# Why is silicon a good dopant for GaAs?

I have been looking into how GaAs and InGaAs quantum dots can be doped to make them negatively charged and I've found that they are doped will silicon. However, I'm struggling to understand why silicon is a good dopant, as it has 4 electrons in its outer shell. Does anyone have an explanation for this?

• do you mean n-doped instead of negatively charged? – A.K. Apr 1 '19 at 17:19
• Yes I mean n-doped, but when the material is n-doped to the correct level there will be a single excess electron contained in the quantum dot. – JJH Apr 1 '19 at 17:21

It's a good n-dopant because silicon has 4 valence electrons and gallium/indium have 3. When a silicon atom occupies a gallium site (Kröger-Vink Notation: $$\mathrm{Si^\bullet _{Ga^{3+}}}$$) in the crystal the silicon has the extra valence electron compared to a $$\mathrm{Ga^{3+}}$$ ion thus making the material n-doped.