IP and OOP ferroelectricity in hexagonal γ-In2Se3 nanoflakes grown by chemical vapor deposition

Abstract Indium selenide (In2Se3) has got much recent attraction in a variety of research areas mainly due to its multiphase structure. Many existing studies, however, have focused on growth of α and β phase, while chemical vapor deposition (CVD) growth of the γ-phase has only been achieved for micon-thick flakes with the assistance of iodine trichloride (ICl3) catalysts. Here, we present the “catalyst-free” CVD growth of β and γ phase In2Se3 flakes with thicknesses down to only a few nanometers. The structural, optical, and ferroelectric properties of the grown samples were investigated carefully by using various techniques. Optical microscope and Raman spectroscopy studies revealed that triangular and hexagonal shaped β and γ phases were grown at different substrate temperatures, respectively. The second-harmonic generation (SHG) measurement confirmed that β has centrosymmetric structure and γ phase has non-centrosymmetric structure. The ferroelectric properties of the γ-In2Se3 were measured along in-plane (IP) and out-of-plane (OOP) directions, for the first time, by employing piezo-force microscope (PFM). The non-monotonic thickness dependence of the ferroelectricity was found and explained with the combination of Raman and SHG measurements. The catalyst-free growth of γ-In2Se3 and the observation of ferroelectricity in it would be a valuable addition in the field of ferroelectric and piezoelectric switching devices.