Cation composition effects on electronic structures of In-Sn-Zn-O amorphous semiconductors

Abstract

Based on density-functional theory calculations, the effects of cation compositions on electronic structures of In-Sn-Zn-O amorphous semiconductors were investigated. We considered various composition ratios of In, Sn, and Zn in O stoichiometric condition, and found that the conduction band minimum (CBM) energy level decreases and the valence band tail (VBT) energy level extent increases as the sum of In and Sn ratios (RIn+RSn) increases. The CBM lowering is attributed to the increased overlap of the In-5s and Sn-5s orbitals as the RIn+RSn increases, and correspondingly the electron effective masses (me*) are found to be reduced. The VBT increase is found to be due to the increased density of the In and Sn atoms, near which the O-2p inter-site ppσ* coupling is larger than that near the Zn atoms. The acute O-(In,Sn)-O angles are suggested to be structurally important, giving the stronger O-O ppσ* coupling.

22.2: The influence of Oxygen Partial Pressure on the Performance of back‐channel‐etched a‐ZTO Thin‐Film Transistors

“…In the micro level, the spatial overlaps of 5s orbitals of Sn 4+ could not effectively form the carrier percolation paths between adjacent atoms, due to oxygen mixed into the active layer during vacuum sputtering [13]- [14]. Fig.…”

Achieving High Field-Effect Mobility Exceeding 50 cm<inline-formula> <tex-math notation="TeX">\(^{\mathrm {2}}\) </tex-math></inline-formula>/Vs in In-Zn-Sn-O Thin-Film Transistors

“…According to a recent calculation of the electronic structure, the Sn ion acts as a mobility enhancer, similar to the In ion in a-IZTO system, which can be attributed to the similar Sn 5s orbital structure to In 5s orbital [9]. Therefore, the higher In and Sn content (∼64 at.%) in IZTO film facilitates the effective intercalation of the Sn or In 5s orbital or makes the percolation path smaller, leading to high mobility of the resulting a-IZTO TFTs [9], [10]. Although the relative portion of the mobility enhancer including In and Sn ions is very high (∼64 at.%), the V TH and I OFF values of the resulting devices were not deteriorated.…”

37‐3: Late‐News Paper: Achieving High Field‐Effect Mobility Exceeding 60 cm2/Vs in IZTO Transistor via Metal‐Assisted Crystallization

“…In particular, IZTO TFTs has been identified to have a respectable high mobility without any compromise of ION/OFF ratio. It was attributed to the synergic intercalation of In 3+ and Sn 4+ 5s orbital cations, leading to the lower effective electron mass and enhanced mobility in the resulting field-effect transistors [5].…”