Realization of CO2 gas sensors and broadband photodetectors using metal/high-k CeO2/p-Si heterojunction

Abstract

Realization of high-k dielectric oxide material-based devices such as photodetectors (PDs)/gas sensors fabricated on silicon substrate seems to be the utmost promising as a cost-effective approach to use in next generation optoelectronic field. We have explored metal/CeO2/p-Si heterojunction to construct as a broadband (BB) PD and CO2 gas sensor device. The effect of post-annealing procedure on photodetection and CO2 gas sensing characteristics were correlated using AFM, XRD, XPS, Raman and UV–Vis studies. At 0 V bias, the fabricated as-deposited Au/CeO2/p-Si PD device exhibits outstanding performance with enhanced responsivity of 85 AW−1 (at 910 nm), detectivity of 1.36×1015 Jones (at 850 nm), EQE of 1.3×104 % (at 850 nm), faster rise and fall times of 124 ms and 107 ms (at 900 nm). On the other hand, the photodetection characteristic parameters were slightly deteriorated as a function of annealing with respect to the as-deposited device. One of the causes for this fact was attributed to the increase in rms surface roughness (AFM) and decrease in absorbance of CeO2 thin film (UV–Vis). Additionally, Ag/CeO2/p-Si heterojunction was studied as a CO2 gas sensor and evaluated response/recovery times as a function of CO2 gas concentration. Sensing responses of CeO2 as-deposited, CeO2-400, CeO2-500, CeO2-600 and CeO2-700 °C were around 58, 60, 62, 81 and 90 %, respectively, when exposed to 200 ppm of CO2. Thus, we validate that the prospect of integrating enhanced performance in BB PDs and CO2 gas sensors using metal/CeO2/p-Si heterojunction could serve as a basic building block in near future optoelectronic applications. Furthermore, the effect of post-annealing temperature on the morphological, structural, BB photodetection and CO2 gas sensing properties were discussed in detail.