The structure of unintentionally doped GaN grown by organometallic vapor phase epitaxy on Al

2

O

3

substrates was investigated using Rutherford Backscattering and Ion Channeling measurements.The growth of unintentionally doped GaN films was performed by MOCVD method using a home-made vertical reactor operating at atmospheric pressure.The grwoth was carried out on(0001)oriented sapphire substrates using Trimethylgallium(TMGa)and blue-ammonia(NH

3

)as Ga and N sources

respectively.The mixed gases of hydrogen and nitropen were used as the damer gases.A thin buffer layer with thickness of about 15um was grown at 520t and recrystallized at 1060℃ for 6 minutes.The GaN films were grown at 1060℃.Rutherfold Backscattering and Channeling spectra were measured with 2.0meV He

+

ions at a scattering angle of 165°.The ion channeling minimum yields in the near-surface region(the ratio of the backscattered yield along the random direction to that of the aligned

X

min

)for four samples were 1.43%

2.13%

2.22% and 29.8%

respectively.The electrical properties of those films were measured by Van der Pauw Hall method

and their compensation ratio were 0.45

0.6

0.83 and 0.9

respectively.The results indicats that there existed some relationship between

X

min

and the compensation ratio

and the relation was unambiguous for thin films.The value of

X

min

was small in GaN with light compensation ratio

while it was large in GaN with heavy compensation ratio

but the growth in value Of

X

min

with increasing of compensation ratios was seen to be nonlinear.The experimental results were analyzed as following: high compensation suggested that there were many acceptor impurities or defects in epitaxial films of GaN.When those acceptor impurities or defects were interstitial

the incident He

+

ions would endure great scattering so that the channeled yields would increase remarkably.But as for thick epitaxial film

most part of defects were located near the interface between film and substrate

so it was possible that the crystalline quality near the film surface would be improved.In this case

the growth of compensation didn’tresult in alarge increment of

X

min

.However

in the thin films with heavy compensation

some cases were different.The acceptor impurities or defects were to be distributed over the whole epitaxial film

and near surface there still existed many impurites or defects

therefore

the value of

X

min

would increase greatly.