In addition to drift, we can have a net movement of electrons or holes when their concentrations are not constant in various regions of a semiconductor. Let’s see what determines the rate at which this process happens.
Imagine a closed region of a semiconductor which is initially depleted from carriers and you somehow fix the concentration of electrons or hole on the left side of it. Play with the carrier velocity and average scattering time to see how diffusion rate changes.
Electron Concentration on the Left (/cm3):
Electron Velocity (cm/s):
Scattering Time (fs):
Electron/Hole
The average carrier velocity and scattering time are both functions of temperature. Instead of changing them independently, adjust the temperature and see how diffusion changes assuming that the semiconductor is lightly doped Si.
Electron Concentration on the Left (/cm3):
Temperature Range (K):
Speed (cm/s):
Scattering Time(fs):
Electron/Hole
Let’s now look at the evolution of carrier concentration and the generated current.
While you are looking at a large number of carriers, their actual number in a real semiconductor is many orders of magnitude larger. If you select to see the real world plots; therefore, they are not as noisy as the live measurements here with few carriers.
Electron Concentration on the Left: (/cm3)
Velocity (cm/s):
Scattering Time (fs):
Electron/Hole
Let’s see what happens if we have an open box and carries that reach the end of the box are taken out and never come back.
Electron Concentration on the Left (/cm3):
Velocity (cm/s):
Scattering Time (fs):
Electron/Hole
You can repeat the same experiment but this time play with temperature instead of directly changing carrier velocity and scattering time.
Electron Concentration on the Left (/cm3):
Temperature Range (K):
Speed (cm/s):
Scattering Time(fs):
Electron/Hole