An Ultrafast WSe₂ Photodiode Based on a Lateral p-i-n Homojunction

Abstract

High-quality homogeneous junctions are of great significance for developing transition metal dichalcogenides (TMDs) based electronic and optoelectronic devices. Here, we demonstrate a lateral p-type/intrinsic/n-type (p-i-n) homojunction based multilayer WSe2 diode. The photodiode is formed through selective doping, more specifically by utilizing self-aligning surface plasma treatment at the contact regions, while keeping the WSe2 channel intrinsic. Electrical measurements of such a diode reveal an ideal rectifying behavior with a current on/off ratio as high as 1.2 × 106 and an ideality factor of 1.14. While operating in the photovoltaic mode, the diode presents an excellent photodetecting performance under 450 nm light illumination, including an open-circuit voltage of 340 mV, a responsivity of 0.1 A W–1, and a specific detectivity of 2.2 × 1013 Jones. Furthermore, benefiting from the lateral p-i-n configuration, the slow photoresponse dynamics including the photocarrier diffusion in undepleted regions and photocarrier trapping/detrapping due to dopants or doping process induced defect states are significantly suppressed. Consequently, a record-breaking response time of 264 ns and a 3 dB bandwidth of 1.9 MHz are realized, compared with the previously reported TMDs based photodetectors. The above-mentioned desirable properties, together with CMOS compatible processes, make this WSe2 p-i-n junction diode promising for future applications in self-powered high-frequency weak signal photodetection.

p-/n-Type modulation of 2D transition metal dichalcogenides for electronic and optoelectronic devices

“…The high Se/Pt ratio was realized by a slow cool down process with a continuous supply of Se precursor, while the low Se/Pt ratio was achieved by a rapid cool down process followed by Se precursor removal. Besides the in-situ growth presented above, the defects could be also created by post-growth approaches, that all have the advantage of patterned doping capability, for instance, chemical treatment [66], plasma or electron beam etching [68,70,71], and light illumination [72]. A great example of chemical treatment for the intrinsic defect tailoring of MoS2 is presented in Fig.…”

“…metal oxides [70,121,[139][140][141], metal halide [125][126][127][128][129][130], organic molecules [125, 134-136, 146, 149, 150, 152], etc. Surface deposition/coating has the advantages of patterned doping capability, relative low doping temperature, and little crystal damage [129,133,134,153].…”

“…However, some metals are unstable since they are highly active and easy to be oxidized in the air, which requires extra protection through layer passivation. Different from the instable metals, a series of stable metal oxides and carbonates are chosen as dopants for TMDCs doping, for instance, p-type dopants of Mo and W oxides [70,[120][121][122], as well as n-type dopants of Cs2CO3 and Al2O3 [96,[139][140][141]. For Al2O3 doped TMDCs, the n-type doping induced by Al2O3 deposition results from the O vacancies existing at the interface and the methyl group dissociated from the depositing precursor, which created donor states near the conduction band edge of MoTe2 (Fig.…”

“…6(d)). It should be mentioned that using O2 plasma or laser illumination would lead to the surface self-oxidization of TMDCs, which presents equivalent effects to the surface charge transfer doping of metal oxides deposition [70,121,122].…”

Manipulating the Light‐Matter Interaction of PtS/MoS2 p–n Junctions for High Performance Broadband Photodetection

“…It has been demonstrated that through contact engineering by tuning the work function of electrode contact layer, it is able to construct the p‐type contact and result in the fabrication of p‐type transistor. [ 13–15 ] Molecular doping, such as fluoro‐based polymer, could also realize the formation of p‐type electrical property. [ 16–19 ] However, the stability of the adsorbed molecular is still a challenge.…”