Zinc oxide(ZnO)is a wide gap semiconductor with band gap of 3.37 eV and binding energy of 60 meV at RT.This material was expected for ultraviolet emissive device related to exciton effect at RT.For fabrication of high-quality ZnO thin films

most effort was performed.Previous work

including selected lattice match substrate(GaN

bulk ZnO or ScAlMgO

4

)

employed buffer layer(MgO)

annealing at high temperature

was successfully made to obtain high-quality ZnO thin films.In this paper

we chose c-plane sapphire(Al

2

O

3

)as a substrate of ZnO thin film.At the optimum temperature

the high-quality ZnO thin films were fabricated.During growth process

the high pure Zn source(6N)was evaporated at 245℃ by Knudsen cell and oxygen was cracked by an rf plasma atomic source(13.56 MHz).Both basal pressures of Zn and oxygen were fixed at 5×10

-5

and 3×10

-3

Pa

respectively.The chemical cleaned substrate was transferred into growth chamber and then was exposed in plasma oxygen atmosphere at 650℃.Reflection high-energy electronic diffraction pattern indicates that flat substrate surfaces appear after plasma oxygen treatment.The ZnO thin films were grown at selected temperature of 650℃.The as-grown sample was further investigated by X-ray rocking curve(XRC)

photoluminescence

and Hall effect measure.ZnO single crystal thin films were prepared on

c

-plane Al

2

O

3

substrate by plasma-assisted molecular beam epitaxy(P-MBE).A flat surface of the sample was obtained by the monitoring of reflection high-energy electron diffraction.The full width at half maximum of ZnO(002)rocking curve is 0.2°

this indicates that the sample is single crysal thin films.From photoluminescence spectrum at room temperature

an intense free exciton emission located at 3.30 eV was observed and no deep level emission appeared in visible region.Absorption spectrum shows the evident absorption peak of free exciton located at 3.36 eV.Carrier concentration of the sample is 7×10

16

cm

-3

measured by Van De pauw method.This result corresponds with the reported carrier concentration in ZnO bulk crystal.The above results indicate that the high quality ZnO single crystal thin film was obtained.