Abstract
We report on the structural properties of ZnO films grown on (001) Si, (001) GaAs, (0001) Al 2 O 3 substrates and a (0001) GaN template by RF-sputtering. It is observed that all the ZnO films have textured structures with a preferred orientation of the c-axis, irrespective growth conditions, in terms of atomic-force microscope and wide-range X-ray diffractometer. However, it is found that the ZnO films in the ZnO-on-Si and ZnO-on-GaAs are consisted of various domains with different orientations, while the ZnO films in the ZnO-on-Al 2 O 3 and ZnO-on-GaN are consisted of a single domain with the same orientation in terms of the φ-scan of X-ray diffractometer. Moreover, it is found that the ZnO-on-GaN has smaller edge dislocation density and screw dislocation density than the ZnO-on-Al 2 O 3 , which seriously depends on substrate temperature, in terms of the ω-scan of X-ray diffractometer.
Highlights
ZnO has attracted an attention as one of the promising materials required to realize the emitters and detectors in the ultraviolet region and the high-speed devices in the information communication system, because it has the outstanding physical properties of a wide-bandgap of 3.37 eV, an exiton-binding energy of 60 meV, a saturation velocity of 3.1u107 cm/sec, and a cohesive energy of 1.89 eV [1,2,3]
All the ZnO films commonly have the similar surface morphology composed of nano-sized grains, which indicates a typical evidence of textured growth, though their details are dependent on each substrate
It is reported that the ZnO film with a preferred orientation of the c-axis has the textured surface, which has the nano-scaled surface structures of various pyramidal shapes due to the columnar growth along an axial direction [11,12]
Summary
ZnO has attracted an attention as one of the promising materials required to realize the emitters and detectors in the ultraviolet region and the high-speed devices in the information communication system, because it has the outstanding physical properties of a wide-bandgap of 3.37 eV, an exiton-binding energy of 60 meV, a saturation velocity of 3.1u107 cm/sec, and a cohesive energy of 1.89 eV [1,2,3]. The ZnO film of a wurzite structure is generally grown on the (0001) Al2O3 substrate of a corundum structure, which is the most developed substrate among the materials with the similar crystalline structure to ZnO. The GaN template, which is fabricated on the Al2O3 substrate by metal-organic chemical-vapor deposition (MOCVD), with the same crystalline structure as ZnO effectively can suppress the structural defects in the subsequently grown ZnO film, because the GaN lattice has a very small lattice mismatch of 1.8 % with the ZnO lattice. We have a comparative study about the structural properties in the surface and bulk of the ZnO films grown on Si, GaAs, and Al2O3 substrates and a GaN template by using RF-sputtering
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