Atomic resolution interface structure and vertical current injection in highly uniform MoS2 heterojunctions with bulk GaN

The integration of two-dimensional $MoS_{2}$ with $GaN$ recently attracted significant interest for future electronic/optoelectronic applications. However, the reported studies have been mainly carried out using heteroepitaxial templates on sapphire substrates, whereas growth low-dislocation-density bulk GaN can be strategic realization truly vertical devices. In this paper, we report ultrathin films, mostly composed by single-layers ($1L$), onto homoepitaxial $n-GaN$ $n^{+}$ substrates sulfurization a pre-deposited $MoO_{x}$ film. Highly uniform and conformal coverage surface was demonstrated atomic force microscopy, while very low tensile strain (0.05%) $p^{+}$-type doping ($4.5 \times 10^{12} cm^{-2}$) $1L-MoS_{2}$ evaluated Raman mapping. Atomic resolution structural compositional analyses aberration-corrected electron microscopy revealed nearly-ideal van der Waals interface between $Ga$-terminated crystal, where only topmost $Ga$ atoms are affected oxidation. Furthermore, relevant lattice parameters $MoS_{2}/GaN$ heterojunction, such as gap, were measured high precision. Finally, current injection across 2D/3D heterojunction has investigated nanoscale current-voltage performed conductive showing rectifying behavior an average turn-on voltage $V_{on}=1.7 V$ under forward bias, consistent expected band alignment at $p^{+}$ doped $n-GaN$.