Band Meandering due to Charged Impurity Effects and Carrier Transport in Ternary Topological Insulators

Controlling charged impurity disorder is a critical challenge for realizing the promise of topological insulator (TI) surfaces in devices. While doping is often used to tune the chemical potential, its impact on the fundamental disorder landscape remains poorly understood. Here, we investigate this effect in ternary (Bi,Sb)$_2$Te$_3$ (BST) thin films and their indium-doped (IBST) counterparts. Gate-dependent transport reveals that indium doping increases charged impurity density by an order of magnitude, which in turn reduces the characteristic size of disorder-induced charge puddles from $\sim$91 nm to $\sim$38 nm. This amplified disorder enhances Coulomb scattering and suppresses field-effect mobility, directly demonstrating how doping-induced compensation degrades surface transport. Our work establishes doping as a powerful method to probe the limits of topological protection and underscores that defect suppression, not just compensation, is essential for developing high-performance TI devices.