Low-macroscopic field emission from nanocrystalline Al doped SnO2 thin films synthesized by sol-gel technique

We have observed low-macroscopic field electron emission from wide bandgap nanocrystalline Al doped SnO2 thin films deposited on glass substrates. The emission properties have been studied for different anode-sample spacings and for different Al concentrations in the films. The turn-on field and approximate work function were calculated and we have tried to explain the emission mechanism from this. The turn-on field was found to vary in the range 5.6-7.5 V/mu m for a variation of anode sample spacing from 80-120 mu m. The turn-on field was also found to vary from 4.6-5.68 V/mu m for a fixed anode-sample separation of 80 mu m with a variation of Al concentration in the films 8.16-2.31%. The Al concentrations in the films have been measured by energy dispersive X-ray analysis. Optical transmittance measurement of the films showed a high transparency with a direct bandgap similar to 3.98 eV. Due to the wide bandgap, the electron affinity of the film decreased. This, along with the nanocrystalline nature of the films, enhanced the field emission properties.