Investigation of a p-CuO/n-ZnO thin film heterojunction for H₂gas-sensor applications

Abstract

A p-CuO/n-ZnO thin film heterojunction is fabricated on a glass substrate by the sol-gel technique. The crystallinity of the junction materials and microstructure of the top p-layer are examined by an x-ray diffractometer (XRD) and scanning electron microscope (SEM). The current-voltage (I-V) characteristics of the p-n heterojunction and its temperature dependence have been investigated in air and H 2 ambient. Although the junction possesses linear I-V characteristics from room temperature (RT) to 150 • C in air, at higher temperatures (200 • C to 300 • C), it shows nonlinear rectifying behaviour. The forward current is greatly increased with increasing temperature while the reverse current is increased slightly resulting in a I F /I R ratio as high as 485. The ideality factor (n) is 4.88 at a temperature of 300 • C. The forward current is highly increased by the introduction of H 2 gas at 300 • C. However, a simultaneous increase in the reverse current makes the I F /I R ratio 8.4. It is observed that H 2 sensitivity of the heterojunction is increased with the increase in temperature as well as the thickness of CuO film. A sensitivity value as high as 266.5 is observed at 300 • C when biased at 3 V in the presence of approximately 3000 ppm of H 2 .

Optical and current transport properties of CuO/ZnO nanocoral p–n heterostructure hydrothermally synthesized at low temperature

“…So far no reports on CuO/ZnO heterojunctions that were achieved by direct growth of CuO NSs on ZnO NRs have been demonstrated. Recently, few attempts of growing CuO/ZnO composites were performed [27][28][29][30]. For these composites either high temperature or expensive UV growth procedures were used.…”

A facile one-step synthesis of p-CuO/n-ZnO nanowire heterojunctions by thermal oxidation route

“…There into, cupric oxide (CuO) is an important p-type transition metal oxide semiconductor that shows photoconductivity, photovoltaic properties, field emission, and electrochemical and catalytic properties (narrow energy gap of about 1.2 eV and conductivities of 10 À 4 S cm À 1 ) [4,5]. And zinc oxide (ZnO) is one of the most promising n-type semiconductor materials due to its superior electrical, piezoelectric and optoelectronic properties (energy gap of about 3.37 eV and conductivities of about 10 À 7 -10 À 3 S cm À 1 ) [5,6]. The holes of the valance band from p-CuO are the majority carrier in the conductive process, and for n-ZnO, the excited electrons participate the process of conduction.…”

UV Illumination Room-Temperature ZnO Nanoparticle Ethanol Gas Sensors

“…Semiconducting metal oxide sensors have been widely studied because of their small dimensions, low cost, and high compatibility with microelectronics. ZnO gas sensors of various forms, such as thick films [17], thin films [18], heterojunctions [19], nanoparticles [20], and nanotubes [21], have all been demonstrated. The oxygen-related gas-sensing mechanism involves the absorption of oxygen molecules on the oxide surface to generate chemisorbed oxygen species (O 2 − , O 2− , O − ) by capturing electrons from the conductance band, making the oxide surface highly resistive.…”