On the origin of basal stacking faults in nonpolar wurtzite films epitaxially grown on sapphire substrates

Abstract

The microstructure of nonpolar heteroepitaxial wurtzite films (GaN and ZnO-based) is dominated by the presence of planar basal stacking faults (BSFs). In this paper, transmission electron microscopy studies of both GaN and ZnO nonpolar films oriented either (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) or (1-100) and grown on sapphire substrates, permit to propose and evaluate different mechanisms of BSFs formation. The main mechanism of formation of BSFs results from a Volmer Weber growth mode. The first stage of the growth is a 3D nucleation. The 3D nuclei are relaxed at least along one inplane orientation. BSFs are created in the coalescence boundaries in order to compensate translations between neighbouring islands. BSFs are well adapted to compensate in-plane translations in the case of nonpolar films. In fact, their plane is perpendicular to the substrate surface and this orientation is similar to the orientation of the coalescence boundaries. Moreover, their displacement vector has a component parallel to the translation between islands and their formation energy is low. On the other hand, in the case of the polar growth, BSFs are not adapted to compensate in-plane translation as their plane is perpendicular to the coalescence boundaries.

Luminescence associated with stacking faults in GaN

“…To improve the efficiency of GaN-based devices, various strategies are employed with the aim to reduce the high dislocation densities inherent to the heteroepitaxial growth of GaN and avoiding polarization fields which are detrimental to optical devices [2,3]. However, these growth strategies often result in the formation of stacking faults: Especially the growth of non-and semi-polar GaN layers [4][5][6][7][8] as well as epitaxial-lateral overgrowth [9][10][11][12][13][14] or the coalescence overgrowth of nanowires [15][16][17][18] are associated with the formation of basal-plane stacking faults independent of which growth technique is used. As a consequence, the emission characteristics and transport properties of the layers are changed [11,19].…”

Defects in semipolar $(1 1\bar {2}\bar {2})$ ZnO grown on (112) LaAlO3/(La,Sr)(Al,Ta)O3substrate by pulsed laser deposition

“…For nonpolar and semipolar wurtzite heteroepitaxial films, the BSF density is usually in the range of 10 5 -10 6 cm −1 . The origin of the stacking faults in nonpolar ZnO has been studied by Vennéguès et al [25]. They found that the main mechanism of formation of stacking faults is a compensation for the translation between neighboring islands during coalescence.…”

Cвойства полуполярного GaN, выращенного на подложке Si(100)

“…Изображения, снятые методом атомно-силовой микроскопией в двух перпендикулярных направлениях структуры GaN(1011)/SiC/NP-Si(100) показали, что поверхность дает выраженную асимметричную картину, причем базовая шероховатость составила ∼ 100 нм, присутствовали блоковые выступы GaN(1011) с размером до 250 нм (рис. В спектрах люминесценции полуполярных кристаллов обычно наблюдают линию при hν = 3.40−3.42 эВ, связанную с нарушениями дефектов упаковки BSF S -I 1 [7]), которая возникает при формировании " зародышей" по механизму Волмера−Вебера [13].…”