Abstract Details


Hideo Hosono

Professor at Tokyo Instirute

Hideo Hosono

Professor at Tokyo Instirute

Abstract Name:

Finding of donor-donor and donor-acceptor interaction in amorphous IGZO thin films

Symposium:

Symposium A: Materials, Modelling, Simulation & Characterisation

Topic:

A1: Electronic Defects & Transport

Abstract Contributing Authors:

Hideo HOSONO1,2, Hanjun CHO,1 Masatake TSUJI 1 and Junghwan KIM1,3 1 Tokyo Institute of Technology, Yokohama, Japan, 2 National Institute for Materials Science, Tsukuba, Japan, 3 Ulsan National Institute of Science and Technology, Korea

Abstract Body:

Amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) has been widely used in the flat-panel display as the backplane [1]. In recent years, IGZO-TFTs have attracted attention for capacitor-free next-generation memory applications owing to their ultra-low off-current. They require ultra-thin (several nanometers), threshold voltage stability, and strict requirements for precise control of carrier concentration; however, the carrier generation mechanism in AOS remains still elusive. Here, we conducted Hall effects on a-IGZO under various conditions as a function of temperature to elucidate the concentration and energy levels of thermally active shallow donors. In general, the activation energy in n-type semiconductors is negatively correlated with the donor concentration as shown in the following equation  Ea(ND )=Ea(0)-α(ND)(1/3), where Ea(0), α and (ND )(1/3)  indicate activation energy for band conduction at very low doping level, constant for geometrical factors, average distance between ionized donors. Conventional semiconductors and oxide semiconductors have α>0, which indicate increase of activation energy is due to interaction between ionized donors.  However, if there is positive correlation or both of positive and negative correlations occurs for varying film thickness and post-annealing process, it would lead to have novel picture in AOS for TFTs. In this study, we measured temperature dependent Hall effect in various a-IGZO thin films and Hard X-ray Photoelectron Spectroscopy (HAXPES) to observe the electronic states of a-IGZO. Fig. 1 shows the relationship between ND and Ea calculated from the temperature dependence of the Hall effect. When the PO2 during sputtering was reduced to increase the VO, a decrease in Ea was observed with an increase in ND, as shown in the blue plot in Fig. 1. This is the behavior typically seen in common n-type semiconductors. The linear relationship between ND(1/3)  and Ea, indicating that this relationship is due to the interaction between VO’s. By increasing VO by lowering PO2, as shown in Fig. 1(a and b), average separation between donors is getting closer, causing the top of the occupied orbital become shallower due to orbital interaction. This Ea shift continues until the donor levels become shallow near the CBM, eventually reaches degenerate state. However, interestingly, when ultra-thin a-IGZO films, required for next generation memory applications, were fabricated, the Ea showed a positive correlation with defect concentration, as shown in the red plot in Fig 1. Since the relationship between ND and Ea is opposite to donor-donor interactions, it is possible that an unoccupied acceptor level located just below the CBM, interact with a donor as shown in Fig. 1(c and d), results in a deepening of the occupied orbitals. This means the increase in Ea with increasing ND. In the talk, we present these new findings and their responsible model along with influence on TFT performance.

[1]Hosono, H., & Kumomi, H. (Eds.). (2022). Amorphous oxide semiconductors: IGZO and related materials for display and memory. John Wiley & Sons.


Attached Figure:

Fig(ICANS 1 defect).pdf

Submission Type:

Talk

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