Semiconductors - Carrier Recombination

In summary, the initial excess electron hole pair (EHP) density of 1E14 cm^-3 does satisfy the low-level injection condition. The lifetime of the excess carriers can be calculated using the formula Tn = 1/α(no+po), but it is unclear how to find α or the intrinsic carrier concentrations with the given information. To find the excess minority carrier concentration, the time it takes for it to equal the intrinsic carrier concentration can be calculated using the previously mentioned formula. Expressions for n and p as a function of t are also needed.
  • #1
Marcin H
306
6

Homework Statement


A sample of Si at room temperature is doped with acceptors at a concentration of 3E16 cm^-3. An excess electron hole pair density of 1E14 cm^-3 is generated at some time t = 0. At t = 13.9 μs the excess EHP density is measured and found to be 5E13 cm^-3.(A). Does the initial excess EHP density satisfy the low-level injection condition? From the given information,
calculate the lifetime of the excess carriers.

(B). Given your answer to part (a), how long will it take for the excess minority carrier concentration to equal the
intrinsic carrier concentration?

(C). Give expressions of n and p as a function of t.

Homework Equations


Low Level Injection

Tn = 1/α(no+po)

The Attempt at a Solution



I am not sure how to begin this problem. How is low level injection related to EHP density? I thought we have to look at majority/minority carriers to determine that?

And for the carrier lifetime how do we find Tn without alpha, or the intrinsic carrier concentrations. I'm not sure how EHP densities can help find that.
 
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  • #2
I can find the generation rate by [(1E14 cm^-3) - (5E13 cm^-3)]/13.9us

but this isn't the equilibrium generation rate right? Or is it?
 

1. What is carrier recombination in semiconductors?

Carrier recombination is a process in which free charge carriers (electrons and holes) in a semiconductor combine and neutralize each other, resulting in a decrease in the number of charge carriers. This can occur through different mechanisms such as radiative recombination, Auger recombination, and Shockley-Read-Hall recombination.

2. How does carrier recombination affect the performance of semiconductor devices?

Carrier recombination can significantly impact the performance of semiconductor devices. For example, in light emitting diodes (LEDs), recombination of electrons and holes results in the emission of light. However, in solar cells, recombination can reduce the efficiency of converting light into electrical energy. Therefore, controlling carrier recombination is crucial in optimizing the performance of semiconductor devices.

3. What factors influence carrier recombination in semiconductors?

Several factors can affect carrier recombination in semiconductors, including material properties, impurities, defects, and temperature. For instance, the presence of impurities and defects can act as recombination centers, increasing the rate of carrier recombination. The type and concentration of dopants also play a crucial role in carrier recombination.

4. How can carrier recombination be reduced in semiconductors?

There are several strategies to reduce carrier recombination in semiconductors, such as using high-quality materials with fewer defects and impurities, optimizing the doping profile, and controlling the operating temperature. Additionally, advanced techniques such as surface passivation and quantum confinement can also help to reduce carrier recombination.

5. What are the applications of carrier recombination in semiconductors?

Carrier recombination is a fundamental process in many semiconductor-based technologies. Its applications include light emission in LEDs, photovoltaic effect in solar cells, amplification in transistors, and detection of light in photodiodes. Understanding and controlling carrier recombination is crucial for the development of efficient and reliable semiconductor devices for various applications.

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