Influence of buffer layer on nitrogen doped AZO relative humidity sensor with p-n heterojunction structure

A nitrogen doped AlZnO (N-doped AZO) relative humidity (RH) sensing p-n heterojunction structure on n-type silicon substrate using DC sputtering system and lift-off technique has been proposed in this research. N-doped AZO RH sensing film was adopted to enhance photocatalyst effect and realize the heterojunction structure in humidity sensing device. The carrier properties of N-doped AZO RH sensing film were evaluated in the carrier type, carrier mobility, carrier concentration, and carrier conductivity using Hall effect measurement. The N-doped AZO RH sensors were designed with a p-n heterojunction structure and embedded a buffer layer structure. The sensing properties of N-doped AZO RH sensors both with polymer buffer layer and without polymer buffer layer were respectively explored and evaluated in the hysteresis effect, sensitivity, linearity, sensing response and recover response characteristics using environment measurement system and measurement firmware. The research results revealed the carrier type, carrier mobility, carrier concentration, and carrier resistivity of the N-doped AZO RH sensing film deposited on p-n heterojunction structure with buffer layer respectively reached as p-type, 9.6.10(1) cm(2)/Vs, 3.3.10(17) cm(-3), and 5.0x10(0) Omega-cm. The RH sensing hysteresis error of N-doped AZO RH sensor with buffer layer is approximately 4.57% at 60 %RH which is less than those at other relative humidity values. The sensitivity of N-doped AZO RH sensor with buffer layer reaches as more than 15.7 k Omega/%RH at desorption process which is better than that of sensor without buffer layer either at relative humidity value from 30 %RH to 90 %RH and from 30 %RH to 75 %RH. The adsorption linearity and desorption linearity of N-doped AZO RH sensor with buffer layer are respectively 0.31 and 0.27 between 30 %RH and 75 %RH which are better than those without buffer layer. The adsorption time and desorption time responses of N-doped AZO RH sensor with buffer layer measured during the measurement time of 2000 s with two measuring cycles were estimated about 235 s and 295 s at first cycle respectively less than those of the RH sensor without buffer layer. The design of polymer buffer layer embedded between N-doped AZO RH sensing p-n heterojunction structure and use of n-type silicon substrate revealed the better sensing characteristics and electrical properties both the molecular adsorption/desorption effects in chemical property and the carrier transport phenomena in physical property respectively.