Structural, Optical, and Electrical Properties of Mo–Hf–O Thin Films with Spatially Varying Composition for Photocurrent and Gas-Sensing Applications
Cahuina Calderon, Daniel Alonso¹; Flores Tapia, John Alexander¹; Vilca-Huayhua, Carlos Adolfo²; Pacheco Salazar, David Gregorio¹; Herrera Aragón, Fermín Fidel²˒³
1 Laboratorio de Películas Delgadas y Nanomateriales, Escuela Profesional de Física, Universidad Nacional de San Agustín de Arequipa, Arequipa, Peru, 2 Núcleo de Física Aplicada, Instituto de Física, Universidade de Brasília, Brasília DF 70910-900, Brazil 3 Departamento de Ciencias, Sección Física, Pontificia Universidad Católica del Perú, Av. Universitaria 1801, Lima 15088, Peru
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Abstract
Mixed transition-metal oxides offer a versatile platform for tailoring optical and electrical properties through compositional control. In particular, molybdenum and hafnium oxides exhibit markedly different electronic and transport characteristics. Molybdenum oxides can adopt multiple oxidation states such as +2 to +6 and display semiconducting behavior, with their electrical and optical properties strongly influenced by oxygen stoichiometry and defect concentration. Hafnium oxide, in contrast, is a highly stable (characterized by its +4 oxidation state) and electrically insulating wide-band-gap oxide with a high dielectric constant, making it attractive for electronic and optoelectronic applications. The combination of these oxides therefore provides an opportunity to modulate the physical properties of mixed Mo-Hf-O thin films through composition. In this work, crystalline and amorphous Mo-Hf-O thin films with a compositional gradient were deposited by magnetron co sputtering. The local chemical composition was determined by energy-dispersive X-ray spectroscopy (EDS), while the influence of composition on the structural, optical, and electrical properties was investigated using X-ray diffraction (XRD), optical transmittance, and impedance spectroscopy. In addition, the photoresponse of the films was evaluated through photocurrent measurements, and their potential for gas-sensing applications was investigated. The results demonstrate that variations in the Mo/Hf composition strongly affect the optical response and electrical transport of the films, while also influencing their photoresponse and gas-sensing characteristics. These findings highlight the potential of amorphous Mo-Hf-O thin films as compositionally tunable materials for multifunctional optoelectronic and sensing applications.
Keywords: Mo-Hf-O thin films; amorphous oxides; compositional gradient