SPST Research Group Teamwork Leads to Discovery of New Semiconductor

ON2018-10-08TAG: ShanghaiTech UniversityCATEGORY: Published Research

Recently, successful teamwork by several SPST research groups (including those of Professors Chen Yulin, Liu Zhongkai,  Xue Jiaming and Li Gang) and Peking University Professor Peng Hailin’s group has made remarkable progress in the understanding of the electronic structures of a new layered oxide semiconductor Bi2O2Se. Their work was published in the September issue of Science Advances, with the title of “Electronic Structures and Unusually Robust Bandgap in an Ultrahigh Mobility Layered Oxide Semiconductor, Bi2O2Se.”

Semiconductors are essential materials in the modern world affecting our everyday life, and the search for new materials with superior electronic properties is critical to the development and prosperity of the semiconductor industry. In the past decade, 2D materials (e.g. graphene, TMDs, black phosphorus) have grown as promising candidates with great potential for future electronic applications. However, the drawbacks of these new materials (e.g. the zero or very small gap in graphene, the relatively low carrier mobility in TMDs, and the instability of black phosphorus in ambient environments have created a major challenge for the search for semiconductor materials with high carrier mobility, moderate bandgap, and ambient environment stability.

Recently, Bi2O2Se, an air-stable layered oxide, has emerged as a promising new semiconductor with excellent electronic properties. Its layered nature (Figure 1a) makes it ideal for fabricating electronic devices down to few atomic layers (even monolayer) with high carrier mobility (~28900 cm2/Vs at 1.9 K), superior current on/off ratio (>106) and moderate band gap (~0.8 eV). These attractive properties, together with its stability in ambient environment and easy accessibility (bulk crystal, thin film, and nano-structures are all readily accessible), make Bi2O2Se a promising semiconductor candidate for future ultra-small high-performance and low-power electronic devices. Furthermore, the structural compatibility between Bi2O2Se and interesting perovskite oxides (e.g. cuprate high transition temperature superconductors and commonly used substrate material SrTiO3) makes it possible for hetero-structures between Bi2O2Se and these oxides to be platforms for realizing novel physical phenomena.

In their recent work, the teams of SPST combined different experimental techniques, including angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM) to fully visualize the electronic structures of this promising new semiconductor with key parameters crucial for the device applications (Figure 1b); and understand its unusually robust band gap (even with up to 50% of the surface impurities, see Figure 1c) with the help of ab initio calculations (Figure 1d).

The study credited Dr. Chen Cheng and Dr. Wang Meixiao were as co-first authors; Professor Chen Yulin and Professor Liu Zhongkai’s groups carried out the ARPES measurements; Professor Xue Jiaming’s group carried out the STM study; and Professor Li Gang’s group carried out the ab initio calculations. Their teamwork was jointly supported by the national key R&D program of China, National Natural Science Foundation of China and Bureau of Frontier Sciences and Education, Chinese Academy of Sciences.

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Figure 1. a. Layered crystal structure of Bi2O2Se. b. 3D band structures showing the conduction band (CB, valance band) and the band gap. c. Surface topography of Bi2O2Se with atomic resolution and the distribution of Se-defects. d. Comparison of the density of states (DOS) between experiments and calculations.