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

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.