Thermopower Modulation Clarification of the Operating Mechanism in Wide Bandgap BaSnO₃–SrSnO₃ Solid‐Solution Based Thin Film Transistors

Abstract

shows rather high carrier mobility at room temperature (≈320 cm 2 V −1 s −1 ). [3,4] The crystal structure of BaSnO 3 is cubic perovskite type, ABO 3 with space group of Pm-3m (a = 0.4116 nm), and the A-site can be fully substituted with Sr (SrSnO 3 ), though the crystal structure is orthorhombic perovskite with space group of Pbnm (a = 0.57082 nm, b = 0.57035 nm, c = 0.80659 nm). [5] The bandgap of SrSnO 3 is ≈4.1 eV [2] and the La-doped SrSnO 3 films also show high carrier mobility (40-55 cm 2 V −1 s −1 [6,7] ) at room temperature. Thus, BaSnO 3 -SrSnO 3 solid-solutions (E g = 3.1-4.1 eV) [8] are good candidates to realize large bandgap (≈4 eV) TOS-based TFTs. Very recently, a metal-semiconductor TFT operating as depletion-mode has been reported by Chaganti et al. [9] They used the La-doped SrSnO 3 film as the channel layer. However, the TFT performance of undoped BaSnO 3 -SrSnO 3 solid-solutions, which would be better to fabricate an accumulation-mode TFT, has not been reported thus far probably due to the lack of fundamental knowledge especially the effective thickness (t eff ) and the carrier effective mass (m*), which are essential information to design the TFTs.Although several researchers have reported on the m* of SrSnO 3 , the reported m* values are scattered ranging from 0.14 to 4 m 0 . In 2007, Hadjarab et al. [10] measured the magnetic susceptibility of Sr 0.98 La 0.02 SnO 3−δ ceramic and extracted m* of 4 m 0 . Moreira et al. [11,12] and Liu et al. [13] performed the band structure calculation of SrSnO 3 and BaSnO 3 , and reported much lighter m* values; SrSnO 3 : m* = 0.14-0.23 m 0 , BaSnO 3 : 0.03-0.20 m 0 . Recently, Ong et al. [14] reported that the m* of SrSnO 3 is ≈0.4 m 0 , whereas the calculated effective mass of BaSnO 3 is m* = 0.26 m 0 with the same method. Generally, the m* of n-type TOS, in which the conduction band is composed of ns orbitals, strongly depends on the overlap integral of the neighboring ns orbitals. [15] Further, the overlap integral of ns orbitals would be insensitive to the bond angle. [16] If this assumption is correct, since the interatomic distances of neighboring Sn ions in SrSnO 3 and BaSnO 3 crystals are 0.4035 and 0.4116 nm, respectively, the m* of SrSnO 3 should be lighter than that of BaSnO 3 , which is in opposite relationship with the band calculation results. [11][12][13]

Ab-Initio Study of Electronic and Structural Properties for BaSnO3 Compound Using DFT Calculations and FP-LAPW Technique in Wein2k Software

“…Shape and size are very important parameters. We use experimental values as a input, to calculate the total energy of the perovskites compound this can be measured by the use of Thus, we can calculate energy by entering the values of volume [28]. Therefore, its graph is always parabola along y-axis.…”

“…ℇn is eigen value energy [34] In the Graph shows different orbitals [28]. Valence electrons are nearly very close to the conduction's electrons, when they jump from one band to another attain some energy as photons, and hence peaks show only for the valence electrons in the DOS.…”

“…Gap. On the other hand, those energy states in which the electrons cannot be exists are called Forbidden Gaps or Electronic Band Gaps [28].…”

Electric field thermopower modulation analyses of the operation mechanism of transparent amorphous SnO2 thin-film transistor

“…Details of the electric field modulated S measurement are described elsewhere. [17][18][19][20] Figure 2(b) shows the changes in the -S as a function of the effective gate voltage (Vg−Vth). The S values were always negative, consistent with the fact that the SnO2 film is n-type semiconductor.…”

Electric Field Thermopower Modulation Analyses of the Operation Mechanism of Transparent Amorphous SnO2 Thin-Film Transistor

“…We analyzed the conduction band bending of the SnO 2 top surface by measuring the TFT characteristics in air and vacuum, and a large threshold gate voltage shift was observed; the Fermi energy in the carrier depletion region at the top surface ($2.5 nm) of the a-SnO 2 channel sensitively shifted with the changes in the gas atmosphere. The effective channel thickness (t eff ) was analyzed by the electric field thermopower (S) modulation method,, [17][18][19][20][21] and the t eff was $1.7 6 0.4 nm in air and in vacuum. The present results would provide a fundamental design concept for developing a-SnO 2 TTFT.…”