Strain effect on direct- and indirect-gap band lineups of GaAs1- x P x /GaP quantum wells

Strain effect on direct- and indirect-gap band lineups of strained GaAs₁- _x P _x /GaP quantum wells with a wide range of x is studied using photoluminescence (PL) and photoreflectance (PR) spectroscopy. By comparing the transition energies obtained by PL and PR measurements with the calculation based on the effective mass approximation, it is found that the band lineups of strained GaAs_{1- x} P _x /GaP QWs on GaP substrates at any x are of type I at the X and Γ point and that the valence band offset of heavy hole is 506(1 - x) meV. As a result, it is deduced that biaxial compressive strain makes the energy gap of GaAs_{1- x} P _x alloys grown on GaP substrates indirect at any x.