2D materials have attracted wide interest because of their potential performance and diversity of function as electronic and optoelectronic materials. Growth of transition metal dichalcogenides (TMDs) such as MoS2 and WSe2 typically requires high temperatures (>700 oC) for large domain size and epitaxy. This restricts the applications of these materials, especially considering the growing interest in 2D materials integration with silicon in back-end-of-line (BEOL) applications that require processing temperature < 450 oC. In contrast, group III metal chalcogenides (indium selenide and gallium selenide) possess lower melting temperatures than TMDs and thus high crystal quality films are anticipated at lower growth temperature. In addition, depending on their stoichiometry and phase, they also have a layered structure that offers interesting physical, electronic, and piezoelectric properties down to the monolayer limit. In the case of indium selenide, there is interest in γ-InSe due to its high carrier mobility (>1000 cm2/Vs) and β-In2Se3 and a-In2Se3 which are ferroelectric phases. Despite the intriguing properties, there have been few studies thus far aimed at investigating the epitaxial growth and properties of indium selenide films.
In this study, we demonstrate the growth of β-In2Se3 thin films on various substrates in a vertical cold-wall metalorganic chemical vapor deposition (MOCVD) system at 400 oC using trimethylindium (TMIn) and hydrogen selenide (H2Se) in a H2 carrier gas. The In2Se3 films were grown epitaxially on c-plane sapphire and Si (111) surfaces. The films were identified as β-In2Se3 by both Raman and XRD. A low reactor pressure (100 Torr) and high total gas flow rate were required to suppress gas-phase reactions between TMIn and H2Se based on their Lewis acid and base properties. β-In2Se3 films were formed on both c-plane sapphire and Si (111) surfaces in this work, however, γ-In2Se3 films were synthesized on amorphous SiO2/Si substrates indicating the importance of substrate type determining the crystal structure of the films. Top-gated thin film transistors (TFTs) fabricated on β-In2Se3 thin films reasonable mobility and on/off ratio and therefore offer potential applications in electronic devices.