB (ultra-thin body) SOI (silicon-on-insulator). A slow positron beam was used to probe the defect profile. The SiO(2)/Si interface in the UTB-SOI was well characterized, and a good estimation of its depth has been obtained. The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers. In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum. After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film. Chemical analysis of the SiGe layers suggests a prevalent trapping site surrounded by germanium atoms, presumably Si vacancies associated with misfit dislocations and threading dislocations in the SiGe films.

No MeSH data available.


Related in: MedlinePlus