Phonon Engineering in Twinning Superlattice Nanowires

Luca, Marta De; Fasolato, Claudia; Verheijen, Marcel A.; Ren, Yizhen; Swinkels, Milo Y.; Kölling, Sebastian; Bakkers, Erik P. A. M.; Rurali, Riccardo; Cartoixà, Xavier; Zardo, Ilaria

doi:10.1021/acs.nanolett.9b01775

Cited by 38 publications

(52 citation statements)

References 49 publications

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“…properties. 44,45 Similar effects have also been reported in the less-common crystal-phase core−multishell NWs. 46,47 The vast majority of applications that can be envisaged in this context rely on impurity doping, which is the primary approach to tune the electrical conductivity of semiconductors.…”

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confidence: 68%

Doping of III–V Arsenide and Phosphide Wurtzite Semiconductors

et al. 2020

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The formation energies of n-and p-type dopants in III−V arsenide and phosphide semiconductors (GaAs, GaP, and InP) are calculated within a first-principles total energy approach.Our findings indicate thatfor all the considered systemsboth the solubility and the shallowness of the dopant level depend on the crystal phase of the host material (wurtzite or zincblende) and are the result of a complex equilibrium between local structural distortion and electronic charge reorganization. In particular, in the case of acceptors, we demonstrate that impurities are always more stable in the wurtzite lattice with an associated transition energy smaller with respect to the zincblende case. Roughly speaking, this means that it is easier to p-type dope a wurtzite crystal and the charge carrier concentration at a given temperature and doping dose is larger in the wurtzite as well. As for donors, we show that neutral chalcogen impurities have no clear preference for a specific crystal phase, while charged chalcogen impurities favor substitution in the zincblende structure with a transition energy that is smaller when compared to the wurtzite case (thus, charge carriers are more easily thermally excited to the conduction band in the zincblende phase). ■ INTRODUCTIONCrystal-phase engineering is an emerging field in nanoscience that consists of the design of materials with tailor-made properties by growing ad hoc crystal phases. The interest in this field was boosted by the enormous progresses made in recent years in the growth of semiconducting nanowires (NWs) 1,2 and, specifically, by the fact that metastable crystal phases, which in bulk can only be obtained under extreme conditions of temperature and pressure, can be stabilized at room temperature and atmospheric pressure, thanks to a tight control of growth conditions. 3 Many III−V semiconductors, such as arsenides 4−7 and phosphides, 8−11 that in bulk only exhibit the zincblende (ZB) phase, can take the wurtzite (WZ) structure when grown as NWs. Similarly, Si and Ge group-IV semiconductors that in bulk have the 3C cubic-diamond crystal structure can be synthesized in the 2H hexagonal-diamond (i.e., lonsdaleite) polytype. 12−15 The possibility of growing semiconductors in different crystal phases is very appealing, as it might enable novel applications. 16 For instance, ZB GaP has an indirect band gap and thus a limited light emission efficiency, but in WZ GaP NWs, the band gap becomes direct, resulting in a strong photoluminescence. 9 Direct-band gap emission has also been predicted and reported in hexagonal Ge and SiGe alloys, 17,18 materials that have a notoriously poor light emission in the conventional cubic polytype adopted in the bulk. Moreover, in general, different polytypes can present different electronic, 7,19−21 optical, 22−26 and phononic properties. 27−31 48 Perhaps, the most ambitious (and exciting) goal of crystal-49 phase engineering is the design of complex structures by 50 working only (or mostly) with different polytypes of the same 51 material. The co...

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confidence: 68%

Doping of III–V Arsenide and Phosphide Wurtzite Semiconductors

et al. 2020

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“…Unlike the intensive theoretical studies, the experimental reports on lattice dynamics of NWs remain scarce. Confinement of optical phonons in Si [37][38][39][40][41] and III-V [42] NWs were studied by Raman spectroscopy. Resonant and propagative coherent acoustic phonon modes were investigated by time-resolved spectroscopy with visible light [43] and x rays [44].…”

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confidence: 99%

Lattice dynamics of endotaxial silicide nanowires

et al. 2020

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Self-organized silicide nanowires are considered as building blocks of future nanoelectronics and have been intensively investigated. In nanostructures, the lattice vibrational waves (phonons) deviate drastically from those in bulk crystals, which gives rise to anomalies in thermodynamic, elastic, electronic, and magnetic properties. Hence a thorough understanding of the physical properties of these materials requires a comprehensive investigation of the lattice dynamics as a function of the nanowire size. We performed a systematic lattice dynamics study of endotaxial FeSi 2 nanowires, forming the metastable, surface-stabilized α phase, which are in-plane embedded into the Si(110) surface. The average widths of the nanowires ranged from 24 to 3 nm, and their lengths ranged from several micrometers to about 100 nm. The Fe-partial phonon density of states, obtained by nuclear inelastic scattering, exhibits a broadening of the spectral features with decreasing nanowire width. The experimental data obtained along and across the nanowires unveiled a pronounced vibrational anisotropy that originates from the specific orientation of the tetragonal α-FeSi 2 unit cell on the Si(110) surface. The results from first-principles calculations are fully consistent with the experimental observations and allow for a comprehensive understanding of the lattice dynamics of endotaxial silicide nanowires.

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“…Such homostructures (i.e., same composition, different crystal phase) have allowed to circumvent two main problems related to conventional heterojunctions formed between two different materials; namely interface mixing and lattice mismatch, leading to atomically sharp, unstrained junctions. This characteristic has opened the door to crystal-phase engineering with NWs 1,2, 3,4 .…”

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confidence: 99%