Before we begin our journey looking at how semiconductor devices work, we need to understand the inner workings of atoms. The Hydrogen Atom, due to its simple structure, provides a good starting point to understand the fundamentals, before we move onto semiconductors such as Silicon.

The Subatomic Particles

A hydrogen atom has one electron, one proton, and no neutrons .

What is the net charge of the hydrogen atom?

What is the total weight of the hydrogen atom?

The Classical Model

The Classical Model is a planetary model.

Why is the proton stationary and only the electron orbits?

This simple model based on classical physics cannot explain many of the atom’s properties.

The Quantum Model

At such a small scale, we can never predict the exact location of a particle. At any point in time, in principle we can obtain the electron position only if we perform a “measurement.” If we repeat the measurements many times, we can obtain the probability of finding the electron at various positions.

Perform the measurement many times and see if you find a pattern. Where is most likely to find the electron?

Exploring the Distribution

If you do thousands of experiments and keep a trace of each measurement you would see something like this. Now, where do you think it is most likely to find the electron?

Probability vs. Distance

You might have guessed the likelihood of finding the electron increases the closer you get to the nucleus. To test this impression, let’s count the number of times electron is found between these two spherical shapes.

Where do you count the most? The closer to the nucleus , the farther, or somewhere in the middle?

Zooming Out

As we zoom out and increase the number of experiments, we can see that a few times the electron may be located far from the nucleus. However, the probability drops rapidly.

The 2s Orbital

What you saw was the electron in its lowest energy level which is the most stable condition. If we excite the electron by, for example, shining light on it, the electron can go to the next energy level which is the 2s Orbital.

Where is most likely to find the electron when it is the 2s orbital.

The 2px Orbital

There are three other orbitals with the same energy as 2S: 2px, 2py and 2pz. Here is the pattern you see for 2px orbital. Where do you think it is unlikely to find the electron?

At what distance from the nucleus is it most likely to find the electron?

2py and 2pz

These orbitals are identical to the 2px orbitals except for their orientation. Here is the pattern you see for 2px orbital. Where do you think it is unlikely to find the electron?

For the sake of simplicity

We now understand that an electron's position is not fixed, and it can exist anywhere. However, such a definition would not allow us to study its interaction with other charge carriers, which is necessary to solidify the concepts of semiconductor physics

Hence, for the sake of simplicity, in the following lessons, we will visualize the electron as being static. However, the visualization of the orbital of the electron should remind you, that it is not in fact so!