We demonstrate extraordinary photoconductive behavior in two-dimensional (2D) crystalline indium selenide (In2Se3) nanosheets. Photocurrent measurements reveal that semiconducting In2Se3 nanosheets have an extremely high response to visible light, exhibiting a photoresponsivity of 3.95 × 102 A·W–1 at 300 nm with an external quantum efficiency greater than 1.63 × 105 % at 5 V bias. The key figures-of-merit exceed that of graphene and other 2D material-based photodetectors reported to date. In addition, the photodetector has a fast response time of 1.8 × 10–2 s and a specific detectivity of 2.26 × 1012 Jones. The photoconductive response of α-In2Se3 nanosheets extends into ultraviolet, visible, and near-infrared spectral regions. The high photocurrent response is attributed to the direct band gap (EG = 1.3 eV) of In2Se3 combined with a large surface-area-to-volume ratio and a self-terminated/native-oxide-free surface, which help to reduce carrier recombination while keeping fast response, allowing for real-...

Extraordinary photoresponse in two-dimensional In(2)Se(3) nanosheets.

Properties of gallium selenide single crystal

The progressive stacking of chalcogenide single layers gives rise to two-dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide (InSe) is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness (as large as 0.2 eV for three single layers). First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.

Electronic structure, optical properties, and lattice dynamics in atomically thin indium selenide flakes

Transport and phototransport properties of crystalline indium monoselenide (InSe) doped with a variety of elements are reported. Measured mobilities, lifetimes, and effective diffusion lengths of photoexcited carriers are used to interpret electrical and photovoltaic properties of several different structures. These include p‐n junctions, bismuth/p‐type InSe, platinum/n‐type InSe, and indium tin oxyde (ITO)/p‐type InSe. External solar efficiencies of the best devices are between 5% and 6%. The influence on the efficiency of the various parameters is evaluated, and ways of improvement are discussed.

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Photoconductivity and photovoltaic effect in indium selenide

The electroreflectance and absorption spectra as well as the hydrostatic pressure dependence of the fundamental absorption edge of GeS, GeSe, SnS, and SnSe crystals are investigated in polarized light. The lowest direct energy gaps are found to be 1V1—1V1 (E | | a) and 1Λ4—1Λ4 (E || b) for Ge and Sn monochalcogenides, respectively. The pressure coefficient of the energy gap 1Λ4—1Λ4 dE/AP = = — (1.3 ± 0.1) × 10−4 eV/MPa of SnSe and SnS is almost twice larger than that of the gap 1V1—1V1 in GeSe, GeS, and SnSe. On the basis of these investigations, different absorption mechanisms responsible for the fundamental absorption edge are discussed.



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Optical spectra and energy band structure of layer-type AIVBVI compounds

Photovoltaic efficiency of InSe solar cells

The transport properties of indium monoselenide have been measured in n- and p-type material. Parameters for photoexcited carriers are given. Fabrication procedures for Schottky and p-n diodes are reported. Photovoltaic spectra are fitted with measured values of transport and optical parameters. InSe is shown to be a new material with attractive characteristics for solar energy conversion. Performance of InSe solar cells is discussed.

https://hal.archives-ouvertes.fr/jpa-00244584/document

Photovoltaic effect in InSe - Application to Solar Energy Conversion

Photovoltaic and photoelectronic properties of GaSe and InSe metal-semiconductor contacts are reported. The shape of the spectra, at room temperature, can be interpreted with reasonable values for diffusion length and junction depth. The variation of the spectra with pressure in GaSe and the shape of the low-energy tail in InSe are in concordance with the indirect nature of the lower energy gaps in both compounds. A comparison of these materials with other semiconductors for photovoltaic conversion purposes is given.

Photovoltaic properties of GaSe and InSe junctions

High-pressure effects on some layered semiconductors are reviewed. Pressure coefficients are compared with band structure calculations. Examples of application of high-pressure data to the investigation of basic parameters in lamellar crystals are given. Vibrational properties under pressure are discussed.

J. M. Besson

Papers

Photoconductivity and photovoltaic effect in indium selenide

Photovoltaic efficiency of InSe solar cells

Photovoltaic effect in InSe - Application to Solar Energy Conversion

Photovoltaic properties of GaSe and InSe junctions

High-pressure effects in layer semiconductors