ZnO is a wide band-gap semiconductor with good electrical

optical and piezoelectric properties.ZnO has a large exciton binding energy of 60 meV

which is 2.4 times that of GaN.ZnO is extensively studied because of its potential applications in various fields

such as gas sensor

solar cells

photodetectors

light emitting diodes(LEDs) and laser systems etc.Especially

after optical pumped UV lasing of ZnO films was reported

ZnO has received more and more attention from researchers.ZnO films have been grown by many different methods

such as sputtering

molecular beam epitaxy(MBE) and metal organic chemical vapor deposition (MOCVD) and so on.Among them

MOCVD provides the advantage of growing high-quality films due to its versatility in controlling the various therm odynamic interactions.In order to obtain the high-quality ZnO films

the growth technique of using the buffer layer has been adopted in the growth process of ZnO films.However

there has been few reports on the effect of ZnO buffer layer thickness on the properties of ZnO thin films.ZnO thin films have been grown on c-axis orientated sapphire substrate with MOCVD technique.Before the growth

various pretreatments for the surface of the substrate were applied and their effects on quality of the samples were observed.By measuring X-ray diffraction of samples

we observed the effects on crystal quality of ZnO thin films after surface pretreatments.At room temperature

we investigated PL spectra of the samples by excitation of He-Cd laser at 325 nm and observed the effects of pretreating on luminescence characteristic of the samples.We tested electrical characteristic of the samples by HL 5500 Hall system.By pretreating in oxygen

the resistivity of the film increased and Hall mobility declined.On the contrary

the resistivity of the film declined and Hall mobility increased by pretreating in nitrogen.The surface morphology

the structural and optical properties of ZnO films were improved by pretreating the surfaces of the substrates.