Theoretical investigation of optical polarization properties in Al-rich AlGaN quantum wells with various substrate orientations

The optical polarization properties of Al-rich AlGaN thin quantum wells on AlN substrates with various substrate orientations are numerically calculated using a 6×6 k⋅p Hamiltonian. The calculation results show that the predominant polarization direction abruptly switches from the in-plane direction to the c-axis direction at an Al composition of ∼0.76 in quantum wells on c-plane substrates. It is also shown that the polarization characteristics drastically change by small inclination of the substrates due to valence band mixing effects. It is found that the use of the vicinal substrates as well as semipolar and nonpolar substrates could be beneficial in improving optical device performance.