Band alignment of heterojunctions formed by different polar GaN and two of two-dimensional materials: h-BN and MoSe2

To investigate the band alignment variations of heterojunctions composed of GaN materials with different polarity faces and different two-dimensional (2D) materials, two sets of heterojunctions h-BN/c-GaN, h-BN/(11-22)-GaN, h-BN/a-GaN and MoSe2/c-GaN, MoSe2/(11-22)-GaN, MoSe2/a-GaN were prepared. The valence band offsets (VBOs) of the heterojunctions were measured directly by x-ray photoelectron spectroscopy, and the conduction band offsets were then computed from the VBOs. The compounds h-BN/c-GaN, h-BN/(11-22)-GaN, and h-BN/a-GaN all classify as type-I heterojunctions, with VBOs of 0.68 eV, 1.59 eV, and 0.89 eV, respectively. The heterojunctions MoSe2/c-GaN, MoSe2/(11-22)-GaN, and MoSe2/a-GaN exhibit VBOs of 2.06 eV, 1.10 eV, and 2.74 eV, respectively. The heterojunctions MoSe2/c-GaN and MoSe2/a-GaN are type II heterojunctions, while MoSe2/(11-22)-GaN is a type I heterojunction. Concurrently, the change rule of heterojunction bands is summarized, and the influence of polarization effect on heterojunction bands is analyzed. The band position of the 2D material changes as the GaN material undergoes a transition from polar to semi-polar and then to non-polar. This change is evidenced by a decrease and subsequent increase in band position relative to the band position of the GaN material.