WSe₂ Homojunction p–n Diode Formed by Photoinduced Activation of Mid-Gap Defect States in Boron Nitride

A single nanoflake lateral p–n diode (in-plane) based on a two-dimensional material can facilitate electronic architecture miniaturization. Here, a novel lateral homojunction p–n diode of a single WSe2 nanoflake is fabricated by photoinduced doping via optical excitation of defect states in an h-BN nanoflake upon illumination. This lateral diode is fabricated using a mechanical exfoliation technique by stacking the WSe2 nanoflake partially on the h-BN and Si substrates. The carrier type in the part of the WSe2 film on the h-BN substrate is inverted and a built-in potential difference is formed, ranging from 5.0 to 4.50 eV, which is measured by Kelvin probe force microscopy. The contact potential difference across the junction of p-WSe2 and n-WSe2 is found to be ∼492 mV. The lateral diode shows an excellent rectification ratio, up to ∼3.9 × 104, with an ideality factor of ∼1.1. A typical self-biased photovoltaic behavior is observed at the p–n junction upon the illumination of incident light, that is, a positive open-circuit voltage (Voc) is generated, that is, voltage obtained (at Ids = 0 V), and also a negative short-circuit current (Isc) is generated, that is, current obtained (at Vds = 0 V). The presence of built-in potential in the proposed homojunction diode establishes Isc and Voc upon illumination, which can be implemented for a self-powered photovoltaic system in future electronics. The proposed doping technique can be effectively applied to form planar homojunction devices without a photoresist for future electronic and optoelectronic applications.