ZnO a wide direct-gap semiconductor

attracts as much attention as GaN in optoelectronics research field.Recently

there has been a great progress in the growth of ZnO thin films.But applicable ZnO optoelectronic devices have not been fabricated yet

mainly due to that sufficiently effective p-type ZnO thin films have not been obtained up to now.To solve the p-type doping problems

it is necessary to grow higher quality ZnO thin films.One of the key issues to grow high quality ZnO thin films is to find a lattice matched substrate.GaN and ZnO have close lattice constant and the mismatch of them is less than 2%

so GaN is the suitable substrate for the growth of ZnO epitaxial layers.At present

the technique of growing high quality GaN films on Al

2

O

3

substrate has developed mature through the research of more than ten years

it is a feasible method to use the GaN epilayer as the buffer layers on other substrates for the growth of ZnO epitaxial layers.ZnO films used in this study were grown by a home-built vertical atmospheric pressure MOCVD system.The GaN/Al

2

O

3

templates were fabricated by a low-pressure MOCVD system Thomas Swan

CCS.The thickness of the GaN layer was about 3 mm.We used deionized water and Zn(C

2

H

5

)

2

as the O and Zn sources

respectively

and nitrogen as the carrier gas.The thickness of the ZnO layer is 2 μm.ZnO epilayer characteristics were investigated by AFM

DCXRD and PL.XRD spectra showed that the threading dislocation density of the ZnO films is in the order of 10

8

cm

-2

which is comparable to device-level GaN films.The ZnO films showed very bright near band-edge luminescence is at 3.263 eV at room temperature and the deep-level emission is quite weak in the whole spectrum.The absence of the deep-level emission peak indicates that the ZnO films are of excellent optical quality and have few interior defects.From the low temperature PL spectrum

the domination of free exciton and the appearance of its two replicas strongly further prove the high quality of the ZnO films.This superior optical feature is an indication of the potential of atmospheric pressure MOCVD for ZnO growth on epi-GaN/Al

2

O

3

templates.