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

Abstract

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.

Theoretical research on p‐type doping two‐dimensional GaN based on first‐principles study

“…The calculation results are presented in Table 2. GaN length of pure buckled two‐dimensional GaN (1.98 Å) is higher than that of planar 2D GaN (1.85 Å), 36 the reason may be that planar sp 2 hybrid orbital becomes a tetrahedral sp 3 orbital after hydrogenation, which magnifies bond length. Under different doping situations, the GaN length is close to pure 2D GaN since GaN bond is far from doping elements.…”

Band alignment of two-dimensional semiconductors for designing heterostructures with momentum space matching

“…After the exfoliation of hexagonal boron nitride monolayers, 5,40 search for similar Group IV and III-V compound materials and designing nanoscale devices composed of their heterostructures has drawn considerable attention. [41][42][43][44][45] It is possible to separate these materials into two distinct groups depending on their stable geometries. ?…”

Lateral and Vertical Heterostructures of h-GaN/h-AlN: Electron Confinement, Band Lineup, and Quantum Structures

“…It has a slightly smaller but direct band gap. In the third one, A: (h-GaN) 4 /(h-AlN) 4 , which is constructed of slightly larger stripes relative to the formers, the band gap becomes indirect again. In this last heterostructure, the electronic states start to confine in different constituent stripes.…”