Non-covalent Functionalized Schottky Interface at Ti3C2Tx/n-Si Van der Waals Heterojunction

Low dimensional 2D materials such as graphene and carbon nano tubes have attracted significant attention from the solid-state device community and are considered as a potential candidate electrode to make functional contact with the Silicon (Si) and other industry compatible semiconductors. In this work we envisioned to utilize one such interesting 2D material Ti3C2Tx belonging to a rapidly emerging family of transition metal carbides/nitrides also known as MXene´s to fabricate the classical yet interesting Schottky junctions by simple drop casting of aqueous conducting colloidal solution of Ti3C2Tx on c-Si. Precisely, we anticipate to tune the work function of the Ti3C2Tx as well as the built-in potential of these Ti3C2Tx/c-Si Van der Waals heterojunction through inserting ultrathin interlayer of cationic polyelectrolytes/organic dipoles with a defined dipole moment value. In order to accomplish the interface engineering inclusion poly(ethylene)amine (PEI 0.1%), third generation poly(amido-)amine (PAMAM G3)), were tested between the Ti3C2TX and c-Si substrates. Charge transport properties of the fabricated Schottky devices with the structure of Ti3C2TX/organic dipole (O.D.) /c-Si were evaluated through systematic analysis of the current-voltage (I-V) and capacitance-voltage (C-V) results. I-V measurements under dark conditions revealed that Schottky diodes fabricated with the (PEI 0.1%) and PAMAM G3 interlayers exhibited lowest reverse saturation current density (J0) value and improved built in potential (Vbi) value as compared to the devices with only 2D-Ti3C2Tx as contact. We report reduction in the work function value of Ti3C2Tx from 5.8 eV to 4.2 eV for Ti3C2Tx/PEI (0.1%) and 3.3 eV for Ti3C2Tx/PAMAM G3 heterostructures. On the basis of the inferences drawn from the surface analysis we ascribe this reduction in work function value to the formation of interfacial dipoles at the Ti3C2Tx/O.D. interface. Importantly this study highlights an innovative method to tune the work function of the Ti3C2Tx MXene inclusion of organic dipoles as interlayers.