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2D layered germanium selenide (GeSe) with p-type conductivity is incorporated with asymmetric contact electrode of chromium/Gold (Cr/Au) and Palladium/Gold (Pd/Au) to design a self-biased, high speed and an efficient photodetector. The photoresponse under photovoltaic effect is investigated for the wavelengths of light (i.e. ~220, ~530 and ~850 nm). The device exhibited promising figures of merit required for efficient photodetection, specifically the Schottky barrier diode is highly sensitive to NIR light irradiation at zero voltage with good reproducibility, which is promising for the emergency application of fire detection and night vision. The high responsivity, detectivity, normalized photocurrent to dark current ratio (NPDR), noise equivalent power (NEP) and response time for illumination of light (~850 nm) are calculated to be 280 mA/W, 4.1 × 10 9 Jones, 3 × 10 7 W −1 , 9.1 × 10 −12 WHz −1/2 and 69 ms respectively. The obtained results suggested that p-GeSe is a novel candidate for SBD optoelectronics-based technologies. Two-dimensional (2D) materials have chronically been the most widely studied materials, particularly after the successful scotch tape test to exfoliate graphene by Andre Geim and Kostya Novoselov in 2004 1. 2D materials possess excellent electrical and mechanical properties toward diverse electronic device applications. Graphene, being the prototype of 2D materials 2,3 , has been studied broadly for its exotic electrical, optical, and mechanical properties 3,4. Besides, the group-IV transition metal dichalcogenides (TMDs) having a bandgap of around 1 to 2 eV 5-7 have attracted increasing interest because of their promising electronic and optoelectronic device applications 3,8-21. Graphene possesses extremely high carrier mobility (>10 5 cm 2 V −1 s −1), but the absence of band gap limits its electronic and optoelectronic applications 22. Therefore, TMDs with the properties of graphene-like stature, bandgap tunability, weak van der Waals-like forces and stability have intrigued the interest of the scientific community. TMDs are the family of 2D materials having the chemical composition of MX 2 , where M stands for the transition metal elements (M = Mo, W, Ta, Ge…etc) and X for the chalcogen elements (X = Se, S and Te). Among TMDs, Ge-based materials are preferred for applications due to their abundance on earth and environmentally friendly nature 23. With Se, the p-type Germanium from a narrow bandgap semiconductor material as p-GeSe having exciting application in near-infrared (NIR) photodetectors and electron tunnelling devices. p-GeSe has an indirect bandgap of 1.08 eV in the bulk 24,25 , and a direct bandgap of ~1.7 eV in monolayers 24,26,27. Few layers of p-GeSe can be obtained from bulk by mechanical exfoliation method 28. Among the many applications, p-GeSe shows tremendous capability in the realm of photovoltaics, because of its excellent optical, material and electrical properties. Therefore, it is well known as substitution of phosphorene 29. Moreover, GeSe is considered as an amb...

Two-dimensional (2D) heterostructure with atomically sharp interface holds promise for future electronics and optoelectronics because of their multi-functionalities. Here we demonstrate gate-tunable rectifying behavior and self-powered photovoltaic characteristics of novel p-GeSe/n-MoSe2 van der waal heterojunction (vdW HJ). A substantial increase in rectification behavior was observed when the devices were subjected to gate bias. The highest rectification of ~ 1 × 104 was obtained at Vg = − 40 V. Remarkable rectification behavior of the p-n diode is solely attributed to the sharp interface between metal and GeSe/MoSe2. The device exhibits a high photoresponse towards NIR (850 nm). A high photoresponsivity of 465 mAW−1, an excellent EQE of 670%, a fast rise time of 180 ms, and a decay time of 360 ms were obtained. Furthermore, the diode exhibits detectivity (D) of 7.3 × 109 Jones, the normalized photocurrent to the dark current ratio (NPDR) of 1.9 × 1010 W−1, and the noise equivalent power (NEP) of 1.22 × 10–13 WHz−1/2. The strong light-matter interaction stipulates that the GeSe/MoSe2 diode may open new realms in multi-functional electronics and optoelectronics applications.

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The interface architectures of inorganic–organic halide perovskite‐based devices play key roles in achieving high performances with these devices. Indeed, the perovskite layer is essential for synergistic interactions with the other practical modules of these devices, such as the hole‐/electron‐transfer layers. In this work, a heterostructure geometry comprising transition‐metal dichalcogenides (TMDs) of molybdenum dichalcogenides (MoX2 = MoS2, MoSe2, and MoTe2) and perovskite‐ or hole‐transfer layers is prepared to achieve improved device characteristics of perovskite solar cells (PSCs), X‐ray detectors, and photodetectors. A superior efficiency of 11.36% is realized for the active layer with MoTe2 in the PSC device. Moreover, X‐ray detectors using modulated MoTe2 nanostructures in the active layers achieve 296 nA cm−2, 3.12 mA (Gy cm2)−1 and 3.32 × 10–4 cm2 V−1 s−1 of collected current density, sensitivity, and mobility, respectively. The fabricated photodetector produces a high photoresponsivity of 956 mA W−1 for a visible light source, with an excellent external quantum efficiency of 160% for the perovskite layer containing MoSe2 nanostructures. Density functional theory calculations are made for pure and MoX2 doped perovskites’ geometrical, density of states and optical properties variations evidently. Thus, the present study paves the way for using perovskite‐based devices modified by TMDs to develop highly efficient semiconductor devices.

Based on this, 2D transition metal chalcogenide (TMD) has gained much attention as an excellent alternative to graphene. TMDs have unique properties that are useful for logic devices, such as bandgap tunability (approximately 1.3-1.9 eV) without surface dangling-bond, controllable valley and spin polarization, high I on /I off current ratio up to 10 8 in field-effect transistors (FETs), outstanding carrier transport mobility for both holes and electrons, high stability, and most importantly the exhibition of both unipolar as well as ambipolar behavior. Various 2D materials have been explored over the few past years and among the 2D transition metal chalcogenides (TMDs), WS 2 , WSe 2 , and MoS 2 are suitable for semiconductor devices. [2] Particularly, the semiconducting TMDCs exhibit compelling photovoltaic characteristics because of their tunable bandgap and relatively high mobilities. [3] Until now, the researchers have particularly focused on the electrical and photovoltaic properties of the II-VI compounds because of their excellent quantum-size effects and stable electrical behavior. Conversely, the IV-VI p-type TMDs, particularly GeSe, did not receive much attention despite their potential applications in photovoltaics (PV), transparent thin-film transistors, memristors, and flexible electronics. [4] GeSe is a layered p-type material with a relatively narrow bandgap and is utilized in electron tunneling devices and photo detectors. The direct (monolayer) and indirect (bulk) bandgaps of GeSe are approximately 1.7 and 1.08 eV, respectively. [5] GeSe has unique optical and electronic properties, and its optical properties are dominated by excitonic effects. [6] In 2D materials, the saddle points in electronic structure give rise to the diverging density of states. This leads to some intriguing physical phenomena that help improve optical absorption. GeSe possesses saddle points in both the highest valence band and the lowest conduction band. [7] Moreover, similar to the IV-VI chalcogenides, GeSe has a direct bandgap, and the indirect and direct bandgaps lie close to each other, making it promising for solar photovoltaic applications. [8] Despite some theoretical research on GeSe, not much attention has been paid to the heterojunctions (HJs) of GeSe and 2D n-type

Van der Waals (vdW) heterostructures composed of atomically thin two‐dimensional (2D) materials have more potential than conventional metal‐oxide semiconductors because of their tunable bandgaps, and sensitivities. The remarkable features of these amazing vdW heterostructures are leading to multi‐functional logic devices, atomically thin photodetectors, and negative differential resistance (NDR) Esaki diodes. Here, an atomically thin vdW stacking composed of p‐type black arsenic (b‐As) and n‐type tin disulfide (n‐SnS2) to build a type‐III (broken gap) heterojunction is introduced, leading to a negative differential resistance device. Charge transport through the NDR device is investigated under electrostatic gating to achieve a high peak‐to‐valley current ratio (PVCR), which improved from 2.8 to 4.6 when the temperature is lowered from 300 to 100 K. At various applied‐biasing voltages, all conceivable tunneling mechanisms that regulate charge transport are elucidated. Furthermore, the real‐time response of the NDR device is investigated at various streptavidin concentrations down to 1 pm, operating at a low biasing voltage. Such applications of NDR devices may lead to the development of cutting‐edge electrical devices operating at low power that may be employed as biosensors to detect a variety of target DNA (e.g., ct‐DNA) and protein (e.g., the spike protein associated with COVID‐19).

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