Optimizing defect states in $(Bi_{0.3}Sb_{0.7})_{2}Te_{3}$ ternary topological insulators using indium doping

This study investigates the influence of indium doping on the defect states in (Bi0.3Sb0.7)2Te3 (BST) ternary topological insulators. Thin (10 nm) and thick (60 nm) films of pristine BST and indium-doped BST (In0.14(Bi0.3Sb0.7)1.86Te3) were synthesized using pulsed laser deposition. The electronic properties were characterized through low-frequency noise spectroscopy and temperature-dependent resistance (R-T) measurements. For the 10 nm films, R-T analysis revealed that indium doping shifts the thermal activation energy by approximately 100 meV. This doping also suppresses a shallow impurity band at 72 meV, a finding corroborated by 1/f noise measurements. In the 60 nm films, noise spectroscopy was used to probe deep defect states, where indium doping was found to increase the activation energy from 292.3 meV to 392 meV -- a consistent shift of 100 meV. These findings demonstrate that indium doping is an effective method for systematically modifying both shallow and deep defect states, enhancing the insulating properties and offering a mechanism to engineer the electronic behavior of topological insulators for advanced electronic applications where noise reduction is crucial.