Electrical and Methanol Sensing Characteristics of RF Sputtered n-ZnO/p-Si Heterojunction Diodes

This paper reports structural, electrical, and gas sensing characteristics of n-ZnO/p-Si heterojunction diodes fabricated using RF sputtering technique. The microstructural and surface morphological properties have been studied using X-ray diffraction, atomic force microscopy, and scanning electron microscopy, respectively. The electrical properties of the fabricated diodes have been investigated using current-voltage (I-V) and capacitance-voltage (C-V) measurements. The estimated values for rectification ratio, ideality factor, and barrier height were found to be ~100, 3.27, and 0.72eV, respectively, at room temperature. The values recorded for carrier concentration and barrier height using C-V measurement were 3.82 × 10
¹⁴
cm
^-3
and 0.79 eV, respectively. The value of series resistance using Chueng's function was found to be 1710 Ω. After detailed structural and electrical characterization, methanol sensing response (3-100 ppm) of n-ZnO/p-Si heterojunction diodes for the temperature range of 27 °C-150 °C have also been investigated. The optimum operating temperature for methanol sensing was found to be considerably low, i.e., 100 °C. The values of response magnitude, response time and recovery time at 100 °C were estimated as 82%, ~4 and ~7 s, respectively. The cross sensitivity study for the nearest interfering species, such as ethanol, 1-propanol, butanol, butanone, and benzene, has confirmed the high selectivity of n-ZnO/p-Si heterojunction diodes for methanol sensing.