In spite of the efforts to investigate the physics of resonance tunneling, it has not been fully understood. One such unexplained problem is whether the experimentally observed negative resistance is due to resonant tunneling or sequential tunneling. As seen, the WKB approach fails to provide any insight into this problem.
The path integral method, developed by Richard Feynman \cite{Das_2006}, is an alternative formulation of quantum mechanics and has the advantage of approaching the problem by considering the electrons as classical particles. Since contributions from various possible paths of the electron through the double barrier can be considered (Figure \ref{fig:paths}), this should give a deeper understanding into the phenomenon of resonant tunneling and negative resistance.