Ultraefficient Ultraviolet and Visible Light Sensing and Ohmic Contacts in High-Mobility InSe Nanoflake Photodetectors Fabricated by the Focused Ion Beam Technique

Abstract

A photodetector using a two-dimensional (2D) low-direct band gap indium selenide (InSe) nanostructure fabricated by the focused ion beam (FIB) technique has been investigated. The FIB-fabricated InSe photodetectors with a low contact resistance exhibit record high responsivity and detectivity to the ultraviolet and visible lights. The optimal responsivity and detectivity up to 1.8 × 10 A W and 1.1 × 10 Jones, respectively, are much higher than those of the other 2D material-based photoconductors and phototransistors. Moreover, the inherent photoconductivity (PC) quantified by the value of normalized gain has also been discussed and compared. By excluding the contribution of artificial parameters, the InSe nanoflakes exhibit an ultrahigh normalized gain of 3.2 cm V, which is several orders of magnitude higher than those of MoS, GaS, and other layer material nanostructures. A high electron mobility at room temperature reaching 450 cm V s has been confirmed to be one of the major causes of the inherent superior PC in the InSe nanoflakes. The oxygen-sensitized PC mechanism that enhances carrier lifetime and carrier collection efficiency has also been proposed. This work demonstrates the devices fabricated by the FIB technique using InSe nanostructures for highly efficient broad-band optical sensing and light harvesting, which is critical for development of the 2D material-based ultrathin flexible optoelectronics.

Ga2Se3 Defect Semiconductors: The Study of Direct Band Edge and Optical Properties

“…When photons with power P are incident on a photoconductor, the photocurrent is defined by i p = ( q / E )· P ·η·Γ, where E is the photon energy (in eV) and η is the quantum efficiency (#electrons/#photons). Because the photoconductive gain Γ is dependent on the bias ( V ) and geometry ( l ) we can further use a normalized gain, which is expressed by the product of lifetime, mobility, and quantum efficiency as 49 where R is the responsivity given by R = i p / P , and q is the charge. The DC responsivity of Ga 2 Se 3 is R = 3.24 A/W.…”

Liquid Phase Exfoliated Indium Selenide Based Highly Sensitive Photodetectors

“…Extrinsic factors due to the photodetector design (e.g., short channel length) may raise the responsivity as well 18,25. Moreover, the presence of photoconductive gain mechanisms in β‐InSe also contributes to the high responsivity, multiplying the number of electrons flowing in the device per absorbed photon 26. In particular, the presence of traps that reduce the mobility of minority carriers (holes) in the material, results in the circulation of photogenerated electrons multiple times through the device before recombination 19.…”

Solution‐Based Processing of Optoelectronically Active Indium Selenide

“…Layered indium selenide (InSe) has emerged as a leading successor to transition metal dichalcogenides (TMDCs) for high‐performance optoelectronics due to its exceptional electronic properties and direct bandgap at all thicknesses in excess of three layers . Bulk InSe crystals possess a 1.3 eV direct bandgap and consist of in‐plane covalently bonded Se–In–In–Se layers that interact via weak out‐of‐plane van der Waals bonding .…”

“…Such postprocessing ultimately compromises material properties (Figure S1, Supporting Information) and leads to aggregation due to slow solvent evaporation, hindering thin‐film assembly and degrading device performance . For example, a photoelectrochemical‐type photodetector of InSe nanosheets dispersed in NMP via LPE has been recently reported with significantly inferior photoresponsivity (≈4.8 µA W −1 ) than micromechanically exfoliated flakes (10 7 A W −1 ) …”