Polarization properties of nonpolar GaN films and (In,Ga)N/GaN multiple quantum wells

Abstract

We have grown GaN films and (In,Ga)N/GaN multiple quantum wells (MQWs) by plasma-assisted molecular-beam epitaxy on γ-LiAlO2(100) substrates. Due to the crystal symmetry of γ-LiAlO2(100), GaN films and (In,Ga)N/GaN MQWs can be realized in a nonpolar (M-plane) configuration, i.e., the c axis of the wurtzite unit cell lies in the growth plane. For compressively, anisotropically strained M-plane GaN films, the band structure of the valence band changes in such a way that the optical transmittance becomes 100% linearly polarized for two orthogonal in-plane directions, where one of these directions is parallel to the c axis of the GaN film. The photoluminescence properties of M-plane In0.1Ga0.9N/GaN MQWs exhibit a strong in-plane optical anisotropy for linear polarization with an energy-dependent polarization degree of up to 96%, which is presumably also due to a large valence-band splitting induced by the large compressive strain in the QWs.