Zener diode behavior of nitrogen-doped graphene quantum dots

Nitrogen-doped highly fluorescent graphene quantum dots (N-GQDs) were synthesized, using ammonia as nitrogen and d-glucose as carbon source, using a facile microwave-assisted protocol, where the N/C ratio could be varied from 0.19 to 0.25 (% w/w, determined from EDAX). The as-synthesized quantum dots consisting of one to three graphene monolayers exhibited high crystalline morphology with an average size of 1.8 ± 0.2 nm. HRTEM data showed the presence of both pyridinic-N and pyrrolic-N structures. Semiconductor profile of the N-GQDs was extensively probed, and it was noticed that the optical bandgap, knee-voltage and break-down voltage varied linearly with the N/C ratio. The doped samples showed with an optical bandgap ≈5.3 eV at the maximum nitrogen doping yielding n-type semiconductor property. Clear Zener diode attributes with a large forward bias current (100-200 mA), and a smaller reverse bias current of typically half that value was found.