Colloidal Monolayer β-In₂Se₃ Nanosheets with High Photoresponsivity

Abstract

We report a low-temperature colloidal synthesis of single-layer, five-atom-thick, β-In2Se3 nanosheets with lateral sizes tunable from ∼300 to ∼900 nm, using short aminonitriles (dicyandiamide or cyanamide) as shape controlling agents. The phase and the monolayer nature of the nanosheets were ascertained by analyzing the intensity ratio between two diffraction peaks from two-dimensional slabs of the various phases, determined by diffraction simulations. These findings were further backed-up by comparing and fitting the experimental X-ray diffraction pattern with Debye formula simulated patterns and with side-view high-resolution transmission electron microscopy imaging and simulation. The β-In2Se3 nanosheets were found to be indirect band gap semiconductors (Eg = 1.55 eV), and single nanosheet photodetectors demonstrated high photoresponsivity and fast response times.

Recent Progress in 2D Layered III–VI Semiconductors and their Heterostructures for Optoelectronic Device Applications

“…Figure e demonstrates that the dominating mechanism of photocurrent generation changes from fast photoconduction at back gate bias of −40 V (OFF state) to high‐gain photogating across the ON state. In the ON state, the photogain is strongly dependent on the gate voltage, showing an ultrahigh photoresponsivity up to around 1 × 10 5 A W −1 at back gate bias of 30 V under illumination of 640 nm laser, which is even superior to that of previously introduced β‐In 2 Se 3 photodetectors . The enhancement of the photoresponse could be attributed to the oxide layer at surface and photogenerated holes trapped in long‐lived states.…”

“…Apart from α‐In 2 Se 3 , the layered β‐In 2 Se 3 has also been developed into photodetectors, exhibiting high photoresponsivity and fast response times as well . Here, monolayer β‐In 2 Se 3 nanosheets have been prepared by a colloidal synthesis technique, resulting in the samples with lateral scale ranged from ≈300 to ≈900 nm.…”

“…The processing temperature (≈200 °C) is much lower than those of techniques for growing 2D In 2 Se 3 , such as PLD, vdWs epitaxy and physical vapor transport . Previous studies indicate that bulk β‐In 2 Se 3 possesses a direct optical bandgap of 1.3 eV, but undergoing a transition to indirect bandgap of around 1.55 eV when the thickness decreasing to monolayer . The photodetector was constructed by dispersing the β‐In 2 Se 3 solution on SiO 2 /Si substrate (Figure c).…”

Versatile Crystal Structures and (Opto)electronic Applications of the 2D Metal Mono‐, Di‐, and Tri‐Chalcogenide Nanosheets

“…M 2 X 3 possesses various crystal structures with different arrangements of atoms in a layer and stacking configurations. In 2 Se 3 has been demonstrated to have five types of crystal phases . The α‐phase and β‐phase are stable in ambient conditions.…”

“…Other phases can be obtained under certain conditions. α‐In 2 Se 3 and β‐In 2 Se 3 are semiconductors possessing the bandgaps of 1.35 and 1.45 eV, respectively, and α‐In 2 Se 3 exhibits better conductivity than β‐In 2 Se 3 . Moreover, Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 are topological insulators.…”