Multifunctional indium selenide devices based on van der Waals contacts: High-quality Schottky diodes and optoelectronic memories

Van der Waals semiconductors, with ultrathin body thickness and dangling-bond-free surfaces, have been employed to fabricate a vast range of electronic and optoelectronic devices such as transistors, photodiodes and memories. The integration of these different functional elements into one single device, usually referred to as multifunctional device, has received great research attention in the recent years. In this work, we realized a multifunctional device, based on the van der Waals semiconductor Indium Selenide (InSe), which can work both as a high-quality Schottky diode with current rectification and photovoltaic characteristics and as a memory. By exploiting the all-dry deterministic transfer fabrication method, we deposited the 2D InSe channel onto pre-deposited graphite and platinum electrodes, whose theoretical work functions differ of similar to 1.0-1.4 eV. Thanks to a controllable InSe air passivation treatment, these devices, which start in a non-rectifying state with negligible electrodes-InSe barriers, gradually evolve into Schottky diodes, presenting a final sizeable Schottky barrier height of 556 +/- 50 meV at the Pt-InSe interface, thus resulting in a gradual tuning of the device photo-responsivity and photovoltaic parameters (such as the open circuit voltage V-oc). The multifunctional capabilities of these devices were demonstrated by using them as optoelectronic memories, which can achieve on-off ratios between the logical '1' and '0' up to 100 and retention times of thousands of seconds. This multifunctional behavior can be ascribed to the traps present in the system, which on one side influences the metal-semiconductor barriers and on the other introduces charge storage capabilities at the base of the memory operation. Our results demonstrate that trap state modulation can be an important tuning knob for thin InSe in the field of electronics and optoelectronics.