I currently fabricated a p-n heterojunction between 2 semiconductors.
The p-type semiconductor (nanorod, thickness of ~700 nm) was electrodeposited on n-semiconductor (bulky, thickness of 700 nm).
The electrochemical impedance spectroscopy (EIS) were conducted at 0.5 V vs. Ag/AgCl (1.23 vs. RHE) with an AC amplitude of 10 mV, frequency of 100 kHz–0.1Hz, under simulated sunlight irradiation.
My first question is why does heterojunction only appear 1 semicircle in EIS measurement instead two semicircles (See attachment)? Could anyone please give me an detailed explaination?
The second question is how do we choose equivalents circuit to fit the data?
Hi,because you have one relaxation time,and the equivalent circuit model used consists of Rs in serie with (Rp //CPE).if tou extract Z' or Z'' versus frequency in semi log scale, you will see a peak (in Z'') which corresponds to the inflexion point of Z'. from this peak you can calculate the relaxation time and determine the relaxation type (Maxwell Wagner for example).
in the case of 2 semicircles, you have to add another circuit element to fit the scond semi circle observed.
- in order to choose the best model, we have to begins with the simple circuit, if the fit is not good you add other element to your circuit.
you can see this paper: DOI: 10.1016/j.jpcs.2017.03.011
good luck
Generally speaking, there are several reasons, why two processes could generate only one semicircle in the Nyquist plot. For example:
1. The time constant of the processes are the same or similar. Then two semicircles will merge to one and there is no (mathematical) way to separate them, neither in the Nyquist plot or any other diagram, if you have only this measurement.
2. One of the processes is much larger than the other. Then the smaller one might be difficult to detect.
- Badges
- Science topic
- Similar topics
- Chemistry
- Electrochemistry