3.6. Tunneling mechanism
From the current-voltage characteristics, we have observed
that the turn-on voltage of the LEDs that depended on the active
nanoparticles could be related to the bandgap of the AIZS
nanoparticles. As we tuned the bandgap of the nanoparticles by
decreasing the ratio of the content of silver and zinc, M[Ag]/M[Zn],
the band-edges may shift with an increase in the bandgap. In a
device based on such nanoparticles, this would mean a change in
internal barriers for the carriers.
Considering the fact that holes contribute to device current in
these LEDs, the barrier for hole injection from the electrode can
be determined from the current–voltage characteristics. With
the current in the devices being injection limited, the tunnelingcurrent can be described as
J ¼ ðAβ2E2=φÞexpðBφ3=2=βEÞ
Here, A and B are constants, β the field-enhancement factor, E the
electric field, and φ the barrier height. The equation reduces to ln
(J/E2
)p1/E with a factor of φ3/2 being the proportionality constant.
Plots of ln(J/E2
) versus 1/E (Fowler–Nordheim plots) for the LEDs
have been presented in Fig