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 capabl e of simulating potential variations both along the growth direction a nd in the lateral directions. We find that an isolated attractive impu rity in a single barrier can produce a transmission resonance whose po sition and strength are sensitive to the location of the impurity with in the barrier. We also study transmission in the presence of two clos ely spaced impurities as a function of their separation and orientatio n relative to the incident plane wave. Multiple impurities can lead to a complex resonance structure that fluctuates widely with impurity co nfiguration. In addition, impurity resonances can give rise to negativ e differential resistance.