Current Transport in Al-Diffused ZnO/Si Heterostructures

The current–voltage–temperature (I-V-T) characteristics of transparent Al-doped ZnO (AZO) on n-Si heterojunction structures were analyzed with respect to two different Al diffusion temperatures, 200°C and 600°C. Thin films of Al were deposited on top of the ZnO/Si structures, followed by introducing the Al atoms into the ZnO to form AZO through a process of thermal diffusion. Measurements at temperatures of 150–400 K were carried out in order to understand the temperature dependence of the heterostructure diode characteristics for photovoltaic applications. The results indicated the difference in current mechanisms observed in the two diodes with different Al-diffusion temperatures and Al thicknesses. The charge transport mechanism in the 200°C diodes indicated thermionic field emission (TFE) as the dominating mechanism, whereas the 600°C diodes resulted in field emission (FE) as the dominating current transport. The differences in conduction mechanisms explain the better solar cell performance using the 200°C process.