Junction Capacitance in a GaAs Photodiode

In summary: VA = Bias voltage (in my case 0 - 5V)A = photodiode area (in my case 0.3μm2)In summary, the conversation discusses the difficulty in obtaining accurate estimations for the junction capacitance of a GaAs Photodiode at varying bias voltages. The individual is using equations from a Semiconductor Physics online textbook, but is struggling to obtain correct values for the variables, which are pulled from different sources. They are seeking confirmation on the correctness of the equations and assistance in obtaining values for the variables. The expected capacitance is around 250pF, but the individual is currently getting values in the femtoFarad range, which is incorrect.
  • #1
GraemeC
3
0
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

Junction1.PNG


with
ε0 = permittivity of free space
εGgAs = GaAs dielectric constant
μ = Mobility of electrons
ρ = resitivity
Vbi = built-in voltage
VA = 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.
 
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  • #2
Welcome to PF.
What is the make and model of the photodiode ?
What capacitance do you expect ?
 
  • #3
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!
 
  • #4
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?
 
  • #5
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
 

What is junction capacitance in a GaAs photodiode?

Junction capacitance in a GaAs photodiode refers to the capacitance that exists at the junction between the p-type and n-type semiconductor materials. It is a measure of the ability of the photodiode to store an electrical charge when a voltage is applied across the junction.

Why is junction capacitance important in a GaAs photodiode?

Junction capacitance is important in a GaAs photodiode because it affects the response time and frequency response of the device. A high junction capacitance can result in slower response time and reduced sensitivity, while a low junction capacitance can improve the device's speed and sensitivity.

How is junction capacitance measured in a GaAs photodiode?

Junction capacitance in a GaAs photodiode can be measured using a capacitance-voltage (C-V) measurement. This involves applying a small voltage across the junction and measuring the resulting capacitance. The C-V measurement can provide information about the doping concentration and material properties of the photodiode.

What factors affect the junction capacitance in a GaAs photodiode?

The junction capacitance in a GaAs photodiode is affected by factors such as the doping concentration, thickness of the depletion region, and the type of material used. The junction capacitance also increases with increasing reverse bias voltage and temperature.

How can the junction capacitance be reduced in a GaAs photodiode?

The junction capacitance in a GaAs photodiode can be reduced by decreasing the doping concentration, reducing the thickness of the depletion region, and using a different material with a lower dielectric constant. Additionally, applying a reverse bias voltage can also decrease the junction capacitance by widening the depletion region.

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