There are many examples in which the drift and diffusion currents cancel each other and keep the semiconductor at equilibrium. Such case studies are often used to prove mobility and diffusion coefficient are related (Einstein’s Relation). In this chapter, you can see a how the drift and diffusion of the carriers result in the net current to become zero when the doping profile is not constant.
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The slider below allows you to change the ratio between the doping concertation at the very right (x=100nm) to the doping concentration at the very left (x=0).
Let’s focus on majority carriers. What is the drift current when doping profile is constant (1x on the slider)? What about the diffusion current?
Change the slider to 16X and wait till the semiconductor reaches equilibrium. Watch how charge density and electric field change. Can you explain how equilibrium is reached. You can reset the scene and watch it again to better see what happens.
Use the button below that allows you to magically disable the electric field (a hypothetical scenario) and wait until steady state is reached. What can you say about diffusion current once the steady state is reached and how does the charge density compare with what you saw before when electric field was present.
Use the button above to activate the electric field and observe how the system goes back to the equilibrium.