Calculating Reverse Bias Voltage for Alpha Particle Detection

In summary, the conversation discusses the calculation of reverse bias voltage required to create a depletion region in a silicon p-n detector when an alpha particle strikes it. The equation used is d= (\frac{2 \epsilon V}{e N})^{\frac{1}{2}}, and the conversation highlights the importance of using the correct units and values for each variable. It also mentions that the equation is an approximation and may not match the actual voltage required in a real experiment.
  • #1
neural_jam
18
0
Hi all, me again! :rolleyes:

I'm trying to calculate the current created when an alpha particle strikes a silicon p-n detector, but I'm getting some strange numbers, so I was wondering if I was doing something fundamentally wrong...

My problems start when I try to calculate the reverse bias voltage required to create a depletion region equal to the range of alpha particles in Si, which I understand to be 7.29x10-5m.

I use the following equation:

d= [itex](\frac{2 \epsilon V}{e N})^{\frac{1}{2}}[/itex]

where d is the depletion region (m) = 7.29x10-5
ε is the ionisation energy of Si @ 300K (eV) = 3.62
e is the charge on an electron (C) = 1.602x10-19
N is the charge carrier number density (m-3) = 1019
and V is the bias voltage.

rearranging I get

V = [itex]\frac{d^{2}eN}{2\epsilon}[/itex]

So far, so simple.

However, for some reason, after plugging the numbers in I get ~1.18x10-9V for the bias voltage, which seems to be very small :confused:

So can anyone tell me what I'm doing wrong? Or is it right and my expectation of a voltage in the 10s of volts wrong?

Thanks!
 
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  • #2


Hi there!

It looks like you have the right equation, but there are a few things you might want to double check. First, make sure you are using the correct units for each variable. For example, the ionisation energy of Si is typically given in eV, not just in volts. You may need to convert it to joules before plugging it into the equation. Also, the charge carrier number density should be in units of cm-3, not m-3. So you may need to convert that as well.

Additionally, make sure you are using the correct value for the permittivity of silicon (ε), which is 11.7 ε0, where ε0 is the permittivity of vacuum (8.85x10-12 F/m). This will affect your calculation of the bias voltage.

Lastly, keep in mind that the equation you are using assumes ideal conditions and does not take into account any other factors that may affect the depletion region or the voltage required to create it. So your calculated value may be an approximation and may not match the actual voltage required in a real experiment.

I hope this helps! Let me know if you have any other questions.
 

1. How do I calculate reverse bias voltage for alpha particle detection?

To calculate reverse bias voltage for alpha particle detection, you will need to know the energy of the alpha particles and the thickness of the detector material. You can then use the formula V=Ed, where V is the reverse bias voltage, E is the energy of the alpha particles, and d is the thickness of the detector material. This formula assumes a constant electric field across the detector.

2. What is the significance of reverse bias voltage in alpha particle detection?

Reverse bias voltage is important in alpha particle detection because it allows for the creation of a depletion region in the detector material. This depletion region is where the alpha particles will deposit their energy, creating electron-hole pairs that can be detected and measured.

3. Can reverse bias voltage affect the sensitivity of alpha particle detectors?

Yes, the reverse bias voltage can affect the sensitivity of alpha particle detectors. A higher reverse bias voltage can increase the size of the depletion region, making it more likely for alpha particles to interact with the detector material and be detected. However, too high of a reverse bias voltage can also lead to unwanted effects such as increased noise.

4. How can I determine the appropriate reverse bias voltage for my alpha particle detector?

The appropriate reverse bias voltage for an alpha particle detector will depend on various factors such as the type of detector material, the energy of the alpha particles, and the desired sensitivity. It is best to consult the manufacturer's guidelines or do some experimentation to determine the optimal reverse bias voltage for your specific detector.

5. Can reverse bias voltage be adjusted for different types of alpha particle detectors?

Yes, reverse bias voltage can be adjusted for different types of alpha particle detectors. The appropriate voltage will depend on the specific design and material of the detector. For example, silicon detectors typically require a higher reverse bias voltage compared to gas-filled detectors. It is important to consult the manufacturer's guidelines for the recommended reverse bias voltage for your specific type of detector.

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