Controllable intrinsic defect-induced electronic structure modulation in few-layer pentagonal PdPS

Palladium phosphide sulfide (PdPS), a two-dimensional (2D) semiconductor with a unique Cairo pentagonal lattice, shows great potential for optoelectronic and thermoelectric applications. However, its electronic transport behavior is strongly influenced by intrinsic defects. In this work, we systematically investigate the formation mechanisms and electronic consequences of intrinsic point defects in few-layer PdPS using first-principles calculations. We evaluate the formation energies of sulfur (S), phosphorus (P), and palladium (Pd) vacancies, as well as the interstitial Pd atoms and reveal their impacts on the electronic band structure. Unlike common 2D semiconductors like MoS2, PdPS hosts more low-energy defect configurations, which lead to bandgap narrowing, in-gap states as well as a Fermi level shift toward the conduction band. To validate the theoretical predictions, scanning tunneling microscopy measurements were performed, revealing the distinct defect morphologies and confirming the emergence of in-gap states under controlled annealing conditions. Complementary electrical transport measurements reveal a significantly reduced Schottky barrier height and significantly improved electron transport properties, attributed to the defect-induced electronic structure modulation. These results provide atomic-scale insights into the defect-driven phenomena in 2D PdPS, offering a pathway for tailoring electronic properties via defect engineering for future field-effect transistor applications.