INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Effect of compensating acceptor doping with Ni on the gas sensing of In2O3
Autor/es:
N. BARSAN; A. PAPADOGIANNI; O. BIERWAGEN; F. SCHIPANI
Lugar:
Ferrara
Reunión:
Workshop; 8th GOSPEL Workshop: Gas sensors based on semiconducting metal oxides ? basic understanding & application fields; 2019
Institución organizadora:
University of Ferrara
Resumen:
Effect ofcompensating acceptor doping with Ni on the gas sensing of In2O3Alexandra Papadogianni1, FedericoSchipani2, Nicolae Barsan2, Oliver Bierwagen11Paul-Drude-Institut fürFestkörperelektronik,Leibniz-Institut im Forschungsverbund Berlin e.V., Berlin, Germany2Institute of Physical Chemistry,University of Tübingen, Auf der Morgenstelle 15, 72076 Tübingen, GermanyIndium oxide, In2O3, is a natively n-type transparent semiconducting oxide,which can exhibit highly conductive to semi-insulating behavior by extrinsic substitutionalimpurities at the indium site with donors such as Sn[1] andacceptors such as Mg[2] and Ni[3]. Among other well knownoxides, such as SnO2 and ZnO, In2O3 is commonlystudied for applications as the active material in conductometric gas sensors,due to its highly sensitive surface electron accumulation layer (SEAL).As a rule, the materials used for gas-sensing studies are polycrystallinedue to the accepted sensing models describing adsorption at grain boundaries, assumedto have the main impact on gas response. The conduction mechanism is rathercomplicated in this case, as a result of the several conductance contributions fromintra- and inter-grain transport, as well as transport along grain boundariesand at the surface[4]. Identifying the gas-sensing mechanisms,however, should be significantly simplified for model systems with reducedcomplexity, like single crystalline layers. These only have two electricallyparallel contributions from the bulk and the surface of the film (Fig. 1),which can be independently modulated. Fig. 1 Conductance contributions of a single-crystallineIn2O3 filmRemoving the parallel contribution of the In2O3bulk to the total film conductance and promoting the highly gas sensitive SEAL ?by either decreasing the layer thickness or depletion by compensating acceptordoping with Mg ? has been shown to increase sensitivity[5]. As analternative to Mg, which can introduce several complications to the growthprocedure, we investigate the effect of Ni on the gas sensitivity ofapproximately 600 nm thick single-crystalline In2O3 filmsgrown by plasma-assisted molecular beam epitaxy (PA-MBE) on YSZ (111)substrates.Measurements in air and under reactivation of the surfacewith UV-induced photoreduction show an increase of the sensitivity,demonstrated by the increased sensing parameter SENS=Gmax/Gminfor an oxygen-annealed unintentionally doped (UID) In2O3film in comparison to the as-grown film (Fig. 2, left). This is attributed to the reduced bulk electronconcentration due to the removal of oxygen vacancies acting as double donors.Incorporation of Ni acceptors further increase the sensitivity of the films,once the sample is oxygen-annealed and they are activated[3],according to the proposed mechanism.     Fig. 2 (left) Conductancechange upon UV-induced photoreduction and corresponding sensing parameters ofthree In2O3 films: as-grown (top), oxygen-annealed(middle), and Ni-doped and oxygen annealed (bottom)(right) Comparison ofresistance changes of the Ni-doped and UID In2O3 filmsupon exposure to different concentrations of oxidizing gases O2 andNO2 at an elevated temperature of 300°CThis can also provide an alternative explanation of the findingsof Refs. [6] and [7] showing an increase in sensitivity to NO2 ofNi-doped In2O3 films and nanostructures. DCresistance measurements performed in dry conditions are used for the evaluationof the sample response to two different oxidizing gases, O2 and NO2(Fig. 2, right). These confirm, in addition tothe higher room temperature response, the increased performance of the Ni-dopedsample at an elevated temperature of 300 °C as well. Workfunction calculations based on Kelvin probe measurements (not shown here) furtheraddress the influence of the SEAL and the bulk in the response of the sample. Theeffect of oxygen diffusion throughout the film, which is significant even atlower temperatures than 300 °C [8], needs to be considered. [1] O. Bierwagen and J. S. Speck, Phys. Status Solidi A 211, 48 (2013)[2] O. Bierwagen and J. S. Speck, Appl. Phys. Lett. 101, 102107 (2012)[3] A. Papadogianni, L. Kirste, and O. Bierwagen,Appl. Phys. Lett. 111, 262103 (2017)[4] A. Ponzoni, E. Comini, I. Concina, M.Ferroni, M. Falasconi, E. Gobbi, V. Sberveglieri, and G. Sberveglieri, Sensors 12, 17023 (2012)[5] J. Rombach, A. Papadogianni, M. Mischo, V.Cimalla, L. Kirste, O. Ambacher, T. Berthold, S. Krischok, M. Himmerlich, S.Selve, and O Bierwagen, Sens. Actuators B236, 909 (2016)[6] Q. Yang, X. Cui, J. Liu, J. Zhao, Y. Wang, Y.Gao, P. Sun,  J. Ma, and G. Lua,New J. Chem.  40,2376 (2016)[7] P. Bogdanov, M. Ivanovskaya, E. Comini, G.Faglia, and G. Sberveglieri, Sens.Actuators B 57, 153 (1999) [8] P. Agoston and K. Albe, Phys. Rev. B 84, 045311(2011)