Among common semiconductor devices are the diode, field effect transistor, and bipolar junction transistor (BJT). Thin-film analogues of the first two exist and enable commercial products, such as flexible displays and thin-film solar cells. The thin-film BJT has, however, been elusive. Inorganic semiconductor processing steps for deposition and doping required for BJTs are ill-suited for making thin-film BJTs. On the other hand, the ability to deposit organic semiconductor films at low temperature, control their thickness down to the nm range, engineer interfaces with well-defined energy structures, and chemically dope the films should allow for fabricating and demonstrating a thin-film BJT.
The Seed 2 project aims at investigating the interplay between doped organic molecular films, with the ultimate goal of fabricating and testing p-n type heterojunctions that are central to an organic BJT. Central issues for the realization of molecular BJTs are the controlled n- and p-type doping of the emitter, base and collector sections of the device, and the transport of carriers via diffusion through the base. Carrier transport in molecular films is negatively impacted by disorder-, defect- and impurity-induced electronic traps and tail gap states, which decrease mobility and act as recombination centers. In our project, chemical n- and p-doping not only serves to establish the p-n-p (or n-p-n) structure of a BJT, but is also used to passivate, or de-activate, these traps and gap states, thereby improving transport.
Barry Rand (Electrical Engineering)
Antoine Kahn (Electrical Engineering; Engineering and Applied Science)