Large degree of polarization of photoluminescence caused by anisotropic strain in nonpolar a-plane MgxZn1-xO layers grown by plasma-assisted molecular beam epitaxy

A large degree of polarization (rho) of photoluminescence (PL) approximate to 1 is obtained in each nonpolar a-plane MgxZn1-xO layer grown by plasma-assisted molecular beam epitaxy (MBE) with x = 0.01, 0.03, and 0.10, respectively. Anisotropic in-plane strains are selectively introduced by using foreign substrates and doping with different Mg contents, which strongly modify the valence band structures, leading to anisotropic optical properties. A polarized Raman measurement shows that anisotropic in-plane strains along the y and z axes increase with the increasing Mg contents. Polarized PL spectra show that. gradually increases to 0.97 with decreasing in-plane strains, resulting from an increasing difference in transition energy (Delta E) between E perpendicular to c and E parallel to c caused by a lift of the degeneracy of valence band structures. The obtained highly polarized emission is close to linear polarized light, which is desirable in the backlighting of liquid crystal displays. (C) 2016 Optical Society of America