Chen Shanshan's team has made new progress in the controllable preparation of wide-bandgap ultra-thin two-dimensional gallium nitride

Compared with bulk GaN, 2D GaN has a band gap in the deep ultraviolet region, excellent mechanical strain capacity and unique electron transport properties due to its two-word confinement effect, and has broad application prospects in the field of deep ultraviolet optoelectronic devices and flexible devices. However, due to the bulk structure of wurtzite, 2D GaN is difficult to obtain directly by mechanical exfoliation. At present, it is still a big challenge to prepare large-area 2D GaN with ultra-wide band gap.

Recently, Professor Chen Shanshan's team from the Department of Physics at Renmin University of China used a plasma enhanced chemical vapor deposition system (PECVD) to synthesize large-area ultra-thin, wide-bandgap two-dimensional gallium nitride. Compared with the traditional ammonia, this work uses environmentally friendly nitrogen as a nitrogen source to nitride the gallium oxide template pre-deposited on the silicon wafer (Figure 1). By balancing the nitridation and etching of the nitrogen plasma that occurs simultaneously, the controllable preparation of double-layer gallium nitride is achieved. The experiment found that the gallium oxide template deposited on the bottom layer of the silicon wafer has a strong ability to resist plasma etching due to the strong interaction with the silicon wafer (oxygen plasma pretreatment), and then nitrided to form ultra-thin gallium nitride. Due to the etching effect of nitrogen plasma, the thickness of the ultra-thin gallium nitride obtained by this method is stable and is not affected by the thickness of the initial gallium oxide template. The measurement of the ultraviolet-visible absorption spectrum found that the prepared two-dimensional gallium nitride has an ultra-wide bandgap of 4.9 eV (Figure 3), which is consistent with the theoretical prediction. This experimental work has achieved the controllable synthesis of large-area, wide-bandgap, ultra-thin two-dimensional gallium nitride, which is expected to be further applied in the field of deep ultraviolet optoelectronics. It also provides new ideas and new approaches for the preparation of two-dimensional group III nitrides, and is expected to be extended to the template synthesis of other two-dimensional materials.

Figure 1 Schematic diagram of the principle of synthesizing two-dimensional gallium nitride by template method.

Figure 2 UV-visible absorption spectroscopy to measure the band gap of two-dimensional GaN.

The research results were published online on January 18 with the title "Subnanometer-thick 2D GaN film with a large bandgap synthesized by plasma enhanced chemical vapor deposition" in the Journal of Materials Chemistry A (IF=12.732), and were selected as 2022 JMCA HOT Papers. The co-first authors of the paper are Ph.D. student Zhang Gehui and Master student Chen Luchen from the Department of Physics, and the corresponding authors are Professor Chen Shanshan from Renmin University of China and Associate Professor Zhang Xu from Beijing University of Technology. The related work was funded by the National Natural Science Foundation of China, Beijing Natural Science Foundation and Renmin University of China Talent Cultivation Fund.