Band bending

Okay kiddo, imagine you're playing with a see-saw with a friend. When you both sit on opposite ends of the see-saw, it balances perfectly in the middle. But what happens if your friend gets up and you stay on the see-saw? You'll go down and your end of the see-saw will touch the ground!

Now, imagine the see-saw is a layer of material and the ground is the energy level of the material. In a material, there are different energy levels that electrons can have. And just like how the see-saw tipped when your friend got off, the energy level of a material can tip when there are extra electrons or holes (where electrons could be) in one area.

When we talk about band bending, we're talking about the way the energy level of a material changes at the surface or interface with another material. This can happen because of differences in the number of electrons or holes in each material. The energy level at the surface of the first material can become higher or lower than the energy level at the surface of the second material.

Picture a hill. On one side, there are lots of people with heavy backpacks walking uphill. On the other side, there are fewer people with lighter backpacks walking downhill. When they meet at the middle, some of the people with heavy backpacks might stop and join the people with lighter backpacks and keep going downhill! The hill represents the interface, or where the two materials meet, and the backpacks represent the electrons.

So, band bending happens when the energy level of a material changes at the surface or interface because of different numbers of electrons or holes in each material. Just like how the see-saw tipped or the backpacks affected the hill, band bending can change how electrons move around and affect how well a material conducts electricity or absorbs light.