Studies on p-TiO2/n-graphene heterojunction for hydrogen detection

Abstract

Thermally oxidized p-type Si [resistivity (5–10)Ωcm and 〈100〉 orientation] with oxide thickness of 245nm was used as the substrate for the deposition of graphene by CVD. The formation of multilayer graphene (MLG) was confirmed by Raman spectroscopy. A heterojunction was fabricated by sol–gel coating of TiO2 on CVD grown graphene layer. The formation of titanium dioxide was verified by electron dispersion spectroscopy (EDS). The surfaces of TiO2, graphene as well as p-TiO2/n-graphene interface were characterized by scanning electron microscopy (SEM). Detail sensor study of the p-TiO2/n-graphene heterojunction was performed by taking two lateral catalytic metal (Pd) contacts deposited by e-beam evaporation. The response time of 16s and the corresponding recovery time of 61s were obtained for 0.5% H2 in air at 125°C. The p-TiO2/n-graphene junction showed selectivity for H2 compared to methane. The stability study was performed and it showed almost the steady results over a period of 3 days as tested by the discrete measurements. The sensing mechanism was formulated using a simplified energy band diagram.