The Influence of Anion Composition on Subgap Density of States and Electrical Characteristics in ZnON Thin-Film Transistors

The influence of anion composition on the electrical characteristics of amorphous zinc-oxynitride thin-film transitors (TFTs) is investigated and quantitatively modeled, with emphasis on the subgap density of states (DOS). As the ratio of N to (N + O) increases, the density of valence band tail states increases, followed by narrowing of the bandgap and a decrease in the density of conduction band tail states, which in turn is followed by either a higher field-effect mobility or a better subthreshold swing; each of these effects is explained. Furthermore, the anion composition dependence of the transconductance degradation at a high bias is analyzed on the basis of the proposed model. In addition, the effects of the N/(N + O) ratio on carrier density and field-effect mobility are quantitatively explained by the ionized nitrogen vacancy (V-N(1.3+)) model observed in shallow donor peak in the DOS and by the charge-controlled mobility model, respectively. Finally, the effect of nanocrystalline structure mixed with amorphous on transport properties is discussed.