Hello!
I'm trying to modulate the electron density in a thin layer of InGaAs highly doped (25nm, 1e19cm-3 n-doped) using field effect with a MOS-like structure, but for the moment, I can only change about 1e17cm-3 of the free electron density (Hall effect measurement) when I apply a +/-4V gate voltage.
Our computation using 1D-Poisson code '(Sneider's one) shows a much larger modulation (about 5e18cm-3). We are not sure what was not taken into account in the computation.
Is this feasible to modulate such large electron density? I'm searching in the literature but I haven't found any study about this. In MOS transistor I saw doping levels of 1e17cm-3 but not as high as what I'm studying.
Thanks!
N. LE-Tuan
From the first glance, the higher is the equilibrium density of free carriers, the shorter is the Debye screening length of the gate voltage. It might happened it's a great deal different as compared to 25 nm. Just a thought aloud.
Perhaps one should go through basic estimates using flat capacitor model.
The change in charge per area required to deplete some charge density N0 over channel depth of h is Qs = q* N0*h . Here q is elementary charge q =1.61*10^-19.
On another hand it has to match change in gate potential change (voltage) dV multiplied by capacitance per area C = e0*e/d
Here e0 = 8.89*10^-12 , e - oxide dielectric constant, d is oxide thickness.
Qs = dV *C = dV *e0*e/d = q*N0*h
It can be written as dV = q*N0*h*d /( e0*e)
Dear Tuan Nghia Le
The depth of the field effect is about equal the De Bye length LD= sqrt D Tau
D is the diffusion coefficient of the majority carrier and Tua is the dielectric relaxation time. Tau= epsilon /sigma.
sigma= q mu n0,
q is the electronic charge,
mu is the mobility of the electrons here,
n0 is the electron concentration in equilibrium.
Coming we to the modulation process, the charge accumulated at the electrode QG = C V,
QG= q A dN x where x is the thickness of the n-type material =25 nm
therefore average dN= CV/ q A x,
As C increases you can increase the modulation density dN .
So, please use the above formulas to calculate average dN
and report to us.
Best wishes
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