Hydrogen Incorporation Modulates Subgap Density of States in Amorphous InGaZnO Thin-Film Transistors

Abstract

Incorporation of hydrogen into the channel layer of an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor leads to a negative shift in the transfer curve threshold voltage; the magnitude of the threshold voltage shift increases with increasing hydrogen content. Although several atomic models for hydrogen incorporation into a-IGZO have been proposed, hydrogen-induced changes in the sub-gap density of states have never before been directly measured. By employing ultrabroadband photoconduction (UBPC),1,2 we directly observe a large increase in the near-valence band UBPC response in hydrogen-enriched devices; the increase in UBPC response scales with hydrogen concentration.3 This UBPC trend is consistent with the formation of OH states resulting from the interaction of incorporated hydrogen with oxygen already present in the a-IGZO channel layer and explains the observed negative threshold voltage shift in the device transfer curve. K. T. Vogt, C. Malmberg, J. Buchanan, G. Mattson, M. Brandt, D. Fast, P. H.-Y. Cheong, J. F. Wager, M. W. Graham, (2020) Ultrabroadband Density of States of Amorphous In-Ga-Zn-O, Phys Rev Res, 2, 033358K. T. Vogt, G. W. Mattson, J. F. Wager, M. W. Graham (2020) Ultrabroadband Photoconduction Response of Sub-gap Defects in Amorphous In-Ga-Zn-O Thin Film Transistors, ECS Transactions, 97 (7), 339-357G. W. Mattson, K.T. Vogt, C. Malmberg, P. H.-Y. Cheong, J. F. Wager, M. W. Graham, (2020) Effect of hydrogen incorporation on sub-gap density of states in amorphous InGaZnO thin-film transistors, Proc. SPIE, Oxide-based Materials and Devices XI, 112811G, doi.org/10.1117/12.2545439 Figure 1