The Study on Low Hole Effective Mass P-Type Metal Oxide Materials and Thin Film Transistor Device Fabrication

Investigation on finding suitable materials for producing ^-type transparent conducting oxides (TCOs) has been heavily focused to realize transparent electronic devices. Tin monoxide (5n0) is one of the promising p-typQ candidates as its valence band edge possesses the more spatially spread Sn Ss2 and O 2p hibridized orbitals that allow a direct overlapping between their neighboringcations leading to a higher dispersion of valence band and low hole effective mass. On the other hand, Sn vacancy (^) is introducing hole by inducinga band deformation close to the top of valence bandforming a shallow acceptor-like band states which can be easily occupied by electrons from valence band maximum (VBM). However, the existences of those conditions are energetically contradictory. The prefers to occur in an O-rich condition whereas the delocalized states desired for holes transport require oxygen vacancy (V0) and tin interstitial ) defectswhich both can strengthen Sn metallic contribution into the VBM (O-poor condition). This situation realizes that a highly accurate control of amount of oxygen incorporated in the fabrication process is crucially requiredtoreach an optimum combinationbetween both native defects, i.e. producing a p-typQ a — SnO phase with slightly embedded p — Sn to enhance the mobility. In view of these issues, we proposed a comparison and systematical study in fabrication of the p-typQ SnO thin films by utilizing several deposition techniques, such as pulsed DC reactive sputtering, atomic layer deposition, e-beam evaporation, and ion-assisted beam deposition, to seek an optimum method and achieve a better quality of /?-type SnO with higher mobility. Considering the thermal sensitivity of SnO which can easily oxidize and transform into n-typQ SnO2 ? we focus on establishing the low temperature deposition processes with additional post-deposition annealing in vacuum"V2 ambient to awake its higher crystallinity. Moreover, we proposed bilayer and multilayer /?-type structures by depositing the other/?-type materials, i.e.Cu20, Li：ZnO or NiO, on the top of SnO films to prevent the ambient oxygen diffusion which significantly degrade^打O conductivity. Afterwards, the comparison between these /?-type bilayers and several non /?-type metal oxides (SW2rSiNrAl203r etc) abilities as the capping layer would be studied. Furthermore, beside of the simple oxide of SnO^ the ternary structure of low hole effective mass candidate materials, such as K2Sn203：) RbSn203 and so on, would be also investigated by using similar methods. Finally, we would demonstratethe fabrication of thin film transistor and its complementary inverter circuit to verify the practical use of our fabricated p-typQ thin films. In this part, we could design the devices by employing the activelayer SnO^ bilayer, multilayer and ternary compound thin films with an additional capping layer on the outer side of the device to promote its durability.

Project ID:PB10312-0102
External Project ID:MOST103-2221-E182-074