Characteristics of Rhombohedral (3R) Structure of α-In₂Se₃ Nanosheets by Mechanical Exfoliation

The mechanically exfoliated ultrathin 3R α-In₂Se₃ nanosheets were transferred onto a SiO₂/Si substrate. Using atomic force microscopy, it was confirmed that the transferred α-In₂Se₃ transferred had a thickness of 15–120 nm. The thickness-dependence of Raman peaks of E², A₁¹, E⁴, and A₁² was observed from the Raman spectra. Moreover, the measured photoluminescence peak values in the range of 869–895 nm indicate a blue shift as the thickness decreases. The field-effect transistor based on α-In₂Se₃ exhibited an n-type semiconductor behavior. From the transfer curve at gate voltage of 10 V, the derived values of the mobility and ON/OFF ratio are 24.26 cm² V^{− 1} s^{− 1} and 1.84, respectively. In addition, it was confirmed that the 3R α-In₂Se₃ layers had a high photoresponsivity of up to approximately 34,500 A/W under illumination (λ = 750 nm). Graphical abstract: (Figure presented.)