Analysis and development of electronic sensors based on metastable zinc nitrides

Abstract

Zinc nitride (Zn3N2) is an attractive material for microelectronics due to its band gap (1.23 eV), high mobility (~100 cm2/V*s), carrier density (1018-1020 cm-3), and low resistivity (10-2-10-3 Ohm*cm) [1]. Indeed, the development of thin film transistors and based on Zn3N2 has been recently reported [2,3]. Despite this progress, zinc nitride is still poorly studied because it is a metastable material, reacting with air in normal ambient conditions and experiencing a progressive oxidation that leads to a zinc oxide (ZnO) phase [4]. Therefore, the understanding and control of the exact mechanisms inducing this transformation is essential to build new devices based on this material. In this work we have analysed the oxidation of Zn3N2 layers grown by RF magnetron sputtering of a pure Zn target (99.995 %) with reactive N2 plasma (99.999 %) at room temperature. Different ex-situ oxidation processes has been tested, including air, thermal treatments under O2 gas and plasma (ranging from 300 C up to 900 C), and water. The passivation of the surface has been also studied, obtaining successful results with thin capping layers of ZnO. The phase transformation in both as-grown and passivated systems was monitored through scanning electron and atomic force microscopy (SEM, AFM), spectroscopic ellipsometry (SE), and elastic recoil detection analysis with time-of-flight telescope (ERDA-TOF) using 30 MeV I5+ ions. As a result of these data, we have developed electrical sensors on transparent solid (glass) and flexible (PEDOT) substrates, evaluating the response to air/water contact. These devices have been characterized with a probe station, measuring the resistivity change as a function of different parameters. Our results demonstrate that Zn3N2-based sensors can be potentially applied as chemical sensors of different gases or liquids containing O.