Importance of N-P-N Junction in H2S Sensing Process of SnO2-CuO Heterostructures: A Theoretical Macroscopic Approach

Metal-oxide gas sensors are widely used for detection of detrimental H
₂
S gas. Among them, SnO
₂
-CuO system has been proved to be an excellent candidate. The previous theoretical 2D thin bilayer model was able to explain some aspects of H
₂
S sensing performance of this promising system. However, experimental researches have indicated that response values for this system are very diverse and various SnO
₂
-CuO multicomponent heterostructures such as rods, wires and particles have much higher response than their thin bilayer counterparts. Understanding the reason behind this differences would help fabrication of optimized sensor element. However, the previous model cannot address this issue mainly because it doesn't consider intrinsic n-p-n junctions which exist in SnO
₂
-CuO multicomponent heterostructures. In current research, by implementing an n-p-n junction in a 3D “SnO
₂
wire/CuO shell” model, that issue has been originally addressed. For this purpose, Poisson, Laplace and Continuity equations were solved in cylindrical coordinate to obtain H
₂
S response of “mono-wire” and “two-wires” configurations. Results showed that while these two configurations have almost equal electrical resistances in presence of H
₂
S gas, the n-p-n junction makes the “two-wires” system much more resistive in air and consequently much more sensitive toward H
₂
S gas comparing to “mono-wire” and thin bilayer configurations. Depending on the geometrical parameters, response of the “two-wires” configuration changed between 4000 to 35000 at 150°C and 1ppm H
₂
S gas. Theoretical results are in part consistent with previous experimental reports.