Structural and optoelectronic properties of cubic Zn1-x-yBexMgySe quaternary alloys nearly lattice matched to GaAs substrate: A density functional investigation

Abstract

Density functional calculations of structural and optoelectronic properties of cubic Zn1-x-yBexMgySe quaternary alloys are carried out considering their nearly lattice matching to GaAs substrate. Calculations ensure that each quaternary alloy is a direct band gap (Γ−Γ) semiconductor. The mBJ-GGA based computed minimum band gap of each alloy is larger that with EV-GGA scheme. Enhancement in beryllium or magnesium composition nonlinearly reduces the lattice constant, but enhances the bulk modulus and minimum band gap of quaternary alloys. Lower effective mass of electrons compared to holes confirms dominant role of electrons in carrier transportation in each specimen. Electronic transitions from occupied Se-4p state of valence band to unoccupied Zn-5s, Mg-3p, Mg-4s, Be-2p and Be-3s states of conduction band collectively contribute intense peaks in ε2(ω) spectra of each quaternary alloy. Quaternary semiconductor with higher band gap possesses lower value of zero-frequency limits in ε1(ω), n(ω) and R(ω) spectra, but requires higher critical point energies in ε2(ω), k(ω), σ(ω) and α(ω) spectra and vice versa. Computed oscillator strength of each quaternary alloy confirms the presence of sufficient number (>200) of electrons in the unoccupied states of conduction band above 27.0 eV of incident photon energy during any optical excitation.