[9p-S011-1~13] 21.1 Joint Session K "Wide bandgap oxide semiconductor materials and devices"

▲ [9p-S011-9] Thermopower modulation clarification of the operating mechanism in wide bandgap BaSnO₃−SrSnO₃ solid-solution based thin film transistors

〇(P)ANUPKUMAR VINODRAY SANCHELA¹, Mian Wei², Hai Jun Cho^1,2, Hiromichi Ohta^1,2 (1.RIES-Hokkaido Univ., 2.IST-Hokkaido Univ.)

Keywords:electric field thermopower modulation, thin film transistor, effective thickness

Transparent oxide semiconductor (TOS) with large bandgap (E_g 4 eV) based thin-film transistors (TFTs) showing both high carrier mobility and UV-visible transparency has attracted increasing attention as a promising component for the next generation optoelectronics. Among TOSs, BaSnO₃−SrSnO₃ solid-solutions (E_g = 3.5-4.2 eV) are good candidates because the single crystal shows very high mobility. However, the TFT performance has not been optimized due to the lack of fundamental knowledge especially the effective thickness (t_eff) and the carrier effective mass (m^*). Here we demonstrate that the electric field thermopower (S) modulation method address this problem by combining with the standard volume carrier concentration (n_3D) dependence of S measurements.
Figure 1a shows the sheet carrier concentration dependences of the thermopower. The degenerate/non-degenerate threshold is located at S = −244 uV K⁻¹. In the degenerate region, the slope of the S−n_2D relationship is -198 uV K⁻¹ decade⁻¹ (dotted lines), indicating parabolic E-k relationship. In order to analyze the effective thickness of the TFT channel, we calculated the S−n_3D relationship with varied carrier effective mass (m^*) from 0.1 m₀ to 1 m₀ (Fig. 1b). In the degenerate region, the calculated values well reproduce the observed values (m^* = 0.4 m₀ for x = 0, 0.2 m₀ for x = 0.5). The difference would be due to the increase of E_g and latter would be due to the enhancement of overlap population of neighboring Sn 5s orbitals.