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.

💡 Research Summary

This work investigates how intentional indium (In) doping modifies the charged‑impurity landscape and consequently the surface transport properties of ternary (Bi,Sb)₂Te₃ (BST) topological insulator thin films. Using pulsed laser deposition (PLD), the authors grew 30 nm‑thick BST and In‑doped BST (IBST) layers on Si/SiO₂ substrates equipped with a back‑gate (300 nm SiO₂). Gate‑dependent resistance measurements reveal that pristine BST exhibits metallic behavior for negative gate voltages (V_g ≤ 0 V) and insulating behavior for positive V_g, with low‑temperature transport governed by Mott variable‑range hopping (R ∝ exp