Engineering of band gap states of amorphous SiZnSnO semiconductor as a function of Si doping concentration.

Jun Young Choi,Sangsig Kim,Sang Yeol Lee,Keun Heo,Sung Woo Hwang,Kyung-Sang Cho

doi:10.1038/srep36504

Jun Young Choi, Sangsig Kim + Show 4 more

Open Access

https://doi.org/10.1038/srep36504

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Abstract

We investigated the band gap of SiZnSnO (SZTO) with different Si contents. Band gap engineering of SZTO is explained by the evolution of the electronic structure, such as changes in the band edge states and band gap. Using ultraviolet photoelectron spectroscopy (UPS), it was verified that Si atoms can modify the band gap of SZTO thin films. Carrier generation originating from oxygen vacancies can modify the band-gap states of oxide films with the addition of Si. Since it is not easy to directly derive changes in the band gap states of amorphous oxide semiconductors, no reports of the relationship between the Fermi energy level of oxide semiconductor and the device stability of oxide thin film transistors (TFTs) have been presented. The addition of Si can reduce the total density of trap states and change the band-gap properties. When 0.5 wt% Si was used to fabricate SZTO TFTs, they showed superior stability under negative bias temperature stress. We derived the band gap and Fermi energy level directly using data from UPS, Kelvin probe, and high-resolution electron energy loss spectroscopy analyses.

Highlights

Amorphous oxide semiconductors (AOSs) have gained much attention over the past decades as candidate materials for next-generation thin film transistors (TFTs)
To investigate the effect of Si doping on the zinc-tin oxide (ZTO) semiconductor, the energy band diagrams were carefully derived by combining the results of Kelvin probe microscopy (KP), ultraviolet photoelectron spectroscopy (UPS), and high-resolution electron energy loss spectroscopy (HR-EELS) measurements
The ZTO and SZTO thin films directly deposited on the SiO2 layer on the substrate showed an amorphous phase

Summary

Introduction

Amorphous oxide semiconductors (AOSs) have gained much attention over the past decades as candidate materials for next-generation thin film transistors (TFTs). Indium free materials, like zinc-tin oxide (ZTO), have been extensively studied for the use of active channel layer of TFTs. Oxide-based multicomponent semiconductors have several advantages over conventional Si-based semiconductors, such as visible light transparency, large area deposition at low temperature, and high carrier mobility. Investigation of the basic semiconducting properties, such as the Fermi-level and energy band gap configuration, including the position of the valence band maximum (VBM) and the conduction band minimum (CBM) are key properties related to the carrier concentration and the mobility of the films for AOS TFT operation. Sub-threshold swing (V/decade) active semiconductor layers were AOS thin films and the Fermi energy level could be controlled by changing the Si doping ratio. To investigate the effect of Si doping of ZTO on the electrical characteristics of SZTO TFTs, a series of TFTs with different Si ratios were fabricated and characterized in terms of the Si doping concentration

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Results

Conclusion