BJT and graph of charge density over position

In summary, to construct the charge density vs. position graph for a NPN BJT under equilibrium conditions, you would need to solve the Poisson's equation and use the Fermi-Dirac Distribution to calculate the charge density at each region. For a NPN BJT under active mode biasing conditions, the calculation becomes more complex as it also depends on the applied bias voltage. The Poisson's equation would need to be solved with the added effect of the bias voltage to determine the charge density at each region, which can then be plotted against the position on a graph.
  • #1
KasraMohammad
20
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Say you are given the problem of constructing the charge density vs position graph of a BJT(lets take a NPN BJT under equilibrium conditions for example). Now, it is a given as to how a NPN BJT Energy Band Diagram would look like through intuition or a google search. Using only the information at hand, namely the Energy Band Diagram of the NPN BJT under equilibrium, how do you go about constructing the charge density vs position graph for it?

And if the above is known how to do, how would you construct the charge density vs. position graph if one would add to the problem that the NPN BJT is actually now under active mode biasing condition?
 
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  • #2
To construct the charge density vs position graph for a NPN BJT under equilibrium conditions, you would need to first calculate the charge density at each region of the BJT. This is usually done by solving the Poisson's equation for each region and using the Fermi-Dirac Distribution to determine the charge density. Once the charge density has been calculated at each region, you can then plot it against the position (x-axis) within the BJT on a graph. If the NPN BJT is now under active mode biasing conditions, then the calculation of the charge density becomes more complicated. The charge density for each region will now not only depend on the Fermi-Dirac Distribution, but also on the applied bias voltage. To calculate the charge density in this case, one would need to solve the Poisson’s equation with the added effect of the applied bias voltage. Once the charge density has been calculated, it can then be plotted against the position on a graph as before.
 

FAQ: BJT and graph of charge density over position

What is a BJT?

A BJT, or bipolar junction transistor, is a type of semiconductor device used in electronic circuits. It is composed of three layers of differently doped semiconductor material, and has three terminals: the base, collector, and emitter.

How does a BJT work?

A BJT works by controlling the flow of current between its three terminals. When a small current is applied to the base terminal, it causes a larger current to flow between the collector and emitter terminals. This allows the BJT to amplify signals and act as a switch in electronic circuits.

What is the graph of charge density over position for a BJT?

The graph of charge density over position for a BJT is a plot of the spatial distribution of charge carriers in the device. It shows the concentration of electrons and holes in each of the three regions (base, collector, and emitter) of the BJT.

How does the charge density affect the performance of a BJT?

The charge density in the base region of a BJT is a crucial factor in determining its performance. A higher charge density in the base will result in a larger current amplification and better performance of the BJT as an amplifier or switch.

What factors can affect the charge density over position graph of a BJT?

The charge density over position graph of a BJT can be affected by various factors, such as the doping concentrations of the semiconductor materials, the width of the base region, and the applied bias voltages. Temperature and manufacturing defects can also impact the charge density distribution in a BJT.

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