Bias Polarity Switching (BiPS): A Transient Method for Probing Interfacial Carrier Dynamics

Interfaces and contacts critically influence the performance and stability of semiconductor devices, yet direct experimental access to charge accumulation and release processes near biased interfaces remains limited. Here, we introduce the Bias Polarity Switching (BiPS) technique as a transient method for probing carrier dynamics in the sub-/micrometer-scale near-interface region under realistic operating conditions. We show that BiPS enables distinction between free- and trapped-carrier contributions to the transient response, allowing extraction of carrier mobility, characteristic trapping and detrapping times, and an effective interfacial extraction rate. Applied to representative single-crystal semiconductor systems with different contact configurations, including melt-grown CsPbBr₃ (Cr/Cr) and solution-grown MAPbBr₃ (Cr, SnO₂/Cr), BiPS reveals interfacial barriers that drive carrier accumulation and defect filling. CsPbBr₃ exhibits long-lived space charge densities in the order of ∼3 × 10¹¹ cm^-3. Analysis of the BiPS transients yields trapping times of 1-100 µs, detrapping times of 20 µs-3 ms, and activation energies of 280-450 meV for interfacial defect states. Finally, a proof-of-feasibility experiment on CdZnTe demonstrates the feasibility of extending BiPS beyond perovskite materials.