Oxide semiconductors have attracted significant attention in the
field of thin film transistors(TFTs) because of their high level of
carrier mobility compared to conventional amorphous silicon. The
excellent mobility of thin film transistors based on ...
Oxide semiconductors have attracted significant attention in the
field of thin film transistors(TFTs) because of their high level of
carrier mobility compared to conventional amorphous silicon. The
excellent mobility of thin film transistors based on oxide
semiconductors has enabled the development of high-resolution,
large-area displays and portable small-sized tablets. In the case of
ZTO, Zn and Sn provide excellent electrical properties, but there are
limitations in controlling the carrier concentration using only these two
elements. As the standard electrode potential(SEP) of lithium is –3.04
V, it can effectively control the defects such as the oxygen vacancy
and lithium increases the electron concentration by an interstitial
bonding which acts as a donor level in ZnO matrix. In this study, the
electrical properties and environmental stability were improved by
lithium doping on ZTO and the saturation mobility was increased by
the neutron irradiation on lithium doped ZTO.
The Zn:Sn ratio and concentration of Li-ZTO solutions were fixed
1:2 and 0.5 M respectively, and Li content was varied by 0, 3, 7 and
15 at.%. The thin films were deposited on SiO2(100 nm)/Si p++
substrate by using the spin coating method and were synthesized
through drying and heat treatment processes. In order to fabricate
TFTs, 100 nm thickness Al was deposited by thermal evaporator. The
Li 3 at.%-ZTO film was used as a neutron irradiation sample and the
fast neutron generated by 30 MeV proton irradiation on a Be target
was used. The irradiation dose was varied by changing irradiation
time from 10 to 2000 sec.
As the result of Li-ZTO TFT characteristic according to the
lithium content, the highest saturation mobility was exhibited at Li 3
at.% addition. In order to confirm the reason of increasing saturation
mobility, O 1s and Sn 3d spectra of XPS was analyzed. As increasing
lithium content, the electron concentration was decreased because
oxygen vacancy was decreased and SnO bonding was increased. From
the band alignment by using SE and XPS results, the Fermi level of
Li 3 at.% added ZTO was located at the closest position to the
conduction band minimum. It means that the electron concentration
was increased and it is because of electron generation by lithium
interstitial bonding in ZnO matrix. As the result of PBS Li 3
at.%-ZTO TFT showed improved gate bias stability.
As the result of Li-ZTO TFT characteristic according to the
change of neutron dose, the saturation mobility was increased at 1000
s neutron irradiation time. From the XPS and SE results, chemical
bonding states were not changed, but the Fermi level of 1000 s
irradiated TFT located at the closest position to the conduction band
minimum from the band alignment results. The cause of increasing
saturation mobility is because the electron is easily exited to the
conduction band by increasing D1 state in conduction band edge.