Photodiode carrier transit time

In summary, the conversation is about calculating the slowest possible transmit time for a carrier with 5V reverse bias applied to a GaAs photodiode. The person is having trouble with the part mentioning the "Bandgap Voltage" and is seeking hints on how to figure it out. The conversation also mentions the use of eV to measure energy gaps.
  • #1
Infidel22
5
0
Hello, I am having a bit of trouble with the following problem:

Assuming a built in voltage equal to the bandgap voltage, calculate the slowest possible transmit time for a carrier with 5V reverse bias applied to the GaAs photodiode.

I would be able to do this problem without difficulty if it wasnt for the part mentioning "Bandgap Voltage." I am familiar with bangap energy and how to calculate it, but I have no idea how to figure out the bandgap voltage for a given material. Can anyone give me any hints on this?

Thanks!
 
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  • #2
hhhmmmmm Is this something more complicated than the basic relationship between electrical energy and potential? Energy gaps are typically measured in eV because electric potential is energy per charge
 
  • #3


Hi there, I understand your confusion with the mention of "bandgap voltage." The bandgap voltage refers to the voltage at which the energy gap between the valence band and the conduction band is closed and no current can flow through the material. In other words, it is the voltage at which the material becomes an insulator. This voltage is typically equal to the bandgap energy divided by the charge of an electron (or hole). In the case of GaAs, the bandgap voltage is approximately 1.42V.

To calculate the slowest possible transit time for a carrier with 5V reverse bias applied to the GaAs photodiode, you will need to use the Shockley-Read-Hall (SRH) recombination equation. This equation takes into account the carrier lifetime, which is the average time a carrier spends in the material before recombining. The longer the lifetime, the slower the transit time.

To find the carrier lifetime, you can use the expression: τ = 1/(Nt + Ns), where Nt is the trap density and Ns is the surface recombination velocity. These values can be found in material databases or from experimental measurements.

Once you have the carrier lifetime, you can plug it into the SRH equation along with the applied voltage and the bandgap voltage to calculate the transit time. Remember to convert all units to SI units before plugging into the equation.

I hope this helps guide you in solving the problem. Good luck!
 

Related to Photodiode carrier transit time

1. What is photodiode carrier transit time?

Photodiode carrier transit time is the time it takes for an electron-hole pair to travel from the point of generation to the point of collection within a photodiode. This is an important parameter in determining the response time of a photodiode and its ability to detect changes in light intensity.

2. How is photodiode carrier transit time calculated?

The carrier transit time can be calculated using the following formula:
Tt = (W * L^2) / (2 * μ * Vbias)
Where Tt is the carrier transit time, W is the width of the depletion region, L is the length of the photodiode, μ is the carrier mobility, and Vbias is the applied bias voltage. This formula is based on the assumption that the carriers travel in a straight path from the point of generation to the point of collection.

3. What factors can affect photodiode carrier transit time?

Several factors can affect the carrier transit time of a photodiode, including the material properties of the photodiode, the size and geometry of the device, the applied bias voltage, and the temperature. In general, higher bias voltages and lower temperatures can decrease the carrier transit time, while larger device sizes and lower carrier mobilities can increase it.

4. Why is photodiode carrier transit time important?

The carrier transit time of a photodiode is an important parameter that affects the response time and sensitivity of the device. A shorter carrier transit time allows the photodiode to respond more quickly to changes in light intensity, making it suitable for applications that require fast detection, such as optical communication systems. Additionally, a shorter carrier transit time can also improve the signal-to-noise ratio of the photodiode.

5. How can photodiode carrier transit time be minimized?

To minimize the carrier transit time of a photodiode, one can use a material with a high carrier mobility, such as silicon or germanium, and optimize the device's geometry and size. Additionally, applying a higher bias voltage and cooling the photodiode can also decrease the carrier transit time. However, these measures must be balanced with other factors, such as dark current and noise, to ensure optimal performance of the photodiode.

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