Piezotronic graphene barristor: Efficient and interactive modulation of Schottky barrier

The piezopotential generated in non-centrosymmetric crystals under external mechanical stimuli can be exploited to modulate the contact characteristics at the metal-semiconductor interface. The extent of electric modulation by the piezopotential was found to be moderate. This is mainly because the piezopotential was designed to alter the band bend of the semiconductor layer, which changed the injection barrier by 0.1 eV. We propose an efficient method to utilize the piezopotential for modulating Schottky barrier, i.e. piezotronic graphene barristor. This was done by capacitively coupling the piezoelectric material with a Schottky barrier (SB)-tunable graphene electrode, using an ion gel electrolyte. Through capacitive coupling, the piezopotential could modulate the work function of a graphene electrode by 0.89 eV. This was visualized directly using Kelvin probe force microscopy experiments for the first time. A large change in the work function of graphene allowed effective tuning of the height of the SB formed at the graphene/semiconductor junction. Consequently, a piezoelectric nanogenerator (PENG) could change the current density of the semiconductor layer by more than three orders of magnitude with strain, and yield a high current density larger than 10.5 A cm^-2. Multistage modulation of the height of the SB at the junction was also successfully demonstrated by integrating two PENGs with ion gel. This work presents an efficient method for harnessing the piezopotential generated from PENG to actively control the operation of flexible electronics through external mechanical stimuli.