Abstract
A heterojunction of ZnO/porous GaN (ZnO/PGAN) was fabricated and directly applied to a diode-type humidity sensor. ZnO disks were loaded onto PGAN using a spraying process. The structure and surface morphology of the ZnO/PGAN were characterized using X-ray diffraction and scanning electron microscopy. The heterojunction displayed an excellent diode nature, which was investigated using photoluminescence spectra and I–V characteristics. The excellent transport capability of ZnO/PGAN contributes to enhanced electron transfer, and hence results in high sensitivity and quick response/recovery properties under different relative humidity (RH) levels. In the range of 12–96% RH, a fast sensing response time as low as 7 s and a recovery time of 13 s can be achieved. The simple design of a ZnO/PGAN based humidity sensor highlights its potential in various applications.
Highlights
IntroductionGaN (PGAN) can be used as an alternative material for humidity sensors
Humidity sensors (HSs) for detecting relative humidity (RH) have attracted more and more attention because of their extensive practical and potential application in industrial process control, medicine and food production, human health and environmental protection, and so on.[1,2,3,4] In the past few years, semiconducting metal oxides have been considered promising candidates for gas-sensing applications because of their high sensitivity, easy fabrication methods and low cost.[5]
The SEM images of the well dispersed zinc oxide (ZnO) disks and the surface of the ZnO/PGAN device are displayed in Fig. 3(a and b)
Summary
GaN (PGAN) can be used as an alternative material for humidity sensors The interest in this material is mainly due to its high surface to volume ratio, super chemical stability and wide direct bandgap.[14] More importantly, PGAN serving as a substrate[15] supports the sensing materials, and improves sensing performance because of its high electron mobility. A HS based on a ZnO/PGAN heterojunction as the performance-enhancement sensing layer is demonstrated, which exhibits high response and fast response and recovery time over a wide range of RH levels. A possible charge transport mechanism based on physisorbed and chemisorbed water layers is proposed to explain the measured humidity sensing response at room temperature
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