Energy Band Alignment and Electro‐Optical Behavior of Nearly Unstrained Monolayer MoS ₂ Heterostructures With GaN

ABSTRACT The integration of 2D molybdenum disulfide (MoS ₂ ) 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 MoS ₂ 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) MoS ₂ flakes directly grown on n‐GaN and, for comparison, on a SiO ₂ /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 × 10 ¹³ cm ⁻² for 1L‐MoS ₂ grown on GaN, as compared to MoS ₂ grown under identical conditions on the amorphous SiO ₂ surface. Nanoscale current‐voltage mapping by C‐AFM showed a significantly reduced Schottky barrier (Φ _B = 0.57 ± 0.06 eV) at 1L‐MoS ₂ /GaN interface as compared to the bare GaN surface. This result, combined with a MoS ₂ /n‐GaN work function difference W _MoS2 ‐W _GaN ≈ 360 meV evaluated by KPFM mapping, revealed a type‐I band alignment at the heterojunction. Finally, photocurrent measurements on macroscopic Ni/n‐GaN, Ni/MoS ₂ /n‐GaN and Ni/MoS ₂ /SiO ₂ lateral devices under illumination with photon energies from ∼2 to ∼5 eV showed superior electro‐optical performances of Ni/MoS ₂ /n‐GaN heterojunctions both in the visible and UV range.