Quasi-Van der Waals Epitaxial Growth of γ′-GaSe Nanometer-Thick Films on GaAs(111)B Substrates

• Published in: ACS nano 2024-07, Vol.18 (26), p.17185-17196
• Main Authors: Yu, Mingyu, Iddawela, Sahani Amaya, Wang, Jiayang, Hilse, Maria, Thompson, Jessica L., Reifsnyder Hickey, Danielle, Sinnott, Susan B., Law, Stephanie
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X; 1936-086X
• DOI: 10.1021/acsnano.4c04194

GaSe is an important member of the post-transition-metal chalcogenide family and is an emerging two-dimensional (2D) semiconductor material. Because it is a van der Waals material, it can be fabricated into atomic-scale ultrathin films, making it suitable for the preparation of compact, heterostructure devices. In addition, GaSe possesses unusual optical and electronic properties, such as a shift from an indirect-bandgap single-layer film to a direct-bandgap bulk material, rare intrinsic p-type conduction, and nonlinear optical behaviors. These properties make GaSe an appealing candidate for the fabrication of field-effect transistors, photodetectors, and photovoltaics. However, the wafer-scale production of pure GaSe single-crystal thin films remains challenging. This study develops an approach for the direct growth of nanometer-thick GaSe films on GaAs substrates by using molecular beam epitaxy. It yields smooth thin GaSe films with a rare γ′-polymorph. We analyze the formation mechanism of γ′-GaSe using density-functional theory and speculate that it is stabilized by Ga vacancies since the formation enthalpy of γ′-GaSe tends to become lower than that of other polymorphs when the Ga vacancy concentration increases. Finally, we investigate the growth conditions of GaSe, providing valuable insights for exploring 2D/three-dimensional (3D) quasi-van der Waals epitaxial growth.