Characterization of spray pyrolyzed Ga2O3 thin films for thin-film transistor device applications

Jallorina, Michael Paul Aquisay and Antoniou, Giorgos and Uraoka, Yukiharu and Adamopoulos, George (2018) Characterization of spray pyrolyzed Ga2O3 thin films for thin-film transistor device applications. In: 7th International Symposium on Transparent Conductive Materials, 2018-10-14 - 2018-10-19, Chania, Crete, Greece.

Abstract

There has been a growing interest of the applications of wide bandgap semiconductors in solar cells, UV photodetectors, power devices, and backplane technology in display devices due to their unique optical and electron transport properties. Thus, wide bandgap materials such as amorphous zinc silicate (a-ZSO), indium oxide (In2O3), and indium gallium zinc oxide (IGZO) are finding their way into most display devices due to the aforementioned characteristics. Additionally, low-cost processing methods such as spray pyrolysis (SP)6 have been gaining attention due to the ability to manufacture devices with a minimal need for vacuum processes. A relatively less explored metal oxide is Ga2O3, a material with a wide (direct) bandgap in the range between 4.4 and 4.9 eV, and an electric field strength which is higher than SiC and GaN. There are only a handful of studies on the implementation Ga2O3 in TFTs regardless of the materials promising physical properties. In this regard, we present a facile method of fabricating Ga2O3 films through spray pyrolysis. The films were characterized by a wide range of techniques including UV-Vis, spectroscopic ellipsometry, FTIR, AFM, GIXRD and field effect measurements to ascertain their structural and electronic properties. Through thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), the decomposition and crystallization temperature of the GaCl3 precursor was determined and this analysis constituted the reference of the resulting films structures and device properties. Ga2O3 films were obtained by spray coating of 0.1 M solutions of GaCl3 in ethanol and methanol. The film deposition was occurred in ambient air at a substrate temperature of about 450C. Analyses revealed films of band gap of about ~4.95 consistent with the values reported for Ga2O3 films. FTIR and TGA/DSC data show the presence of amorphous and β-Ga2O3 films at temperatures <450C and >450C respectively as confirmed by GIXRD. The amorphous to β-Ga2O3 phase transition dramatically affected the performance of the Ga2O3-based TFTs where electron mobilities in excess of 20 cm2/Vs and on/off current modulation ratio on the order of 107 were recorded for TFTs implementing β-Ga2O3.