Cathodoluminescence spectroscopy of epitaxial-lateral-overgrown nonpolar (11-20) and semipolar (11-22) GaN in relation to microstructural characterization

Abstract

Low temperature spatially resolved cathodoluminescence was carried out on GaN films grown by the epitaxial-lateral-overgrowth (ELO) technique with the nonpolar (11-20) and the semipolar (11-22) orientations on R- and M-sapphires, respectively. Defect related optical transitions were identified and their localization was correlated to different regions of ELO. The sample microstructure was further investigated by plan-view and cross-section transmission electron microscopies. It is shown that the defect related emissions are mainly localized in the seed of the samples, but different defects occur as well in the wings, especially in the case of nonpolar GaN. The structural defect densities are lowest in the overgrown wings of semipolar GaN. In particular, the [0001] wing region of semipolar ELO-GaN is almost defect-free with a cathodoluminescence spectrum dominated by the GaN band-edge emission at 3.476eV.

Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy

“…Our top view monochromatic CL map taken for emission at 3.417 eV, shown in Fig. 1͑b͒, confirms that intense emission related to BSFs comes from the −c ELO wings, where it presents a rather spotty distribution and, above all, 13 from the window region, where it has the aspect of dashes oriented along the c-plane.…”

“…In terms of spatial distribution of the BSFs, previous studies by transmission electron microscopy 13 reported that their density is higher by two orders of magnitude in the −c ELO wing and in the window region than in the +c wing. Our top view monochromatic CL map taken for emission at 3.417 eV, shown in Fig.…”

Structural anisotropy of nonpolar and semipolar InN epitaxial layers

“…42 The growth rate of the wurtzite In-polar plane may be expected to be grater than the growth rate of the N-polar counterpart in similarity to GaN. 8,43 This can qualitatively explain the detected higher volume fraction of ͑1011͒A domain compared to ͑1011͒B domain ͑see Fig. 10͒.…”

“…It should be noted that substantial part of the growth of the semipolar film might proceed along the ͓0001͔ direction for domain A, which will lead to great reduction in BPSF formation. 8 However, additional structural analysis is required to confirm this speculation. …”

“…1͒ have been grown on r-plane sapphire, 3 ͑100͒ ␥-LiAlO 2 , 1 a-and m-plane SiC, 4,5 and more recently on a-and m-plane GaN substrates. 6,7 Semipolar nitride films have been mostly grown by using lateral epitaxial overgrowth techniques 8 but also on m-plane sapphire, 9 Si͑001͒, 10 and semipolar GaN bulk substrates. 11,12 The structural characteristics of the nonpolar and semipolar nitride films are expected to be anisotropic as a result of the anisotropies of film and substrate surfaces.…”