188宝金博页面版

Defect-related photoluminescence emission from annealed ZnO fi lmsdeposited on AlN substratesJijun Ding*, Haixia Chen, Haiwei FuCollege of Science, Xi’an Shiyou University, Xi’an, Shaanxi 710065, ChinaA R T I C L E I N F OArticle history:Received 10 May 2017Received in revised form 24 July 2017Accepted 26 July 2017Available online 27 July 2017Keywords:AlNZnOBlue emissionPL mechanismA B S T R A C TZnO fi lm deposited on AlN shows excellent blue emission. Photoluminescence (PL) emission is furtherenhanced by annealed treatment. The corresponding emission mechanism is discussed. V Al -O N are thedominant form of V Al in as grown AlN samples. When the energy of the incident photons is just enough topump the electrons up to the V Al -O N energy level, a mass of electrons can be directly trapped by the V Al -O N defect centers, which will induce effective transitions from these defect energy level to the top of thevalence band, and then transitions to Zn vacancies levels in ZnO due to similar lattice constants betweenZnO and AlN. The energy interval between the V Al -O N in AlN and the Zn vacancies defect states in ZnO isabout 2.96 eV, which is well consistent with the energy of the blue peak at 420 nm (2.96 eV).© 2017 Elsevier Ltd. All rights reserved.1. IntroductionZnO, with wide band gap (?3.37 eV) and large exciton bindingenergy (?60 meV), is an ideal II–VI semiconductor materials foroptoelectronic devices [1,2]. It can be applied to laser diodes,ultraviolet lasers, solar cells, thin fi lm transistors, transparentconductive contacts and emitters [3,4]. Over the past decades,there has been considerable progress in ZnO crystal growth,doping, structural design, light emission enhancement andcorresponding origin. Zeng et al. [5] investigated defect originand emission control in ZnO nanoparticles. Santangelo et al. [6]found that non-stoichiometry inf l uenced photoluminescence (PL)properties of Al- and/or Ca-added ZnO fi bers. Dhara and Giri [7]discussed the origin of enhanced PL from Au and Ti nanoparticlesdecorated ZnO heterostructures based on energy band alignment.Qiu et al. [8] studied the effect of doping and various metal contactson the switching characteristics of ZnO-based memristive devices.Chia et al. [9] reported the PL of ZnMgO alloy thin fi lms as afunction of either excitation intensity or temperature. Güder et al.[10] improved optical properties of ZnO thin fi lms by thermalannealing. Our previous results also indicated that the PL emissionof ZnO nanorods can be enhanced by coating with graphene oxidesheets [11].On the other hand, AlN is a direct band-gap III–V semiconductormaterial with the compatible thermal expansion coeff i cient withboth silicon and GaAs, high thermal conductivity, outstandingelectrical and mechanical properties, and excellent opticaltransmission [12,13]. Optical properties of AlN have also beenreported extensively. Flynn and Stewart [14] deposited AlN fi lms bymolecular beam epitaxy (MBE) under aluminum-rich conditionsand found that there are strong near-band-edge PL peaks in the as-deposited samples. Guerra et al. [15] reported the effect of Tbdoping on the PL properties of amorphous AlN thin fi lms withdifferent temperature conditions. Aleksandrov et al. [16] reportedtime-resolved and temperature-dependent PL band at 2 eV in AlNwith below bandgap excitation. Currently there are much researchinto developing its potential application for deep ultravioletoptoelectronics. In 2006, an eff i cient AlN LED emission at 210 nmwas reported [17]. Mi et al. [18] grew the AlN nanowires undernitrogen-rich conditions and investigated their applications fordeep ultraviolet light emitting diodes. Zhao and Mi [19] reviewedthe recent progress on the growth and characterization of AlNnanowires and related optoelectronic devices.Interestingly, ZnO and AlN have compatible thermal expansioncoeff i cient k and similar lattice constant c between ZnO (k = ?3.0–6.5 ?10 ?6 /K, c = 0.5206 nm) and AlN (k = ?4.2–5.3 ?10 ?6 /K,c = 0.4979 nm) [20]. At the same time, both ZnO and AlN ownindividual excellent optical properties. Combining ZnO with AlNmay give the enhanced performance. However, there are fewreports about optical properties of ZnO and AlN composites. In thispaper, ZnO fi lm is deposited on AlN substrates and sample is* Corresponding author.E-mail address: dingjj303@163.com (J. Ding).http://dx.doi.org/10.1016/j.materresbull.2017.07.0420025-5408/© 2017 Elsevier Ltd. All rights reserved.Materials Research Bulletin 95 (2017) 185–189Contents lists available at ScienceDirectMaterials Research Bulletinjournal homepage: www.else vie r.com/locat e/mat resbu