Self-Forming p–n Junction Diode Realized with WSe₂ Surface and Edge Dual Contacts

Owing to their practical applications, two-dimensional semiconductor p–n diodes have attracted enormous attention. Over the past decade, various methods, such as chemical doping, heterojunction structures, and metallization using metals with different work functions, have been reported for fabrication of such devices. In this study, a lateral p–n junction diode is formed in tungsten diselenide (WSe₂) using a combination of edge and surface contacts. The appearance of amorphous tungsten oxide at etched WSe₂, and the formation of a junction near the edge contact, are verified by high-resolution transmission electron microscopy. The device demonstrates high on/off ratio for both the edge and surface contacts, with respective values of 10⁷ and 10⁸. The diode can achieve extremely high mobility of up to 168 cm² V⁻¹ s⁻¹ and a rectification ratio of 10³. The ideality factor is 1.11 at a back gate voltage V_G = 60 V at 300 K. The devices with encapsulation of hexagonal boron nitride exhibit good stability to atmospheric exposure, over a measured period of 2 months. In addition, the architecture of the contacts, which is based on a single-channel device, should be advantageous for the implementation of more complicated applications such as inverters, photodetectors, and light-emitting diodes.