Hello,
I have been working on Au/n-GaAs (Si doped) Schottky junctions. It is very well know that dark reverse saturation current (J0) is primarily dependent on temperature and nothing else (in ideal case I assume!).
However, I can clearly see a doping concentration dependence on my experimental results, which I cannot figure out. It is observed that J0 is usually 100-1000 times smaller for doping concentration of 10^16 cm-3 than 10^17 cm-3.
Can anyone explain this?
Thanks,
Amir
Dear Amirhossein,
welcome,
I would like to add to Abu Kowsar that the dependence of the dark reverse situation current of your device on the doping concentration points out that barrier height at the interface is affected by the presence of surface state at the interface at the surface of semiconductor, here GaAS.
In case that the barrier height is dominated by the surface states such that there is Fermi level pinning at the surface, then the barrier height phi from the metal to the semiconductor can be expressed by:
phi = Eg- phi0 , where Eg is the energy gap and pho is the level of the surface state which is pinned to Fermi level. For lower doping concentration , phi0 will be lower and the barrier height increases leading to larger barrier height and consequently much smaller reverse current. This may explain your observation.
For more details you may refer to S MSze, physics of semicondcutor devices.
Best wishes
Dear Mr. Amir,
Dark saturation current decreases with the increase of the doping concentration.
Please see the attachment, where you can find the relationship between the Dark current ( Reverse saturation current density and donar/accepter concentration).
Dear Amirhossein,
welcome,
I would like to add to Abu Kowsar that the dependence of the dark reverse situation current of your device on the doping concentration points out that barrier height at the interface is affected by the presence of surface state at the interface at the surface of semiconductor, here GaAS.
In case that the barrier height is dominated by the surface states such that there is Fermi level pinning at the surface, then the barrier height phi from the metal to the semiconductor can be expressed by:
phi = Eg- phi0 , where Eg is the energy gap and pho is the level of the surface state which is pinned to Fermi level. For lower doping concentration , phi0 will be lower and the barrier height increases leading to larger barrier height and consequently much smaller reverse current. This may explain your observation.
For more details you may refer to S MSze, physics of semicondcutor devices.
Best wishes
In addition to the above, doping concentration also affects the WIDTH of the barrier -- larger ND will make the barrier thinner and thus enable tunneling of charge carriers through it. Tunneling currents have a specific exponential voltage dependence and also do not depend on temperature, which you can easily check.
Thank you everyone for the contribution. I did some basic calculation, and found out that the barrier height lowering has a significant effect on the dark reverse current and the experimental results are in good match with what was calculated. If anyone is interested to find the formulas related to barrier lowering and related materials to it, check out the following link:
https://ecee.colorado.edu/~bart/book/book/chapter3/ch3_3.htm
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