Interface states can occur in semiconductor heterojunctions whenever a significant perturbation is present across the interface, for example, interface defects, lattice mismatch, change of sign in the effective mass, or sharp variations in the potential. We discuss here a different type of natural interface states appearing in perfectly coherent and isovalent III–V heterojunctions even in the absence of such extreme perturbations. Using atomistic empirical pseudopotential calculations we find that this is a general phenomenon occurring whenever the junction is formed by two semiconductors having their respective conduction band minima in two different valleys which: (i) fold into the same $\vec{q}$ point of the two-dimensional Brillouin zone and (ii) are allowed by symmetry to couple at this point $\vec{q}$. In this case, the system manifests two potential wells of opposite attractiveness, such as a well for $\Gamma$ states and a barrier for $X$ states. For InP/GaP this leads to the formation of an interface-localized state already in a single heterojunction, lying energetically between the $\Gamma$ edge of InP and the $X$ edge of GaP. When the InP/GaP quantum well is formed, this single state evolves into a pair of interface-localized states, located deep in the band gap. Because of their mixed $\Gamma -X$ character, these interface-localized states possess a strong optical signature. This new understanding allows us to provide a different interpretation to the previously observed photoemission data for InP/GaP quantum wells and dots. We find analogous states in GaAs/AlAs and GaAs/GaP but now these levels are resonant within the continuum of states of the matrix conduction band and are therefore less pronounced.

• Received 13 April 2011
• Publisher error corrected 22 September 2011

DOI:https://doi.org/10.1103/PhysRevB.84.125315