My AFM images for ZnO thin films show different surface roughness at different dopants concentrations. What is the effect of the surface roughness on the optical and electrical properties of ZnO thin films?
rough surface creates charge carrier traps therefore is not good for electrical conductivity. Optical I dont know
Dear Abbas,
especially in thin films, the surface properties influence the electrical and optical properties essentially.
Lets begin with electrical properties:
The electrical and thermal conductivity depends on surface roughness - why? An electron (hole) or a phonon can be backscattered by interaction with the surface. This enhances the resistance. A resistance is nothing more than the disturbance of the periodic potential of a crystalline structure. If a charge or phonon must move back we have a momentum reversal. This means, the resistance increases. In thick layers, the interaction with the surface can be neglected, but if the mean free path l is comparabel to the thickness, the surface interaction is a dominating contribution, in metals l
Surface roughness in TCOs, such as ZnO, can strongly improve light reflection. Transparent conductive oxides with optimised roughness are in fact largely used as antireflecting front contacts in solar cells, allowing an optimal light management in the cell. See for example the works on light trapping developed by PVMD group at Delft University of Technology.
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