Optical evidence for lack of polarization in (1120) oriented GaN/(AlGa)N quantum structures

We apply continuous and time resolved photoluminescence spectroscopy for studying GaN/AlGaN multiquantum wells structures grown on nonpolar a-plane GaN templates. We found that (a) the energy of the emission from the nonpolar samples decreases slightly with the quantum well width, in a manner explained by the quantum size effect only; (b) the energy differences between the absorption and the emission peaks are independent of the well width; and (c) the decay time of the photoluminescence is only slightly dependent on the quantum well width and is quite similar to that of bulk GaN. These observations are markedly different from measurements obtained from conventional polar [0001] oriented quantum well samples. They clearly demonstrate the absence of an electric field in the nonpolar samples. Our observations are favorably compared with an eight bands k center dot P model calculations. (c) 2005 American Institute of Physics.