Semimetal to semiconductor transition in ErP islands grown on InP(001) due to quantum-size effects

Thickness-dependent changes in the electronic states of semimetal ErP islands grown on the InP(001) surface by organometallic vapor-phase epitaxy have been investigated by means of scanning tunneling microscopy/spectroscopy. The normalized differential conductance spectra show a semimetal behavior for the ErP islands (20–50 nm in size) with thickness larger than 3.4 nm, while the spectra taken for the islands thinner than 3.4 nm reveal a semiconducting gap varying to ∼1 eV. The thickness dependence of the observed gap is explained by the energy gap between the electron sublevel and the hole sublevel calculated using a one-dimensional square-well potential model with infinite barriers. The results demonstrate a semimetal to semiconductor transition due to the quantum size effect on the semimetal ErP band structure with a band overlap of -0.3 eV.