Arsenene: Two-dimensional buckled and puckered honeycomb arsenic systems

C. Kamal and Motohiko Ezawa

Phys. Rev. B 91, 085423 – Published 23 February 2015

Abstract

Recently, phosphorene, a monolayer honeycomb structure of black phosphorus, was experimentally manufactured and has attracted rapidly growing interest. Motivated by phosphorene, here we investigate the stability and electronic properties of the honeycomb structure of the arsenic system based on first-principles calculations. Two types of honeycomb structures, buckled and puckered, are found to be stable. We call them arsenenes, as in the case of phosphorene. We find that both buckled and puckered arsenenes possess indirect gaps. We show that the band gap of puckered and buckled arsenenes can be tuned by applying strain. The gap closing occurs at 6% strain for puckered arsenene, where the bond angles between the nearest neighbors become nearly equal. An indirect-to-direct gap transition occurs by applying strain. Specifically, 1% strain is enough to transform puckered arsenene into a direct-gap semiconductor. We note that a bulk form of arsenic called gray arsenic exists which can be used as a precursor for buckled arsenene. Our results will pave the way for applications to light-emitting diodes and solar cells.

Received 17 November 2014
Revised 8 January 2015

DOI:https://doi.org/10.1103/PhysRevB.91.085423

Authors & Affiliations

C. Kamal^1,* and Motohiko Ezawa^2,†

¹Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India
²Department of Applied Physics, University of Tokyo, Hongo 7-3-1, Tokyo 113-8656, Japan

^*ckamal@rrcat.gov.in
^†ezawa@ap.t.u-tokyo.ac.jp

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Vol. 91, Iss. 8 — 15 February 2015

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Figure 1
Optimized geometric structures, phonon dispersion curves, electronic band structure, and density of states of puckered, planar, and buckled arsenenes. Fully optimized structure of (a) puckered (b) planar, and (c) buckled arsenene. The length of the red arrow indicates the lattice constant. Brillouin zone of (d) puckered (e) planar, and (f) buckled arsenenes. The Brillouin zone of puckered arsenene is rectangular, while those of planer and buckled arsenene are hexagonal. We mark the high symmetric points. (g) (h),(i): Phonon dispersion curves for (g) puckered (h) planar, and (i) buckled arsenenes. Puckered arsenene is globally stable since the global minimum exists at the $Γ$ point. Planar arsenene is unstable since it possesses a few modes with negative frequency. In buckled arsenene, all the modes contain positive values of frequency except the transverse acoustic mode near the $Γ$ point. Electronic band structure of (j) puckered, (k) planar, and (l) buckled arsenenes. The indirect band gap (direct band gap at $Γ$ ) is indicated by the green (blue) arrow. Puckered and buckled arsenenes are indirect semiconductors, while planar arsenene is a metal. Total and partial densities of states of (m) puckered, (n) planar, and (o) buckled arsenene. The $P$ orbitals are dominant for all structures.
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Figure 2
Effect of strain on energy, geometric structure, and band structure. (a) Variation of the total energy with strain along lattice vectors $a$ and $b$ for puckered arsenene. The total energy is parabolic, where the bottom is at $0 %$ strain. The total energy with strain along lattice vectors $a$ is higher than that along lattice vectors $b$ . (b) The intersection of two curves represents the globally optimized lattice constants $a$ and $b$ . Black circles (red squares) show the optimized lattice constant $b$ ( $a$ ) by fixing lattice constant $a$ ( $b$ ). (c) and (d) Variation of bond lengths and bond angles with strain along lattice vectors $a$ and $b$ . Around the equilibrium structure, the bond length and angle vary linearly with strain. Angles $θ_{1}$ and $θ_{2}$ become the same at $6 % (- 10 %)$ strain along lattice vector $a$ ( $b$ ), where the band gap nearly closes. See Figure 3. (e) The band gap for puckered arsenene. The band gap reaches the minimum at $6 % (- 10 %)$ strain along lattice vector $a$ ( $b$ ), while it is maximum at $- 2 % (12 %)$ strain along lattice vector $a$ ( $b$ ). The band gap is zero beyond $- 12 %$ strain along lattice vector $a$ , where the system becomes metallic. (f) The band gap for buckled arsenene. The band gap attains the maximum value at $2 %$ strain. The system becomes metallic beyond $12 %$ and $- 10 %$ strain due to the overlap between the valence and conduction bands.
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Figure 3
Variation of electronic band structures with strain along lattice vectors $a$ and $b$ . (a) The band gap nearly closes at $6 %$ strain. The system is metallic beyond $- 12 %$ strain. The indirect-to-direct gap transition occurs at $1 %$ and $- 2 %$ strain. (b) The band gap nearly closes at $- 10 %$ strain. The indirect-to-direct gap transition occurs at $2 %$ and $- 4 %$ strain. The blue circles indicate the lowest conduction-band and highest valence-band edges.
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Figure 4
Charge density distribution of the two valence (A and B) and two conduction-band (C and D) edge states, near Fermi level, for puckered arsenene. (a) Without strain. (b) With $- 4 %$ strain along $a$ . (c) With $+ 4 %$ strain along $a$ . (d) With $- 4 %$ strain along $b$ . (e) With $+ 4 %$ strain along $b$ . The red arrows indicate the minimum-energy transition between these states.
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Figure 5
Variation of electronic band structures as a function of strain for buckled arsenene. The system becomes metallic beyond $12 %$ and $- 10 %$ strain. The blue circles indicate the lowest conduction-band and highest valence-band edges
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Figure 6
Variation of electronic band structures with the transverse static electric field for buckled and puckered arsenenes. (a) Buckled arsenene. The value above the subfigure represents the strength of the transverse electric field in units of V/nm. The system becomes a direct-gap semiconductor beyond $4.2$ V/nm and then becomes a metal beyond $5.8$ V/nm due to the overlap between the valence and conduction bands. (b) The evolution of the band gap with the strength of electric field. The band gap is constant below $4.2$ V/nm, where the system is an indirect-gap semiconductor. The band gap linearly decreases between $4.2$ and $5.8$ V/nm. (c) Puckered arsenene. There is no change in the electronic structures, near the Fermi level, of puckered arsenene when it is subjected to electric field strengths up to $5.0$ V/nm. The blue circles indicate the lowest conduction-band and highest valence-band edges.
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