Hexagonal AlN: Dimensional-crossover-driven band-gap transition

Bacaksız, Cihan; Şahin, Hasan; Özaydın, H. D.; Horzum, Şeyda; Senger, R. T.; Peeters, F. M.

doi:10.1103/physrevb.91.085430

Cited by 135 publications

(147 citation statements)

References 62 publications

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“…As the applied strain increases, the energy difference between two valence band edges also increases. A similar shift in VBM of hexagonal aluminium nitride (h-AlN) was reported by Bacaksiz et al [30]. The VBM of GaS consists of p z orbitals of the Ga and S atoms.…”

Section: Structural and Electronic Propertiessupporting

confidence: 48%

Mechanical properties of monolayer GaS and GaSe crystals

et al. 2016

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The mechanical properties of monolayer GaS and GaSe crystals are investigated in terms of their elastic constants: in-plane stiffness (C), Poisson ratio (ν), and ultimate strength (σ U ) by means of first-principles calculations. The calculated elastic constants are compared with those of graphene and monolayer MoS 2 . Our results indicate that monolayer GaS is a stiffer material than monolayer GaSe crystals due to the more ionic character of the Ga-S bonds than the Ga-Se bonds. Although their Poisson ratio values are very close to each other, 0.26 and 0.25 for GaS and GaSe, respectively, monolayer GaS is a stronger material than monolayer GaSe due to its slightly higher σ U value. However, GaS and GaSe crystals are found to be more ductile and flexible materials than graphene and MoS 2 . We have also analyzed the band-gap response of GaS and GaSe monolayers to biaxial tensile strain and predicted a semiconductor-metal crossover after 17% and 14% applied strain, respectively, for monolayer GaS and GaSe. In addition, we investigated how the mechanical properties are affected by charging. We found that the flexibility of single layer GaS and GaSe displays a sharp increase under 0.1e/cell charging due to the repulsive interactions between extra charges located on chalcogen atoms. These charging-controllable mechanical properties of single layers of GaS and GaSe can be of potential use for electromechanical applications.

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Section: Structural and Electronic Propertiessupporting

confidence: 48%

Mechanical properties of monolayer GaS and GaSe crystals

et al. 2016

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“…Although bulk h-AlN is a direct gap insulator, it was recently shown that its layered structure reveals an indirect gap character up to ten layers [45]. The differences in the band splittings of bulk and layered h-AlN were stressed previously, which implies that diversity in the optical spectra should also be expected.…”

Section: B Layer-dependent Optical Properties Of H-alnmentioning

confidence: 98%

“…For h-AlN, the main absorption peak of the calculated spectrum is situated around 8.6 eV, where the absorption phenomenon occurs the most intensely. The onset of interband absorption resides near 4.4 eV, which appears slightly higher than the direct band gap of 3.4 eV [45], where the difference most probably results from further band-to-band transitions with higher energy values. Another feature is the shoulder structure around both 6.8 eV and 7.3 eV.…”

Section: A Optical Properties Of Bulk Aln Crystalmentioning

confidence: 99%

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Layer- and strain-dependent optoelectronic properties of hexagonal AlN

et al. 2015

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Motivated by the recent synthesis of layered hexagonal aluminum nitride (h-AlN), we investigate its layerand strain-dependent electronic and optical properties by using first-principles methods. Monolayer h-AlN is a wide-gap semiconductor, which makes it interesting especially for usage in optoelectronic applications. The optical spectra of 1-, 2-, 3-, and 4-layered h-AlN indicate that the prominent absorption takes place outside the visible-light regime. Within the ultraviolet range, absorption intensities increase with the number of layers, approaching the bulk case. On the other hand, the applied tensile strain gradually redshifts the optical spectra. The many-body effects lead to a blueshift of the optical spectra, while exciton binding is also observed for 2D h-AlN. The possibility of tuning the optoelectronic properties via thickness and/or strain opens doors to novel technological applications of this promising material.

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“…Prediction of free-standing SL GaN and AlN in planar honeycomb structure, i.e., h-AlN and h-GaN, have initiated several theoretical studies attempting to reveal their mechan-* seymur@unam.bilkent.edu.tr † ciraci@fen.bilkent.edu.tr ical, electronic, and optical properties [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. While 3D wurtzite GaN (wz-GaN) is a direct-band-gap semiconductor and corresponds to a global minimum, SL h-GaN has relatively larger indirect fundamental band gap [21].…”

Section: Introductionmentioning

confidence: 99%

Single layers and multilayers of GaN and AlN in square-octagon structure: Stability, electronic properties, and functionalization

et al. 2017

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Further to planar single-layer hexagonal structures, GaN and AlN can also form free-standing, single-layer structures constructed from squares and octagons. We performed an extensive analysis of dynamical and thermal stability of these structures in terms of ab initio finite-temperature molecular dynamics and phonon calculations together with the analysis of Raman and infrared active modes. These single-layer square-octagon structures of GaN and AlN display directional mechanical properties and have wide, indirect fundamental band gaps, which are smaller than their hexagonal counterparts. These density functional theory band gaps, however, increase and become wider upon correction. Under uniaxial and biaxial tensile strain, the fundamental band gaps decrease and can be closed. The electronic and magnetic properties of these single-layer structures can be modified by adsorption of various adatoms, or by creating neutral cation-anion vacancies. The single-layer structures attain magnetic moment by selected adatoms and neutral vacancies. In particular, localized gap states are strongly dependent on the type of vacancy. The energetics, binding, and resulting electronic structure of bilayer, trilayer, and three-dimensional (3D) layered structures constructed by stacking the single layers are affected by vertical chemical bonds between adjacent layers. In addition to van der Waals interaction, these weak vertical bonds induce buckling in planar geometry and enhance their binding, leading to the formation of stable 3D layered structures. In this respect, these multilayers are intermediate between van der Waals solids and wurtzite crystals, offering a wide range of tunability.

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Hexagonal AlN: Dimensional-crossover-driven band-gap transition

Cited by 135 publications

References 62 publications

Mechanical properties of monolayer GaS and GaSe crystals

Mechanical properties of monolayer GaS and GaSe crystals

Layer- and strain-dependent optoelectronic properties of hexagonal AlN

Single layers and multilayers of GaN and AlN in square-octagon structure: Stability, electronic properties, and functionalization

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