Recently

ZnO has attracted great interest for its wide band-gap (3.37 eV) and relatively large exciton binding energy (60 meV) at room temperature (RT). It has been regarded as one of the most promising candidates for the next generation of ultraviolet (UV) light emitting diodes (LEDs) and lasing devices (LDs) operating at high temperatures and in harsh environments. For the application of ZnO based optoelectronic devices

it is necessary to fabricate both n-type and p-type ZnO films. It is easy to obtain n-type ZnO because it is intrinsic electron-conduction. However

realization of stable and reproducible p-type ZnO has long been the bottle-neck of ZnO-based optoelectronic devices. So far

a variety of dopants

mainly the group-V elements such as N

P

As

and Sb

and group-I elements such as Li

Na

and K

has been used to produce p-type ZnO. Though great progress has been made in fabricating p-type ZnO and even fabricating ZnO based p-n junction light emitting devices

this challenge still represents a major problem since the light-emitting efficiency was generally very limited due to the low concentration and mobility of holes in the p-type layer. Group IA element may be useful only for producing semi-insulating ZnO instead of p-type material

because their small ionic radii make them very easy to form the interstitial site as donor impurities rather than substitute on Zn site as acceptor impurities. Group ⅴ elements were also faced with considerable difficulties for p-type ZnO doping because of problems such as its self-compensating effect

deep acceptor level

and low solubility of the acceptor dopants. In addition

the choice of dopant and growth technique remains controversial and the reliability of p-type ZnO is still under debate. Lately

argentum (Ag)

as group IB elements

was proposed to be a good acceptor candidate for producing p-type ZnO under oxygen-rich growth conditions based on first-principles calculations. Furthermore

p-type ZnO thin film has been achieved experimentally by Ag doping using pulsed laser deposition (PLD) technology at quite a narrow temperature range of 200~250℃. In this paper

Ag doped ZnO films (ZnO:Ag) were deposited on quartz glass substrates by ultrasonic spray pyrolysis (USP) technology. Zn(CH

3

COO)

2

and Ag(NO

3

)

3

aqueous solution were used as the sources of Zn and Ag

respectively. The effect of Ag doping on structural

electrical and optical properties of ZnO films were studied using X-ray diffraction (XRD)

scanning electron microscope(SEM)

Hall effect measurements

photoluminescence spectra

and transmittance spectra measurements. All the measurements were performed at room temperature. The surface of the ZnO:Ag film exhibits a smooth surface and very dense structure

no visible pores and defects over the film were observed. It is found that electrical and optical properties of the obtained ZnO:Ag thin films change dramatically due to Ag doping. The Ag doped p-type ZnO films with hole carrier concentration of 2.01×10

17

cm

-3

and Hall mobility of 0.24 cm

2

·V

-1

·s

-1

at room temperature have been successfully obtained at 550℃ reaction temperature.