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

Abstract

The growth of single-crystalline high-quality zinc oxide (ZnO) layers by a methane (CH 4 )-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 halfmaximum (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 × 10 8 and 2.1 × 10 7 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 × 10 15 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.

Epitaxial ZnO Layer Growth on Si(111) Substrates with an Intermediate AlN Nucleation Layer by Methane-Based Chemical Vapor Deposition

“…Most likely these impurities were not transferred to the substrate, as the use of a more pure source material did not affect the final crystal purity. Therefore, we obtained extremely low background doping concentrations for our ZnO layers, as previously reported . A recent secondary ion mass spectrometry (SIMS) measurement on equivalent ZnO layers grown on a sapphire substrate confirmed the extremely low background doping concentration: namely, for the most common donors aluminum (2.2 × 10 15 cm –3 ) and gallium (1.9 × 10 14 cm –3 ) and the most common acceptors iron (1.8 × 10 14 cm –3 ) and lithium (below the limit of detection, <1.5 × 10 13 cm –3 ).…”

“…In this work, we are reporting on the use of this novel growth method and the optimization of growth parameters for ZnO layer growth on Si substrates with an intermediate AlN nucleation layer. Because we achieved very good results for ZnO layer growth on a c-sapphire substrate, we transfer this empirical knowledge to the more challenging growth on a Si substrate. , …”

“…Because we achieved very good results for ZnO layer growth on a c-sapphire substrate, we transfer this empirical knowledge to the more challenging growth on a Si substrate. 24,25 ■ EXPERIMENTAL SECTION Prior to the growth experiments the natural amorphous SiO x layer was removed from the Si substrates by immersing the 2 in. Si wafers in peroxymonosulfuric acid (H 2 SO 5 ), which was produced by mixing sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ) in a 1:1 ratio.…”

“…Therefore, we obtained extremely low background doping concentrations for our ZnO layers, as previously reported. 25 A recent secondary ion mass spectrometry (SIMS) measurement on equivalent ZnO layers grown on a sapphire substrate confirmed the extremely low background doping concentration: namely, for the most common donors aluminum (2.2 × 10 15 cm −3 ) and gallium (1.9 × 10 14 cm −3 ) and the most common acceptors iron (1.8 × 10 14 cm −3 ) and lithium (below the limit of detection, <1.5 × 10 13 cm −3 ). The substrate was placed in the middle of the last heating zone, which was heated to 650 °C.…”

H2S sensing for breath analysis with Au functionalized ZnO nanowires

“…Here, we assume the ideal case in which both Schottky contacts have an identical Schottky barrier height f f c = -SB Au and contact area A. According to the thermionic emission theory [36], the saturation current I 0 for both contacts is: • [37] for ZnO grown in our setup as reported in our earlier works, and the mobility for unintentionally doped ZnO at room temperature [38].…”