Nanostructure, optical and electrical properties of p-NiO/n-Si heterojunction diodes
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Nanostructure, optical and electrical properties of p‑NiO/n‑Si heterojunction diodes Senol Kaya1 Received: 23 March 2020 / Accepted: 17 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Evolutions on structural, morphological, optical and electrical characteristics of Pt/p-NiO/n-Si/Al thin-film heterojunction diodes before and after various thermal annealing temperatures have been investigated in details. Increases in the annealing temperature improve the crystalline structures of the films, i.e., stress on the film decreases and grain size of the film increases after annealing. The surface roughness of the films enhances from 3.60 to 4.59 nm, especially after 600 °C annealing. This rise in the surface roughness is possible due to the increase in the grain size of the films which causes swelling effect after high-temperature annealing. The energy band gap of the NiO films changes from 3.43 eV to 3.34 eV after annealing temperature up to 450 °C, while it slightly increases after 600 °C annealing process. These observed variations on the band gap values are due to the changes on the crystalline, microstructure and interfacial parameters of the films. On the other hand, the surface modifications also affect the electrical characteristics of the heterojunction diodes. The lowest sheet resistance is obtained to be 65.2 Ω/sq after 450 °C annealing process. Reverse saturation current increases up to 34.1 nA and barrier height also decreases from 0.82 eV to 0.75 eV depending on the annealing temperature. In addition, the lowest value of the ideality factor is obtained to be 1.51 for the diodes annealed at 450 °C. It can be concluded that the annealing-induced surface modifications significantly affect the electrical performance of the diodes and the optimum annealing temperature is 450 °C for the heterojunction diode applications of the p-NiO/n-Si films. Keywords Heterojunction · p-NiO/n-Si diodes · Annealing · Band gap · Thin film
1 Introduction Nickel oxide (NiO) is a wide band gap semiconductor material having controllable wide band gap of 3.4 − 3.8 eV and exhibits p-type conductivity with high optical transmittance in the visible spectra [1–4]. The p-type conductivity of NiO is associated with neutral non-stoichiometric defects such as Ni vacancies and O interstitials in the material structure. Moreover, NiO is an antiferromagnetic transition metal oxide semiconductor with excellent electrochemical stability [2, 5]. Owing to these interesting features, it has gained great interest in different technological areas such as hole-selective contact in solar cells [6], magnetic recording, [7] and gas sensing applications [8], etc. The parameters including the crystallinity, morphology and surface of nanostructures
significantly influence the magnetic/electronic performance of the materials. In particular, the rectifying behavior and possible usage in the diode applications may significantly vary depending on the diode parameters that are directly affected by fabrication process. Islam et al
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