Layer- and strain-dependent optoelectronic properties of hexagonal AlN

Modarresi

Journal of Physics and Chemistry of Solids

et al. 2017

We study the electronic and optical properties of strained single-layer SnC in the density functional theory (DFT) and tightbinding models. We extract the hopping parameters tight-binding Hamiltonian for monolayer SnC by considering the DFT results as a reference point. We also examine the phonon spectra in the scheme of DFT, and analyze the bonding character by using Mulliken bond population. Moreover, we show that the band gap modulation and transition from indirect to direct band gap in the compressive strained SnC. The applied tensile strain reduces the band gap and eventually the semiconductor to semimetal transition occurs for 7.5% of tensile strain. In the framework of tight-binding model, the effect of spin-orbit coupling on energy spectrum are also discussed. We indicate that while tensile strain closes the band gap, spin-orbit gap is still present which is order of ∼ 40 meV at the Γ point. The substrate effect is modeled through a staggered sub-lattice potential in the tight-binding approximation. The optical properties of pristine and strained SnC are also examined in the DFT scheme. We present the modulation of real and imaginary parts of dielectric function under applied strain.

Section: Resultsmentioning

confidence: 99%

First principle and tight-binding study of strained SnC

Modarresi

Journal of Physics and Chemistry of Solids

et al. 2017

“…(iv) The optical-absorption onset energy when going from 3D to 2D GaN is blueshifted, where absorption for g-GaN kicks off within the visible light region or more toward the uv range, differently from 3D wz-and zb-GaN. (v) The evident lower amplitude of the absorption spectrum of g-GaN compared to wz-GaN and zb-GaN is a well-known pattern [65] due to the weaker linear optical response of a single layer of g-GaN, normal to the incident light. This is contrary to bulk wz(zb)-GaN crystals, with periodically repeating multiples of buckled GaN planes along the direction of the lattice constant c. Hence, the optical spectra of monolayer and bulk GaN show significant differences, implying that they could be used for different optoelectronic applications.…”

Section: -7mentioning

confidence: 97%

GaN: From three- to two-dimensional single-layer crystal and its multilayer van der Waals solids

et al. 2016

Self Cite

Three-dimensional (3D) GaN is a III-V compound semiconductor with potential optoelectronic applications. In this paper, starting from 3D GaN in wurtzite and zinc-blende structures, we investigated the mechanical, electronic, and optical properties of the 2D single-layer honeycomb structure of GaN (g-GaN) and its bilayer, trilayer, and multilayer van der Waals solids using density-functional theory. Based on high-temperature ab initio molecular-dynamics calculations, we first showed that g-GaN can remain stable at high temperature. Then we performed a comparative study to reveal how the physical properties vary with dimensionality. While 3D GaN is a direct-band-gap semiconductor, g-GaN in two dimensions has a relatively wider indirect band gap. Moreover, 2D g-GaN displays a higher Poisson ratio and slightly less charge transfer from cation to anion. In two dimensions, the optical-absorption spectra of 3D crystalline phases are modified dramatically, and their absorption onset energy is blueshifted. We also showed that the physical properties predicted for freestanding g-GaN are preserved when g-GaN is grown on metallic as well as semiconducting substrates. In particular, 3D layered blue phosphorus, being nearly lattice-matched to g-GaN, is found to be an excellent substrate for growing g-GaN. Bilayer, trilayer, and van der Waals crystals can be constructed by a special stacking sequence of g-GaN, and they can display electronic and optical properties that can be controlled by the number of g-GaN layers. In particular, their fundamental band gap decreases and changes from indirect to direct with an increasing number of g-GaN layers.

“…Furthermore, Bacaksiz et al 21 reported that the electronic band structure changes significantly when the number of layer increases and the structure having 10 or more layers exhibits direct bandgap as bulk form. More recently, Kecik et al 33 investigated the optical properties of mono-and few-layer h-AlN under strain. They reported that the absorption peaks stand outside the visible-light regime, on the other hand, the applied tensile strain gradually redshifts the optical spectra.…”

Section: -29mentioning

confidence: 99%

h-AlN-Mg(OH)2van der Waals bilayer heterostructure: Tuning the excitonic characteristics

et al. 2017

Self Cite

Motivated by recent studies that reported the successful synthesis of monolayer Mg(OH) 2 [Suslu et al., Sci. Rep. 6, 20525 (2016)] and hexagonal (h-)AlN [Tsipas et al., Appl. Phys. Lett. 103, 251605 (2013)], we investigate structural, electronic, and optical properties of vertically stacked h-AlN and Mg(OH) 2 , through ab initio density-functional theory (DFT), many-body quasi-particle calculations within the GW approximation, and the Bethe-Salpeter equation (BSE). It is obtained that the bilayer heterostructure prefers the AB ′ stacking having direct band gap at the Γ with Type-II band alignment in which the valance band maximum and conduction band minimum originate from different layer. Regarding the optical properties, the imaginary part of the dielectric function of the individual layers and hetero-bilayer are investigated. The hetero-bilayer possesses excitonic peaks which appear only after the construction of the hetero-bilayer. The lowest three exciton peaks are detailedly analyzed by means of band decomposed charge density and the oscillator strength. Furthermore, the wave function calculation shows that the first peak of the heterobilayer originates from spatially indirect exciton where the electron and hole localized at h-AlN and Mg(OH) 2 , respectively, which is important for the light harvesting applications.