Strong Quantum Confinement Effect in the Optical Properties of Ultrathin α‐In₂Se₃

Abstract

This is the post-peer reviewed version of the following article: J. Quereda et al. "Strong quantum confinement effect in the optical properties of ultrathin α-In2Se3".Advanced The isolation of atomically thin semiconductors has attracted the interest of the nanoscientists as these materials can complement graphene in those applications where its lack of an electronic band gap hinders its use. [1][2][3][4][5] In fact, two dimensional semiconductors have been recently employed in the fabrication of field effect transistors, [6,7] photodetectors [8][9][10][11][12][13][14] and solar cells. [15][16][17][18][19] Inherent to their reduced out-of-plane dimension, atomically thin semiconductors present a marked thickness-dependent band structure due to the quantum confinement of the charge carriers. For instance, the band gap in Mo-and W-based transition metal dichalcogenides increases from its bulk value (~1.3 eV, indirect gap) up to 1.9 eV (direct gap) in the single-layer limit. [20,21] More recently, black phosphorus has also shown a pronounced thickness-dependent band gap ranging from ~0.3 eV (direct gap) for bulk to ~1.75 eV (direct gap) for single-layer black phosphorus. [22] This thickness-dependent band gap can be very advantageous for applications as photodetectors as one can select the sensing photon energy window by simply selecting the right material thickness for the photodetector device. Up to now, however, there is a broad spectral window from 2.0 eV to 3.0 eV uncovered by 2D materials that could be very relevant for applications requiring 'solar blind' This is the post-peer reviewed version of the following article: J. Quereda et al. "Strong quantum confinement effect in the optical properties of ultrathin α-In2Se3". In this work we demonstrate a very strong quantum confinement effect in the optical properties of atomically thin α-In 2 Se 3 crystals. We observe a marked thickness-dependent shift in the optical absorption spectra acquired on mechanically exfoliated Figure S1). In order to study the optical absorption of the In 2 Se 3 crystals we used a home-made hyperspectral imaging setup, described in detail elsewhere.[25] The hyperspectral imaging is carried out by sweeping the excitation wavelength in steps and acquiring transmission mode images of the In 2 Se 3 crystals for each wavelength.The collected data is then arranged in a three-dimensional matrix, being the first two matrix According to Tauc et al. [26] , near the absorption edge the absorption coefficient of a direct-gap semiconductors iswhere A is a material-dependent constant and E g opt is the optical energy gap of the material.Equation (2) can be rewritten asThis is the post-peer reviewed version of the following article: J. Quereda et al. "Strong quantum confinement effect in the optical properties of ultrathin α-In2Se3".Advanced The usual method for determining the value of E g opt involves representing (αℏω) 2 versus the photon energy, ℏω, and fitting the absorption band edge to a linear function. According to Equation (3), the int...

High Responsivity and Photovoltaic Effect Based on Vertical Transport in Multilayer α‐In2Se3

“…The Φ b1 and Φ b2 are the barrier heights at Au/α‐In 2 Se 3 and ITO/α‐In 2 Se 3 , respectively. Considering the effective electron mass in α‐In 2 Se 3 as m * = 0.13 m, where mo is the free electron mass, the effective area of the device A = 25 μm 2 , temperature ( T ) = 300 K, and the dark I – V curve is fitted to a nonlinear equation, as shown in Figure a. By fitting the curves, ideality factors of 1.03 and 1.05 are estimated for the Au/α‐In 2 Se 3 and ITO/α‐In 2 Se 3 junctions, respectively.…”

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

“…Apart from indium monochalcogenides, In 2 X 3 (X = S, Se, Te) is another intriguing group of 2D layered III–VI family, which has already found a series of proof‐of‐concept applications, such as photodetectors, solar cell, memory devices, benefiting from their direct bandgap, high efficiency of light absorption, large carrier transport mobility, and ferroelectricity . In this subsection, photoconductors/phototransistors based on In 2 S 3 and In 2 Se 3 are reviewed and discussed.…”

Curvature-dependent flexible light emission from layered gallium selenide crystals

“…So far, many researchers are still keen to explore mechanisms and develop methods for tuning bandgap in semiconductors. The methods include changing ambient temperature, 11 strain engineering, 12 changing thickness of compound semiconductor from bulk crystal to thin layer, 13,14 exerting an external electric eld,…”