Novel Materials for Optoelectronics

Heterovalent semiconductor heterostructures, unlike isovalent semiconductor heterostructures, exhibit electronic properties strongly dependent on the detail of the interface atomic structure. Heterojunction band offsets, and therefore carrier injection and confinement, can in principle be modified by acting on the growth protocol and interface composition profile. The authors discuss examples of III-V/IV/III-V single and multiple quantum well structures (with IV = Si, Ge and III-V = GaAs, AlAs) as well as II-VI/III-V and II-VI/IV/III-V heterostructures grown by molecular beam epitaxy and examined by a variety of in-situ and ex-situ characterization techniques. Large deviations from the commutativity and transitivity rules of heterojunction band offsets in these systems are related to the establishment of inequivalent local interface environments. Such deviations are likely to be exploited first in a variety of optoelectronic devices to tune the band alignment.