Neutral impurities in tunneling structures

We examine transport in single and double barrier tunneling structures with neutral impurities. For this purpose, we have developed a three-dimensional, tight-binding supercell model of quantum transport capable of simulating potential variations both along the growth direction and in the lateral directions. We find that an isolated attractive impurity in a single barrier can produce a transmission resonance whose position and strength are sensitive to the location of the impurity within the barrier. We also study transmission in the presence of two closely spaced impurities as a function of their separation and orientation relative to the incident plane wave. Multiple impurities can lead to a complex resonance structure that fluctuates widely with impurity configuration. In addition, impurity resonances can give rise to negative differential resistance.