CPM Seminar

Relative size matters: Isoelectronic impurities and alloys

Sébastien Francoeur

École Polytechnique Montréal

Isovalent doping gives direct control over the electronic properties of semiconductors and provides an amazingly flexible way to study and to take advantage of confinement effects. Whereas an isovalent impurity always creates a perturbation to the host band structure, this perturbation is usually small and hybridizes with the host states to remain largely unnoticeable. In this talk, I will discuss the properties of a particular class of isovalent impurities creating a strong perturbation through their markedly different ~Ssize~T and electronic core structure.

An isoelectronic impurity disrupts the local electronic charge distribution and induces a strongly localized potential that, under certain conditions, can capture and retain a charge carrier. I will present our results on nitrogen isoelectronic impurities in GaAs, which create a large number of excitonic bound states. Optically resolving individual impurity centers lifts the orientational degeneracy, reveals critical information on their symmetry and configuration, and exposes their distinctive signatures. These findings allow reconsidering the traditional role given to impurities and open up an interesting approach for the development of an atomic scale electronic. At a higher doping regime, alloys made of isoelectronic impurities have been severely challenging our understanding of semiconductor alloys. Although always present, effects related to atomic scale perturbations reach an unprecedented level in these alloys and result in a radically different behavior. I will present some characteristics of GaAsN and discuss the origin of its non-monotonic band gap dependence and the normally forbidden optical transition. Isoelectronic alloys have opened a new chapter in the physics of semiconductors and motivate us to fully consider the role of disorder on their electronic properties.