Critical Assessment of Contact Resistance and Mobility in Tin Perovskite Field-Effect Transistors

Abstract

Recent reports highlight the potential of tin-based perovskite semiconductors for high-performance p-type field-effect transistors (FETs) with mobilities exceeding 20 cm² V⁻¹ s⁻¹. However, these high mobilities—often obtained via two-probe (2P) methods on devices with small channel length-to-width ratios (L/W < 0.5) operating in the saturation regime at high drain-source currents—raise concerns about overestimation due to contact resistance and non-ideal FET characteristics. Here, gated four-point probe (4PP) FET measurements is performed on Hall bar devices (L/W = 5) of Cs_0.15FA_0.85SnI₃, obtaining a consistent mobility of 3.4 cm² V⁻¹ s⁻¹. V_G-dependent 4PP mobility is accurately extracted using the Hofstein and Heiman's MOSFET model. Upon comparing these with gated 2P measurements of narrow-channel FETs (L/W = 0.1) on the same chip, the contact resistance (R_C) is resolved. The 2P linear mobility is underestimated due to voltage drops across R_C, while the 2P saturation mobility is overestimated because of high ($\frac{\partial R_C}{\partial V_G}$) near the threshold. Contact resistance effects become more pronounced at lower temperatures. Contact-corrected 4-point-probe (4PP) mobilities are independent of bias conditions and are observed to flatten at temperatures lower than 180 K. Future reports of perovskite FET mobilities should include gated 4PP measurements and use devices with larger L/W ratios to minimize nonidealities arising from contact resistance effects.