C-plane sapphire

T.J. McArdle, J.O. Chu, Y. Zhu, Z. Liu, M. Krishnan, C.M. Breslin, et al., Multilayer epitaxial graphene formed by pyrolysis of polycrystalline silicon-carbide grown on c-plane sapphire substrates, Applied Physics Letters, 98 (2011) 132108. 

Fig. 7.5. High-resolution TEM cross section micrograph of a nominally undoped ZnO thin film on c-plane sapphire, PLD grown at 0.05 mbar O2 and 700°C. The SAD pattern is taken from both film and substrate area. Images by G. Wagner, Leipzig...

Figure 7.9 shows RHEED patterns obtained with 30keV electrons impinging on clean surfaces of optimized ZnO thin films grown on r-, a-, and c-plane sapphire. The azimuthal directions of the two types of RHEED images of the c-axis oriented ZnO films (on a- and c-sapphire) are [flOO] (top) and [2110] (bottom) [52]. 

Fig. 7.6. TEM cross-sections of PLD ZnO thin films grown on MgO buffered c-plane sapphire, (a) ZnO was grown at 0.016 mbar O2 and 600° C and shows decreasing density of dislocation lines from interface to surface, (b) ZnO was grown at 8 x 10 4mbar O2 and 580° C. The thickness of the MgO buffer layer is about 10 nm. Images by W. Mader, Bonn...

Fig. 7.9. RHEED images of optimized ZnO thin film surfaces on r-plane, a-plane, and c-plane sapphire, in the two azimuthal orientations (top and bottom) separated by 45° (left) or 30° (middle and right), respectively. The RHEED patterns of the a-axis textured film on r-plane sapphire (left) indicate an epitaxial and three-dimensional, island-like growth. The ZnO films on a-plane (middle) and c-plane sapphire (right) exhibit a smoother surface structure, as indicated by the streaky RHEED patterns and the observation of additional weak reflections in the top images due to 3 x 3 surface reconstruction [51]...

Fig. 7.15. Peak behavior of Hall mobility at 300 K of undoped ZnO thin films on c-plane sapphire at carrier concentrations around 3 x 1016 cm-3. For these particular growth conditions with a target-to-substrate distance of 50 mm, a low-temperature nucleation layer was used. Reprinted with permission from [51]...

Fig. 7.19. Photoluminescence spectra (2K) of PLD ZnO thin films on a-plane, c-plane, and r-plane sapphire substrates [63]. All films were grown at about 650°C and at 1.6 x 10 2 mbar oxygen pressure. The FWHM of the most intense donor bound exciton peaks D°X of the ZnO films are 1.4 meV on a-plane sapphire, 1.7 meV on c-plane sapphire, and 2.6 meV on r-plane sapphire. The spectral resolution of the PL setup was 1 meV at 3.35 eV...

Figure 7.19 shows PL spectra recorded at 2K for 2.2, 0.7, and 1.5 pm thick PLD ZnO films on a-plane, c-plane, and r-plane sapphire, respectively [63], The full widths at half maximum (FWHM) of the most intense bound exciton peaks are 1.4, 1.7, and 2.6 meV for a-, c-, and r-sapphire, respectively. The film on a-plane sapphire shows the narrowest FWHM among the films under investigation and the free A-exciton (Xa) is most clearly resolved, thus indicating best structural properties of ZnO on a-plane sapphire. The ZnO films on a- and c-plane sapphire grow c-axis textured, whereas films on r-plane sapphire grow a-axis oriented with the ZnO c-axis being in-plane, as demonstrated already in Fig. 7.4. The PL spectrum of the film on r-plane sapphire shows no phonon replica, probably due to the changed ZnO orientation.

Fig. 7.28. SNMS isotope intensity depth profile of a 9.5 pair ZnO-MgO Bragg mirror grown by PLD on c-plane sapphire. This particular Bragg structure had a maximum reflectivity of 85% at 2.3 eV photon energy [94], The single layer thicknesses obtained from UV-vis ellipsometry varied from 80-96 nm (MgO) and 41-71 nm (ZnO)...

FIGURE 1 Cross-sectional TEM image of GaN on c-plane sapphire (grown by MOCVD) taken near the [1100] zone with diffraction vector g-2g (g = 1120). Threading dislocations extend from a highly defective low temperature GaN buffer layer to the film surface. The density of threading dislocations is 1010 cm 2. The majority of dislocations are edge defects with b = <1120>. 

FIGURE 3 HREM image taken along the [1120] zone axis of GaN grown (by MBE) on c-plane sapphire. The zincblende (zb) GaN phase is found near the interface within a wurtzite GaN matrix. (From [7].)... 

Y. Chen, D. M. Bagnall, H. Koh, et al. Plasma assisted molecular beam epitaxy of ZnO on c-plane sapphire Growth and cheiracterization. J. Appl. Phys. 84 (1998) pp. 3912-3916. 

CPPs were used as seeds or templates for growing CNTs. Kami reported that treatment of [12]CPP, coated on a C-plane sapphire substrate, with ethanol gas as the carbon source under vacuum at 500 °C for 15 min afforded CNTs (Scheme 6.7) [59]. Transmission electron microscopy images and Raman spectroscopy confirmed the formation of CNTs the CNTs were distributed in diameter ranging... 

Figure 5.18 Room-temperature hole concentration of o-plane GaN grown on r-plane sapphire using AlGaN/AiN intermediate layer (red circle) and c-plane GaN grown on c-plane sapphire using low-temperature buffer layer (blue triangle) (cf. Color Plate XXVII).

Contrary to the growth of c-plane GaN on c-plane sapphire, the lattice mismatch between the substrate and the film in the case of a-plane GaN growth on r-plane sapphire is not spatially isotropic but depends on the crystal direction and respective lattice plane distances. Figure 11.3 shows the projected surface of the r-plane sapphire and the surface unit cell associated to it. On top of this, 1.5-unit cells of a-plane GaN are superimposed. This representation visualizes the relatively small lattice mismatch in [1100] direction of about... 

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