A Monte Carlo simulation of ballistic transport in nanocrystalline silicon diode

Abstract

Nanocrystalline silicon (nc-Si) diodes, composed of thin Au films, structure controlled nc-Si layers, n-type Si substrates, and ohmic back contacts, efficiently emit ballistic electrons when positive bias voltages are applied to the Au electrode with respect to the substrate. In this study, the characteristics of ballistic electron transport in nc-Si diodes are investigated using the Monte Carlo simulation. Both the calculated and measured energy distributions are far from that expected from the thermal equilibrium condition. We can see that a good agreement between two results is obtained on the higher energy side relating to quasi-ballistic and ballistic transport. The ballistic behavior is evident from the peaks of two distributions that correspond to 70-80% of the applied voltage. This is an indication that very few collisions occur in the higher energy region in nc-Si layer. We compared the characteristics of electron transport in nc-Si layer to that of electron transport in the superlattice structure in order to investigate the effects of the electric field in the ballistic transport in the nc-Si layer. The electrons injected into the nc-Si layer are preferentially conducted to the interfaces between nanocrystallites as into drain by a concentrated electric field. The effective thickness of the barrier at the interstice significant decreases, so the probability of sequential tunneling in nc-Si layer becomes larger than that in the superlattice. The energy distributions of electrons in the superlattice are relatively broad because the probability of tunneling is lower than that in nc-Si. The ballistic electron transport by geometry-sensitive like multiple tunneling in the interconnected nc-Si system is shown in this study. These results support that electrons can travel ballistically in nanocrystalline layers under a high electric field. The ballistic transport indicates the further technological potential of silicon nanocrystallites.