Electronic structure of the PLD grown mixed phase MoS2/GaN interface and its thermal annealing effect

Abstract

We report the electronic structure of Molybdenum disulfide (MoS2) ultrathin 2D films grown by pulsed laser deposition (PLD) on top of GaN/c-Al2O3 (0001) substrates annealed up to 550 °C in an ultrahigh vacuum. Our X-ray photoemission spectroscopy (XPS) study shows that the grown films are mixed phase character with semiconducting 2H and metallic 1T phases. After ultrahigh vacuum (UHV) annealing, the 1T/2H phase ratio is significantly modified and film-substrate bonding becomes the leading factor influencing variation of mixed phase compositions. The semiconducting phase is partially transformed to metallic phase by thermal annealing; suggesting that the metallic phase observed here may indeed have more stability compared to the semiconducting phase. The notable enhancement of the 1T/2H ratio induces significant changes in Ga 3d core level spectra taken from bare GaN and MoS2/GaN sample. The impact of S and/or Mo atoms on the Ga core level spectra is further pronounced with the thermal annealing of grown films. The analysis shows that an enhancement of 1T metallic phase with thermal annealing in MoS2 layers is manifested by the occurrence of new spectral component in the Ga 3d core level spectra with the formation of Ga-S adlayer interaction through the Ga bonding in defect assisted GaN structure.