Junction Capacitance in a GaAs Photodiode

[GraemeC]

I am trying to get an estimation the junction capacitance of my GaAs Photodiode with respect to varying bias voltages.

My Semiconductor Physics online textbook gives the following equations

with
ε₀ = permittivity of free space
ε_GgAs = GaAs dielectric constant
μ = Mobility of electrons
ρ = resitivity
V_bi = built-in voltage
V_A = Bias voltage (in my case 0 - 5V)
A = photodiode area (in my case 0.3μm²)

Whenever, I work through the calculations I get answers that are many orders of magnitude off what I expect

I think the main issue is just getting the correct values(in the correct units) for each of the variables as I have been pulling them in from different sources.

Any help would appreciated.

 

[Baluncore]

Welcome to PF.
What is the make and model of the photodiode ?
What capacitance do you expect ?

 

[GraemeC]

It's custom part.
My colleague did a calculation a while back and came up 250pF at 0V
I'm getting femtoFarads which is definitely not right!

 

[marcusl]

You haven't shown us your work. You seem to have diagnosed your problem is, but haven't taken the step of fixing it. What exactly are you asking for?

 

[GraemeC]

Confirmation that the equations I've given are correct and then values for
ε0 = permittivity of free space
εGgAs = GaAs dielectric constant
μ = Mobility of electrons
ρ = resitivity
Vbi = built-in voltage