Enabling and Controlling Negative Photoconductance of FePS₃ Nanosheets by Hot Carrier Trapping

Abstract

to the photon-assisted oxygen desorption from the nanostructure surface, resulting in a decrease of hole concentration. [2] Also, in the case of n-type InAs nanowires, the hot carrier trapping process at the surface gives the reduction of photoexcited charge carriers. [3] Therefore, additional electronic states are always required to compensate photoexcited charge carriers for accessing NPC situation. Nanostructured materials with plenteous surface sites can potentially generate a high density of localized energy states to trap photoexcited charge carriers, which are promising for constructing optoelectronic devices with high-speed frequency response and low power consumption. [3,4] 2D materials have proved to be one of the most promising materials of which the focus has expanded beyond graphene to other layered van der Waals materials with a variety of distinct properties. [5][6][7][8][9][10] A burgeoning research direction goes toward the newly emerged metal phosphorus trichalcogenides (MPTs). [11][12][13][14] MPTs have many fascinating properties as featured in photoelectronic and electronic fields, such as a wide range of indirect bandgap from 1.3 to 3.5 eV, [11] and high carrier mobility. [15] In addition, the introduction of magnetic metal atoms can bring new physical phases, such as antiferromagnetic or ferromagnetic order. [16,17] With these advantages, some works have demon strated that MPTs obtain a remarkable photo response under ultraviolet (UV) illumination 2D materials have aroused tremendous attention in the last decade, and magnetic materials of the 2D scale are rising to prominence in recent years, which may revolutionize current optical and electronic applications. Photoconductivity is a well-known optical and electrical property, which should be positive as the conductivity of material increases typically upon the absorption of electromagnetic radiation. Here, a controllable switch from negative to positive photoconductivity effect of FePS 3 nanosheets is enabled by the modulation of the excitation wavelengths. These effects originate from an ultrafast process of hot carrier trapping, as visualized and investigated by the transient absorption microscopy at a quantitative level. This hot carrier trapping process is about 1.25 ps resulting in a lower diffusion constant state (≈3.5 cm 2 s −1 ), which provides deep insight into the intrinsic properties of 2D FePS 3 for further study. The results demonstrate experimentally the possibility to tune the electronic properties of 2D magnetic materials by an optical way, which not only induces the change in the magnitude but also in the sign, leading to more understandings and possibilities in 2D optoelectronic devices with many unexpected and multifunctional properties.

Spectroscopy and Structural Investigation of Iron Phosphorus Trisulfide—FePS3

“…[ 27 ] Monotonic and predictable absorption edge shift within the temperature range covered by present state‐of‐the‐art thermoelectric cells (200–250 K) [ 46 ] is relevant for extending the usefulness of FePS 3 as the active material for low‐noise cooled photodetectors covering a broad spectral range from near‐infrared up to ultraviolet. [ 27–29 ] The characteristic region of anomalous temperature dependence coincides with a transition from the paramagnetic (PM) to the antiferromagnetic (AFM) phase of FePS 3 (Néel temperature). [ 47–50 ] The same behavior has been observed on a few samples of the synthesized material and during multiple heating/cooling cycles on the same sample, proving good reversibility of the phase transition.…”

“…Iron phosphorus trisulfide, FePS 3 , attracts a lot of attention in that term. It has been shown to exhibit extraordinary photoconductive performance [27][28][29] arising from high carrier mobility and broadband optical absorption above the bandgap (1.2-1.5 eV depending on the experimental technique [23,24,29] ) close to the optimal for solar cells as determined by the Shockley-Queisser limit. Negative photoconductivity [28] has also been observed in thin layers of FePS 3 for illumination with photons of energy around trap states within the conduction band, switchable in sign and magnitude by applying a gate voltage, [27] giving another parameter to control the device performance.…”

“…It has been shown to exhibit extraordinary photoconductive performance [27][28][29] arising from high carrier mobility and broadband optical absorption above the bandgap (1.2-1.5 eV depending on the experimental technique [23,24,29] ) close to the optimal for solar cells as determined by the Shockley-Queisser limit. Negative photoconductivity [28] has also been observed in thin layers of FePS 3 for illumination with photons of energy around trap states within the conduction band, switchable in sign and magnitude by applying a gate voltage, [27] giving another parameter to control the device performance. Despite that, reports on optical properties of FePS 3 at low temperatures, providing details on the typical temperature range of artificially (cryogenics, thermoelectrics) or naturally (space environment [30] ) cooled photodetectors, are lacking.…”

Low‐Frequency Electronic Noise in Quasi‐2D van der Waals Antiferromagnetic Semiconductor FePS3—Signatures of Phase Transitions

“…[25][26][27]58,59] The study, which reported linear I-Vs for FePS 3 devices, was limited to the lower voltage regimes. [60] The exact nature of the non-linearity at high bias voltage is still an open question. While some studies attributed it to the formation of the Schottky barriers at the junction between the channel and the metal contacts, [25][26][27]58] the I-V characteristics of our devices plotted in semi-logarithmic scale (se(c)) suggest deviation from the conventional Schottky barrier thermionic model.…”

Fully Light‐Controlled Memory and Neuromorphic Computation in Layered Black Phosphorus

“…To further understand this unique photoresponse, we propose a comprehensive analytical model which, unlike any previously reported models, [ 25,26,64 ] accounts for both positive and negative photoresponse. For a nonequilibrium system, we summarize a set of equations and consider the frequency‐dependent rate equations governing the densities of photogenerated hot electrons and holes ( n hot and p hot ), trapped holes ( p trp ), and relaxed electrons and holes at conduction and valence band edges (Δ n and Δ p ) in this model.…”