Thickness-Dependent Phase Stability and Electronic Properties of GaN Nanosheets and MoS₂/GaN van der Waals Heterostructures

Abstract

The formation of GaN-based heterostructures is essential for optoelectronic applications, but it is greatly limited by the traditional heteroepitaxial method due to the impact of lattice mismatch. Integrating two-dimensional layered semiconductors (e.g., MoS2) on GaN surface into van der Waals (vdW) heterostructures can effectively overcome the constraint of lattice mismatch but also create the possibility to induce novel electronic and optical properties due to size and interface effects. Here we report the thickness effect on the structural, electronic, and optical properties of GaN nanosheets and MoS2/GaN van der Waals heterostructures based on hybrid density functional theory calculations. Our results demonstrate the thickness-driven structural transitions of GaN nanosheets from the wurtzite, to the haeckelite, to the graphitic phase, which is accompanied by a direct-to-indirect band gap transition. The integration of a MoS2 monolayer on GaN nanosheets into MoS2/GaN vdW heterostructures exhibits the strong thickness dependence of the band gap, band alignment, and optical absorption coefficient. Overall, two-dimensional MoS2/GaN vdW heterostructures possess moderate band gaps (1.35–1.7 eV), type II band alignment, and large visible-light absorption coefficients, which make them potential candidates for photovoltaic and photocatalytic applications.

Absorption and emission modulation in a MoS2–GaN (0001) heterostructure by interface phonon–exciton coupling

“…Several stacking configurations were considered, as shown in the SI, but our calculations clearly favored the structure shown in Figure 1(a-b) with S and Mo atoms aligned with the topmost Ga and N, respectively. The analysis of relative band edge positions (c) indicated that in all the configurations the band gap is strongly reduced with respect to GaN, in agreement with the previous studies [13], [25]. The most stable structure reveals a band gap of predominantly of MoS2 origin, which is further confirmed by the electronic structure (d).…”

“…In order to explain the modulation of emission properties of MoS2 on GaN substrate, we consider the charge transfer across the interface, as shown in the scheme in Figure 5. As discussed in the previous paragraphs, DFT calculations confirm the type-I band alignment consistent with reported results [13], [18]. With an optical excitation at 2.33 eV, the carriers in MoS2 are excited at K-point at higher energy levels [42].…”

A two-dimensional MoS2/C3N broken-gap heterostructure, a first principles study

“…The vdW heterostructures of MoS 2 monolayer stacked on AlN (GaN) semiconductors has been well studied, 45,46 and the band alignment can be tuned by varying the thickness of GaN. The work function can be used as an intrinsic reference for the band alignment.…”

Tunable Photocatalytic Properties of Planar GaN/GeC Hetero-Bilayer: Production of H₂ Fuel

“…Among different methods of tailoring processes that are mentioned in the research community, the vdW realization of 2D planar GaN with 2D oxides and 2D TMDs become more popular. Some theoretical realizations are MoS2/GaN, phosphorene/GaN, GeC/GaN, BAs/GaN, and BP/GaN [31][32][33][34][35][36][37]. They all show stacking responsive bandgap altering nature, spatial separation of the carrier, and highphotocatalytic active sites, etc.…”