Large surface charge accumulation in 2D MoS2/Sb2Te3 junction and its effect on junction properties: KPFM based study

In the present study, 2D-3D MoS2/Sb2Te3 (n-p) and MoS2/Bi2Te3 (n-n) heterojunctions with varying MoS2 thicknesses have been investigated using the Kelvin Probe Force Microscopy technique. Nanoscale maps of interface measurements based on the difference of surface potential (SP) maps in surface charge and back natural modes have been carried out. The 2D-3D heterojunctions with lower MoS(2 )thickness show a large difference in SP values in the two modes, which is observed to increase with a decrease in the MoS2 thickness. In comparison, samples with larger (bulk-like) MoS(2 )thickness show negligible SP differences, indicating complete Fermi level alignment, as expected in a normal bulk junction. The difference in the SP value in two modes represents large surface charge accumulation in the 2D layer due to a relatively high value of the depletion width required for achieving equilibrium in comparison to the atomic scale thickness of 2D MoS2. In limited earlier reports, the current-voltage behavior of metal-2D MoS2 junctions is explained on the basis of the Fermi level pinning effect, which is a very generic explanation given for bulk p-n heterojunctions and may not be applicable in 2D materials. The present study shows that surface charge accumulation has a large influence on the I-V characteristic of 2D junctions, and this may be a key factor influencing the physics of the 2D interface and their potential applications. Published by AIP Publishing.