Energy Band Alignment and Electro‐Optical Behavior of Nearly Unstrained Monolayer MoS2 Heterostructures With GaN

The integration of 2D molybdenum disulfide (MoS2) with gallium nitride (GaN) enables many interesting (opto)electronic applications, such as heterojunction diodes and UV/visible photodetectors, whose performances crucially depend on the thickness uniformity, strain and doping of MoS2 films and on the energy band alignment at the interface. This work reports a multiscale electro-optical characterization of large size (∼100 µm) monolayer (1L) MoS2 flakes directly grown on n-GaN and, for comparison, on a SiO2/Si substrate by liquid-precursors-intermediated chemical vapor deposition. XPS and micro-Raman mapping revealed a superior crystalline quality, lower average strain ε ≈ −0.06% and higher n-type doping n ≈ 0.7 × 1013 cm−2 for 1L-MoS2 grown on GaN, as compared to MoS2 grown under identical conditions on the amorphous SiO2 surface. Nanoscale current-voltage mapping by C-AFM showed a significantly reduced Schottky barrier (ΦB = 0.57 ± 0.06 eV) at 1L-MoS2/GaN interface as compared to the bare GaN surface. This result, combined with a MoS2/n-GaN work function difference WMoS2-WGaN ≈ 360 meV evaluated by KPFM mapping, revealed a type-I band alignment at the heterojunction. Finally, photocurrent measurements on macroscopic Ni/n-GaN, Ni/MoS2/n-GaN and Ni/MoS2/SiO2 lateral devices under illumination with photon energies from ∼2 to ∼5 eV showed superior electro-optical performances of Ni/MoS2/n-GaN heterojunctions both in the visible and UV range.