Luminescence of Er-doped ZnO Films: Effects of Thermal Annealing and Doping Concentration
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1035-L08-12
Luminescence of Er-doped ZnO Films: Effects of Thermal Annealing and Doping Concentration Z Pan, S H Morgan, A Ueda, R Aga Jr., A Steigerwald, and R Mu Fisk University, Nashville, TN, 37208 ABSTRACT Photoluminescence (PL) of erbium-doped zinc oxide films with nano-sized grains was studied. The films were grown on silicon (100) and fused silica substrates using e-beam evaporation. The evaporating targets used were sintered pellets of ZnO and Er2O3 mixtures with two different Er concentrations. The films were subsequently annealed at 700 °C in air for an hour. PL was measured at two excitation wavelengths, 325 and 488 nm. The 325 nm is used for exciting the host semiconductor ZnO and 488 nm is used for directly exciting Er3+ ions in the 4 4 I15/2 and 4F9/2 I15/2 transitions was observed ZnO host. Strong Er3+ luminescence of 4S3/2 from annealed film with 4.0 % Er2O3 concentration using either 325 or 488 nm excitation. With 325 nm excitation, the Er3+ luminescence observed is attributed to energy transfer from the excitons in ZnO host to the Er3+ ions doped. The effective energy transfer from ZnO host to the doped Er3+ ions is an essential property for the realization of actual current-injection optoelectronic devices operating at wavelengths of Er3+ emission, for example, at 1.54 m for the erbium-doped fiber amplifier (EDFA). Our PL results indicate that thermal annealing plays an important role for optically activating the doped Er3+ ions in ZnO nano-crystalline grains of the film.
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INTRODUCTION Erbium-doped semiconductors are considered to be promising optical materials for optoelectronic devices [1-3]. Recently, ZnO has attracted increased attention as a candidate host material for Er-doping. ZnO is a wide band-gap semiconductor with an oxide phase, which is applicable to the excitation of Er3+ centers. It also has a high electric conductivity that is essential for the realization of actual current injection opto-electronic devices [4, 5]. Other notable properties of ZnO include a large exciton binding energy and a large Zn-O bond strength, which allows a high laser irradiation [6]. The Er-doped ZnO films have been fabricated using various techniques [2]. The luminescence at 1.54 m has been widely reported, while the visible luminescence from Er-doped ZnO films was much less reported. However, the properties of visible luminescence are important for light-emitting and display device applications [1-3]. In this article, we report on properties of Er-doped ZnO films grown on silicon (100) and fused silica substrates using e-beam evaporation, with the emphasis on visible luminescence. We characterized films both before and after annealing using X-ray diffraction (XRD), scanning electron microscopy (SEM), uv-visible absorption, and photoluminescence (PL). PL was measured at two excitation wavelengths, 325 nm and 488 nm. The 325 nm (above band-gap excitation) is used for exciting the ZnO host, while 488 nm is used for directly exciting the doped Er3+ ions in ZnO film to 4F7/2 level.
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