Interface Engineering to Control Charge Transport in Colloidal Semiconductor Nanowires and Nanocrystals

Colloidal semiconductor nanocrystals (NCs) are a class of materials that has rapidly gained prominence and has shown the potential for large area electronics. These materials can be synthesized cheaply and easily made in high quality, with tunable electronic properties. However, evaluating if colloidal nanostructures can be used as a viable semiconducting material for large area electronics and more complex integrated circuits has been a long standing question in the field. When these materials are integrated into solid-state electronics, multiple interfaces need to be carefully considered to control charge transport, these interfaces are the: metal contact/semiconductor, dielectric/semiconductor and the nanocrystal surface. Here, we use colloidal nanowire (NW) field-effect transistors (FETs) as a model system to understand doping and hysteresis. Through controllable doping, we fabricated PbSe NW inverters that exhibit amplification and demonstrate that these nanostructured materials could be used in more complex integrated circuits. By manipulating the dielectric interface, we are able to reduce the hysteresis and make low-voltage, low-hysteresis PbSe NW FETs on flexible plastic, showing the promise of colloidal nanostructures in large area flexible electronics. In collaboration, we are able to fabricate high-performance CdSe NC FETs through the use of a novel ligand, ammonium thiocyanate to enhance electronic coupling, and extrinsic atom in indium to dope and passivate surface traps, to yield mobilities exceeding 15 cm2V-1s-1. Combining high-mobility CdSe NC FETs with our low-voltage plastic platform, we were able to translate the exceptional devices performances on flexible substrates. This enables us to construct, for the first time, nanocrystal integrated circuits (NCICs) constructed from multiple well-behaved, high-performance NC-FETs. These transistors operate with small variations in device parameters over large area in concert, enabling us to fabricate NCIC inverters, amplifiers and ring oscillators. Device performance is comparable to other emerging solution-processable materials, demonstrating that this class of colloidal NCs as a viable semiconducting material for large area electronic applications.