I am working on dilute nitride solar cells. Our cell structure is double p-i-n heterojunction. I have done C-V analysis on it at a different frequency (100 Hz -1 MHz) with10 mV ac voltage. The Mott-Schottky analysis shows negative built-in potential. I am completely lost how to address this negative built-in potential. What does negative built-in potential signify? Has anybody had any experience or idea about this? Please see the attached solar cell structure, C-V, and Mott-Schottky plots.
Non-ideal (including interface states) assessment of MIS interface formation involves one macroscopic dipole and two microscopic dipoles. The negative macroscopic dipole gives rise to a negative built-in potential that is dropped across the insulator and the semiconductor depletion layer. The negative microscopic dipole present at the metal-insulator interface reduces the barrier for electron injection from the metal into the insulator while the positive microscopic dipole at the insulator-semiconductor interface increases band bending in the semiconductor and also increases the barrier for electron injection from the semiconductor into the insulator.
Owing to the consistency of IV and VL plots for different devices, we can state that devices fabricated to be identical have known characteristics, and display consistent behaviour under illumination and under no illumination, and also upon application of a magnetic field during measurements. Deviation from that behaviour could indicate a problem with the system set-up or a fault in the measuring equipment. For example, between 0V and the built in voltage, the photogenerated current increases from a negative current to zero current. The quantity of charge carriers within the device does not change with increasing voltage. This reduction in null field current causes an increase in the magnitude of MR data with increasing voltage up to the built in potential, producing some fairly typical data sets for different diodes.
Hoping this may be useful...
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