Compelling Evidence for the ε‐Phase InSe Crystal by Oblique Incident Second Harmonic Generation. Issue 19 (11th July 2022)

• Record Type: Journal Article
• Authors: Sun, Zeyuan; Zhang, Yu; Qian, Jimin; Qiao, Ruixi; Li, Xian; Wang, Zerui; Zheng, Changlin; Liu, Kaihui; Cao, Ting; Liu, Wei‐Tao; Wu, Shiwei
• Is Part Of: Advanced optical materials. Volume 10:Issue 19(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-07-11
• Subjects: InSe -- polytypes -- second harmonic generation -- stacking order; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202201183
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Indium selenide (InSe), a layered semiconductor with direct band gap and high carrier mobility, holds promising applications in bendable electronics and ultrafast optoelectronics. Yet its crystal structure exhibits polytypism with four different stacking orders (γ‐, ε‐, β‐ and δ‐phases), arising from the weak van der Waals interlayer coupling. These phases are nearly‐degenerate in energy but are predicted to have contrasting electronic structures for versatile applications. It remains highly challenging to distinguish between these polytypes due to the lack of noninvasive tools that are sensitive enough to the interlayer structural variations. Here, the unambiguous discrimination of different InSe polytypes using symmetry‐sensitive oblique incident optical second harmonic generation (SHG) is demonstrated. Surprisingly, the ε‐phase is found to be dominant, although the samples from two popular commercial vendors (2D Semiconductors and Six Carbon Technology) are claimed to be the γ‐phase. These results would help promoting the precise application of InSe crystal for piezoelectric transducer and strain sensing, as well as showing the oblique incident SHG to be a powerful structural analytical tool for van der Waals layered materials. Abstract : The stacking polytype of a layered direct‐gap semiconductor, indium selenide (InSe), is scrutinized by symmetry‐sensitive oblique incident second harmonic generation (SHG). The dominance of ε‐phase in InSe crystals is surprisingly found, which has been mislabeled as the most stable γ‐phase by two popular commercial vendors. The work also demonstrates that oblique incident SHG is a powerful structural analytical tool for van der Waals layered materials.