High-Quality ZnO Layers Grown by CVD on Sapphire Substrates with an AlN Nucleation Layer

The growth of single-crystalline high-quality zinc oxide (ZnO) layers by a methane (CH4)-based chemical vapor deposition (CVD) growth process on sapphire substrates with an aluminum nitride (AlN) nucleation layer was investigated. We achieved monocrystalline ZnO layers free of rotational domains, which show in high-resolution X-ray diffraction (HRXRD) measurements a very narrow (∼110 arcsec) full width at half-maximum (fwhm) in ω scans for the ZnO (0002) reflection. The influence of growth time and layer thickness on crystal properties such as surface roughness, dislocation density, and optical properties was investigated. We find low edge and screw dislocation densities of around 6.4 × 108 and 2.1 × 107 cm–2, respectively. In low-temperature photoluminescence (PL) spectra the fwhm of the donor-bound exciton emission drops to about 170 μeV for increasing layer thickness. Moreover, these layers have a smooth surface with a surface roughness RMS value of 4 nm and a very low donor concentration of about 1.7 × 1015 cm–3. We also studied the influence of substrate miscut on crystal growth properties and found no significant influence. The results prove the high potential of methane-based chemical vapor deposition for the production of high-quality ZnO layers.