Schematic representation of the epitaxial relationships between wurtzite nonpolar films with R-sapphire (a) and M-sapphire (b). The sapphire axes are in white and the GaN/ZnO axes in black.
Schematic representation of structural defects in an A-oriented wurtzite film on R-sapphire. The different kinds of defects are indicated. The wurtzite axes are also shown.
(a) and (b) PV-HRTEM of BSF in a (11–20) oriented ZnO film. Burger circuits (from S to E) show that the BSF + PD groups correspond to a dissociated c-type dislocation (a) and an a+c-type dislocation (b). (c) PV-(0002) lattice images of the left (L) and right (R) edges of a BSF in a (11–20) oriented GaN film.
(a) HRTEM image of the interface between (1–100) GaN and M-sapphire along the [11–20]GaN (sapphire) zone axis. (b) Fourier transform of the image in Figure 2(a). The spots used for Fourier filtering in Figures 2(c) and 2(d) are indicated. (c) Fourier filtered image of the image in Figure 2(a) using (0002)GaN and (11–20)sapphire spots. The white arrows indicate additional planes in sapphire (MD). (d) Fourier filtered image of the image in Figure 2(a) using (1–100)GaN spot. The black lines indicate the positions of BSFs.
PV- dark field image of a thin layer (a few nanometers) of (11–20) ZnO on R-sapphire. The inset is a selected area electron diffraction pattern where the (1-100)ZnO and (11–20)sapphire spots used for imaging are shown. White arrows indicate BSFs and red arrows edge dislocations. The ZnO axes are indicated.
(a) PV-HRTEM image of a thin (a few nanometers) (11–20) ZnO on R-sapphire. The inset is the Fourier transform. (b) Fourier filtered image of the image in Figure 4(a) using the (1–100)ZnO spot. White arrows indicate BSFs.
(a) Phase image of the image in Figure 6(a) for (1–100)ZnO planes. The phase reference is in region 3. (b) Profile of the phase in the rectangle drawn in Figure 7(a), the intensities being projected along the small side of the rectangle.
(a) Schematic representation of the initial stage of the nucleation of (11–20) ZnO on R-sapphire. The sapphire (11–20) planes are represented in blue and the ZnO (1–100) planes in red. The black arrows indicate geometrical MDs. Two independent growth islands are shown. The crystalline directions of ZnO are indicated. (b) Coalescence of the two islands of Figure 8(a). The independent formation of geometrical MDs in the two islands result in a translation of the (1–100)ZnO planes.
In-plane lattice mismatches of nonpolar A-GaN and A-ZnO with R-sapphire and M-GaN with M-sapphire along the 2 main perpendicular in-plane directions. N is the distance between interfacial misfit dislocations necessary for a full relaxation. The densities of misfit dislocations (1/N) along  are also given.
Measured densities of structural defects for A-GaN6 and A-ZnO8 on R-sapphire and for M-GaN on M-sapphire (this work).
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