Determination of AlP/GaP band offset considering conduction-band non-parabolicity of GaP and change in exciton-binding energies

Abstract

The well-width (Lz) dependence of photoluminescence (PL) from staggered type-II aluminum phosphide/gallium phosphide (AlP/GaP) indirect-gap quantum wells (QWs) was investigated for determining the AlP/GaP conduction band offset (ΔEc). The PL spectra at 6 K from a series of type-II QWs with various Lz, 0.06–3.8 nm, grown on GaP(001) substrates showed quantum confinement shifts up to 0.324 eV. The strong conduction-band non-parabolicity reported in GaP was taken into account, and we allowed for a wide range of electron longitudinal effective mass me∥*(GaP) from 0.6 to 4.8 m0 as a fitting parameter. The exciton-binding energies (EB) in these QWs were calculated using Leavitte and Little's method [Phys. Rev. B 42, 11774 (1990)] extended for multiple sub-band mixing, considering the range of the me∥*(GaP). With increasing Lz, the calculated EB were found to be reduced, and the symmetry of the exciton hole-envelope functions was found to change. The PL peak energies of the wider QWs (Lz> 1 nm) agreed with the calculation using me∥*(GaP) = 0.6–1.25 m0 but did not agree with the calculation using me∥*(GaP) = 4.8 m0 without considering the non-prabolicity. Correcting the PL peak energies with the calculated EB, we carefully determined ΔEc to be 0.374 ± 0.01 eV.