Question: The secrets of semiconductors? And what is your favourite one to use? Why? :)

Suze Kundu answered on 21 Jun 2011:

Hi Caitlhan!

So, semiconductors are basically in between an insulator and a conductor. In an insulator, like rubber, it takes loads of energy to make it do anything exciting, because there is a big energy gap that needs to be overcome for the electrons to want to move to a level where they can move around. In a conductor like copper wire, the energy level is small, or barely there at all, so it doesn’t take much energy at all forthe electrons to move around.

A semiconductor is in between. The energy needed to excite the electrons from their lazy state to their excitable state is bigger than in a conductor, but not as huge as an insulator. This makes it a really good type of material to use as a photocatalyst, which is a material that can speed up a light dependent reaction.

My favourite semiconductor is titanium dioxide, because it is really strong, and useful for my work. It makes some really beautiful pink-ish thin films. It has a band gap (the name given to the energy that you need to excite the electrons) of 3.2 eV (electron volts).

Light waves have energy. You know when you pass light through a prism, or sunshine goes through raindrops, you get a rainbow effect? The rainbow happens because all the colours are separated out. Each colour has its own energy. The blue end have more energy, and the red end have less energy. Their wavelengths vary too, depending on this energy. The blue end has a smaller wavelength, and the red has a bigger wavelength, so the peaks and dips are closer together in the blue area than in the red, where they are more spread out.

To overcome the band gao of 3.2 eV for titanium dioxide, you would need energy from light that has a wavelength of 380 nm (nanometers, which is tiny) or less (less because it is then more energetic light) to excite the electron up in to the energy level where it wants to move around. When sunlight hits the titanium dioxide, that little bit of blue light in the ultra violet region of sunlight excites an electron in the titanium dioxide. The electron can then go on to attack a water molecule and reduce it to hydrogen, which we can collect as a gas. This is how I’m splitting water using sunlight!

Did that make sense? Let me know if you have any more questions about it!