Deep impurity levels in semiconductor superlattices

Abstract
A theory of sp3-bonded substitutional deep impurity levels in periodic N1×N2 GaAs/Alx Ga1xAs superlattices predicts that as the thickness t(GaAs) of each GaAs layer is reduced below a critical value (≲17 Å or N1≲6 for x=0.7) common shallow donor impurities such as Si cease donating electrons to the conduction band and instead become deep traps.