Estimate the number of electrons flowing in a semiconductor pn junction

In summary, the conversation discusses the drift current in a p-n junction and how to estimate the number of electrons crossing a cross section per second in the depletion region. The solution involves calculating the current due to electrons and holes separately and then adding them together to get the total junction current. If the doping levels are equal, one or more parameters will account for the ratio of hole current to electron current.
  • #1
nishantve1
76
1

Homework Statement



The drift current in a p-n junction is 20μA . Estimate the number of electrons crossing a cross section per second in the depletion region.

Homework Equations



Drift current is the current that occurs due to formation of holes and electrons in the depleted region from where the electrons and the holes are sucked away to the respective sides . This creates a current from n to p . Called the drift current The drift current is a result of flow of both holes and electrons.

The Attempt at a Solution



So the electrons and the holes both equally contribute to the drift current . So the current due to the electrons would be 10μA . So that means
10 * 10^(-6) C flowing per second
charge on one electron = 1.6 * 10^-19 C

so we can write

n * 1.6 * 10^-19 C =10 * 10^(-6)
n = 6.25 * 10^13 electrons .


But the answer given is 3.125 * 10 ^ 13 , half of what I calculated .
Where am I wrong ?
 
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  • #2
I post this mainly since no one else has; it's not my specialty:

You can't assume that half the charges are electrons & the other half holes.

Each carrier current must be computed separately based on the respective charges' diffusion constants, minority carrier concentrations, and diffusion lengths (lifetimes); all figure separately for electrons and holes. Finally, you add the two to get the total junction current.

If the problem assumes equal n and p doping levels then one or more of the above parameters is such that the respective parameter ratio for holes & electrons accounts for the 3:1 ratio of hole current vs. electron current.
 

FAQ: Estimate the number of electrons flowing in a semiconductor pn junction

1. How does a semiconductor pn junction work?

A semiconductor pn junction is a junction between two regions of a semiconductor material, one doped with a higher concentration of positive charge carriers (p-type) and the other doped with a higher concentration of negative charge carriers (n-type). When these two regions are connected, an electric field is created at the junction, which causes electrons to flow from the n-type region to the p-type region, and holes (positive charge carriers) to flow in the opposite direction. This flow of charge creates a current, allowing the pn junction to function as a diode or other electronic device.

2. How do you estimate the number of electrons flowing in a semiconductor pn junction?

The number of electrons flowing in a semiconductor pn junction can be estimated using the equation I = A * q * n * v, where I is the current, A is the junction area, q is the elementary charge, n is the electron concentration, and v is the electron velocity. The electron concentration can be measured using methods such as Hall effect measurements, and the electron velocity can be calculated based on the material properties of the semiconductor.

3. What factors affect the number of electrons flowing in a semiconductor pn junction?

The number of electrons flowing in a semiconductor pn junction is affected by several factors, including the material properties of the semiconductor (such as doping concentration and bandgap), the temperature, the applied voltage, and the physical dimensions of the junction.

4. How does the number of electrons flowing in a semiconductor pn junction change with temperature?

As the temperature increases, the number of electrons flowing in a semiconductor pn junction also increases. This is because at higher temperatures, more electrons in the valence band gain enough energy to jump to the conduction band, increasing the electron concentration and therefore increasing the current flowing through the junction.

5. Can the number of electrons flowing in a semiconductor pn junction be controlled?

Yes, the number of electrons flowing in a semiconductor pn junction can be controlled by adjusting the doping concentration, the applied voltage, and the physical dimensions of the junction. By carefully designing and controlling these factors, electronic devices with specific current flow characteristics can be created using pn junctions.

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