Zhaofu Zhang

Oxide Materials and Devices

The Institute of Technological Sciences, Wuhan University, Wuhan 430072, Chin  a 

Email: zz389@cam.ac.uk

Biography

Dr Zhaofu Zhang received the B.S. degree from Nankai University in 2014, and the Ph.D degree from The Hong Kong University of Science and Technology in 2018. He worked as the postdoctoral research associate in Department of Engineering, Cambridge University. He joined Wuhan University as the tenure-track Professor in May 2022. He has published more than 90 peer-reviewed journal papers. His research interests include the interface and defect engineering in both traditional and novel semiconductors, the rational design of semiconductor devices, as well as the power device fabrication and characteristics.

Abstract for Presentation

P-type oxides in Back-end-of-line Semiconductor Devices

Semiconducting oxides are valuable as thin film displays or solar cell electrodes and are recently of interest as back-end-of-line bipolar devices[1,2]. There are numerous high mobility n-type semiconducting oxides[3,4], but there is a lack of p-type oxides with similar mobility[5]. This led to a search for additional p-type oxides using high-throughput calculations[6-8]. The calculations found a new oxide class like SnTaO6 with low effective hole mass mh*. We find that many of these proposed oxides possess cation s-like lone-pair states. It should be noted that, the proper p-type oxides do not just focus on the low mh*, but look at the compensation by native defects. The low mh* actually occurs as side product of the cation s lone pair hybridizing with O 2p states. The defect energies of some of these oxides are calculated here in detail. SnTa2O6 is found in our work to be promising p-type oxide based on its low effective hole mass owing to its cation lone-pair character, wide stability range, and more importantly, the absence of compensating native defects under O-rich limit(Fig. 1b). The lack of compensation native defects are the key requirements. However, recently Schlom et al. [9] synthesized this material epitaxially and found the films were insulating not p-type under their MBE growth conditions, where O-poor limit was used thus causing the negative formation energy of oxygen vacancies as the compensation centers. The SnTa2O6 and its amorphous phase oxides can still be promising for the back-end-of-line bipolar device applications with
further studies with different synthesis techniques, where the growth conditions should be carefully controlled.

References 
1. S. Salahuddin, et al, Nature Elec. 1 (2018) 442
2. M. Si, P. Ye, et al, Nano Lett. 21 (2021) 500.
3. H. Kawazoe, et al, Nature 389 (1997) 939.
4. Y. Ogo, H. Hosono, APL 93 (2008)032113.
5. J. B. Varley, C. van de Walle, APL 108 (2013)082118.

6. G. Hautier, et al, Nat. Comm. 4 (2013) 2292.
7. R. Woods-Robinson et al, Chem. Mater. 30 8375 (2018).
8. Y. Hu, KJ Cho, et al, Chem. Mater. 33 (2021) 212.
9. M. Barone, D. Schlom et al, JPCC, 126 (2022) 3764.