Structural and photoluminescence characteristics of ZnO films by room temperature sputtering and rapid thermal annealing process

Abstract

Zinc oxide (ZnO) is a wide band gap semiconductor with band gap of 3.3eV and attracts much interest in its luminescence characteristic. As literatures reported, the ultraviolet and visible light emissions of ZnO films are caused by band-to-band transition and deep level emission, respectively. The deep level emission was believed to be caused by the intrinsic defects such as oxygen vacancies and zinc interstitial.In this study, ZnO films were successfully deposited on SiO 2 /Si substrates at room temperature (RT) and annealed at ambient atmosphere from 200к to 900к.From the X-ray diffraction (XRD) patterns, the (002) peak were found to be the dominated peak of ZnO thin films annealed from 200к to 900к. However, there exists a Zn (101) peak located at 2Ӱ=43.175̓ as the films were annealed from 200к to 500к and it disappears as the annealing temperature is above 600к. The scanning electron microscopy (SEM) analysis shows that the grain seems small as the annealing temperature is within 200к to 400к and becomes larger as the annealing temperature reaches 500 к . The grain boundaries are not clear and the grain represents a melting status from 500к to 700к. The grain boundaries are apparent as the temperature attains to 900к. The structural transformation of ZnO films annealed at 400к and 500к might be considered as the bonding formation of the melting zinc atoms with oxygen atoms because the melting point of zinc is around 420 к . According to the PL measurement shown in Fig. 1, the characteristic ultraviolet (UV) luminescence located at 375nm appeared and became stronger as the annealing temperature increased from 200к to 500к. As the annealing temperature was kept increasing upto 600к, the UV emission intensity was lower down and the green light emission appeared. As the annealing temperatures were increased from 600к to 900к, the UV emission intensity became weaker and the green emission intensity was stronger. The strongest visible emission appeared when ZnO film was annealed at 900к. 849 0-7803-9217-5/05/$20.00©2005 IEEE

Ultraviolet photoluminescence of ZnO quantum dots sputtered at room-temperature

“…It is deposited at room-temperature, but annealed for 3 h at 500 • C in 5 sccm O 2 and 20 sccm N 2 . Similiar thin-film preparation procedures, involving annealing steps between 400 • C and 600 • C, have been reported earlier to result in strong UV emission between 3.27 eV and 3.31 eV and suppression of defect photoluminescence in bulk ZnO [9,10,11]. Evaluation of the optical transmittance (not shown) of the 330 nm ZnO layer results in a bandgap of E bulk g = 3.28(1) eV.…”