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The formation and annihilation of hydrogen (H)-related complexes were investigated in boron (B)- or phosphorus (P)-doped Si treated with high concentration of atomic H. The passivation and reactivation process of dopant carriers were significantly different between the p-type and n-type specimens. The differences are explained by the stable sites of the H atoms in the p-type and n-type specimens and, in turn, by the formation of H-related defects: i.e., H multiple trapping centers are formed by bond-breaking due to H atoms only in p-type B-doped Si. The formation of such defects retards the reactivation of B dopants by annealing.

Hydrogen passivation of phosphorus (P) donors and defects in P-doped silicon nanowires (SiNWs) were investigated by electron spin resonance (ESR) at 4.2 K. P doping was performed during the synthesis of SiNWs by laser ablation. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by detection of an ESR signal with a g-value of 1.998, which corresponds to conduction electrons in crystalline Si. ESR signals related to defects in surface oxide layer and at interface between surface oxide and crystalline Si core were observed. These P donors and the defects were partially passivated by hydrogen and oxygen atoms as seen in bulk Si.

The formation of hydrogen (H)-related complexes was investigated in boron (B)-doped Si treated with high concentration of H. The isotope shifts of H-related Raman peaks by replacement of H to deuterium and 10B to 11B clearly showed the formation of the B–H complexes in which H directly bonds to B in Si. The results of the resistivity measurements suggested that the B acceptors are passivated via the formation of the B–H complexes, as well as the well-known passivation center in B-doped Si, namely, H–B passivation center.

The phonon confinement effect was investigated by Raman measurements for Si nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) catalyst and for SiNWs thermally oxidized at 700–1000 °C. The Si optical phonon peak for SiNWs, unlike that for bulk Si, showed a downshift and an asymmetric broadening. Thermal oxidation caused a further downshift and broadening. These phenomena can be explained by the phonon confinement effect due to the decrease in the diameter of the Si core of the SiNWs. It was additionally found that excess oxidation caused an upshift of the optical phonon peak due to compressive stress.

Recent experiments have shown that Si nanostructures can be formed in a matrix Of SiO2 by laser-pulse irradiation, with appealing applications in nanotechnology. We hereby present first principles simulations that provide a microscopic insight into the underlying mechanism, showing how electron excitations weaken Si-O bonds in SiO2, dislodging O atoms and allowing the formation of stable Si-Si structures below the melting temperature. (c) 2006 Elsevier B.V. All rights reserved.

We measured real-time spectra of light transmitted through SiO2 specimens during irradiation of amplified ultrashort laser. The real-time spectra exhibit a peak at around 400 nm. The observation and identification of defects were performed by measurements of electron spin resonance (ESR). Both dependences of the peak at around 400 nm on irradiation time and laser power are in good agreement with those of the ESR signal intensity of positively charged oxygen vacancies (E′ center: O3≡Si·). This strong correlation shows that self-trapped excitons are created followed by the formation of the E′ center and finally that of ESR inactive centers, namely, oxygen-deficiency centers (ODCs: O3≡Si-Si≡O3 or O3≡Si:).

We report a systematic investigation on the Fermi-level dependence of the formation of two different types of hydrogen molecules in silicon. Hydrogen molecule at the tetrahedral (T) site (H 2 (T)) is formed only in heavily doped n-type below 200°C, but is observed both in the n- and p-type above 200°C. The temperature dependence is due to the increase of the thermally activated carrier concentration. The possible precursors of the H 2 (T) are H + (BC) and H 0 (BC) in the p-type, and H − (T) and H 0 in the n-type. The Fermi level dependence of the formation of the hydrogen molecule trapped in platelets (H 2 (p)) above 250°C is very different from that below 250°C. The result suggests that platelets are formed from hydrogen-complexes other than the H 2 * above 250°C.

Wehaveinvestigatedthethermalbehaviorofhydrogenmoleculestrappedbymultivacanciesincrystallinesiliconbyperformingthermalannealing.ThehydrogenmoleculeshadtwoRamancomponentswithdifferentannealingstages.Theiractivationenergiesforannihilationwere0.7 0.3and0.5 0.2eVforthemaincomponentandtheshoulder,respectively.Theformerwasattributedtothepotentialbarrierforahydrogenmoleculetoescapefromamultivacancytrap,andthelattertomovefromametastablesitearoundthemultivacancytraptothemoststablesite.Annealingat6108CsuggestedthatrelativelylargemultivacanciessuchasV 6 andV 10 arepossibletrappingcentersofthehydrogenmolecules.# 2001ElsevierScienceB.V.Allrightsreserved. PACS: 61.72.JiKeywords: Hydrogenmolecule;Multivacancy;Annealingbehavior;Activationenergy 1. IntroductionHydrogenisanimportantimpurityinsemicon-ductorsbecauseofitsabilitytochangeelectricalpropertiesofhostmaterialsdrastically[1].Theo-retical calculations predicted that a hydrogenmoleculeisoneofthefavorableconfigurationsincrystalline silicon. Three different configurationsof hydrogen molecules have been found experi-mentally by means of vibrational spectroscopysuchasRamanscatteringandinfraredabsorption.Murakamietal.revealedtheexistenceofhydro-genmoleculesincrystallinesiliconin1996.TheyobserveditsvibrationalRamanlineat4158cm

The Raman line of a new hydrogen molecule at approximately 3820 cm −1 has been observed for the first time in silicon after Si + ion implantation with proper doses, followed by hydrogen atom treatment. The assignment was confirmed by isotope shifts to 2770 cm −1 for D 2 molecule and to 3353 cm −1 for HD molecule. Both the ion-dose dependence and hydrogenation-temperature dependence of the Raman intensity of the H 2 molecules correlate with those of the intensity of peaks of Si–H stretching observed at 1957±1.8 cm −1 and at approximately 2185 and 2210 cm −1 . We propose a model where the hydrogen molecule corresponding to the 3820 cm −1 vibrational line is trapped in or adjacent to small H-terminated multivacancies.

We report a Raman study on the hydrogenation–temperature dependence on the formation of hydrogen molecules in crystalline silicon. The 3601 cm −1 vibrational line for H 2 , which has been attributed to hydrogen molecule in T d site, is observed in p-type as well as in n-type crystalline silicon. This H 2 molecule exhibits significantly different temperature dependence in n- and p-type Si. It is suggested from the hydrogenation–temperature dependence that the charge states and the sites of atomic hydrogen affect the formation of this type of H 2 . From the experiments using H+D atom treatments, there may be a significant isotope effect on the formation of the H 2 molecule.