Fermi level tuning in Sn_1-xPb_xTe/Pb heterostructure via changing interface roughness

Superconducting SnTe-type topological crystalline insulators (TCIs) are predicted to host multiple Majorana zero modes (MZMs) which can coexist in a single vortex. Fermi level (FL) close to the Dirac points of topological surface states is helpful for detecting MZMs. However, the TCI SnTe is a heavily p-type semiconductor which is very difficult to modify to n-type via doping or alloying. In this work, we fabricate the atomically flat Sn_1-xPb_xTe/Pb heterostructure by molecular beam epitaxy, and make the p-type Sn_1-xPb_xTe become n-type through changing the interface roughness. Using scanning tunnelling microscope, we find the Dirac points of Sn_1-xPb_xTe/Pb heterostructure are always above the FL due to the Fermi level pinning (FLP) induced by topological surface states at atomically flat interface. After increasing the interface roughness, the FLP effect is suppressed and then the Dirac points of p-type Sn_1-xPb_xTe can be tuned very close to or even below the FL. Our work provides a new method for tuning the FL of SnTe-type TCI which has potential application in novel topological superconductor device.