Photoelectron Spectroscopy Characterization and Computational Modeling of Gadolinium Nitride Thin Films Synthesized by C
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Photoelectron Spectroscopy Characterization and Computational Modeling of Gadolinium Nitride Thin Films Synthesized by Chemical Vapor Deposition Zane C. Gernhart1, Juan A. Colón Santana2, Lu Wang3, Wai-Ning Mei3, and Chin Li Cheung1 1
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE, 68588, U.S.A. Department of Physics, Northern Illinois University, DeKalb, IL 60115, U.S.A. 3 Department of Physics, University of Nebraska at Omaha, Omaha, NE, 68182, U.S.A. 2
ABSTRACT Here we report our study of the electronic properties of [100]-textured gadolinium nitride (GdN) thin films synthesized using a chemical vapor deposition (CVD) method. The electronic properties of the films were investigated using photoemission and inverse photoemission spectroscopy coupled with computational modeling. Our density functional theory (DFT) calculations suggest that the theoretically predicted half-metallic electronic structure of GdN is likely due to its low density of states (DOS) at the Fermi level. These calculations are supported by our photoemission and inverse photoemission spectroscopic measurements which show a band gap for the prepared films of a few milli-electron volts, seemingly consistent with the predicted electronic structure. Additionally, the use of a CVD gallium nitride capping layer was found to decelerate the surface oxidation of our GdN samples. INTRODUCTION The quest for magnetic dilute semiconductor materials for spintronic devices has led to studies of many unusual materials [1-4]. Among these, gadolinium nitride (GdN) has received a great deal of attention in this regard due to its predicted ferromagnetic nature [5-10] and hypothesized half-metallic nature [10,11]. It has been predicted that the existence of half-metallic properties in GdN could lead to its use as a spin filter [11,13]. The possible incorporation of this material into semiconducting devices has also made it a material of interest for device applications [11]. Although it is known that GdN is a ferromagnetic material, the proposed semiconducting or half-metallic nature of the material has not been confirmed. While the optical band gap of GdN has been estimated using a Tauc plot method [14], a measurement of the electronic band gap has not been reported previously. The lack of experimental data verifying the electronic behavior of GdN can be attributed to difficulties associated with sample preparation [8,12,15]. The difficulty in preparing these materials is largely due to the nature of the rare-earth pnictides which are prone to oxidation [16]. This is especially prominent for GdN because exposure of a GdN film to air results in its almost complete oxidation within several minutes [5]. In order to avoid the formation of a gadolinium oxide layer, caution must be taken to avoid exposure of the sample to ambient conditions. One method to accomplish this task which has been demonstrated with much success is the use of a GaN capping layer [5]. The use of other materials to form the capping layer has also been demonstrated [14,17,18
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