In doping by ion implantation method 'ions' are used which are not neutral atoms. To make ions the electrons are deprived/added. In that case how-come the electron concentration in the Si changes? What is the value of the statistics based on a single electron/hole increase per atom in the doped crystal than?
I think there is some confusion. The 'electron concentration' in silicon is semconductor jargon, not real free electrons.
When implanting substances, it is easier to control the beam and impact energy when they are ionised. The impact energy can be adjusted by the voltage applied. Once this beam arrives at the surface it is neutralised. Normally a current is measured on the sample that can be used to measure the amount of deposited ions, but this current is also a consequence of the implanted ions being neutralised.
As with the 'electron concentration', this has to do with the electrons near the band gap, which confer the electronic properties of the semiconductor material. So it is semiconductor jargon, some elements being better at 'adding electrons' and others for 'adding holes'. These electron/holes are kind of virtual but behave similarly to real electrons or positive charges. What effectively happens is that a new valence or conduction band is created, and the curvature near the gamma point tells whether the virtual charges are positive or negative. So when you say 'the implantation adds electrons', it means that it adds a new band in the band structure near the fermi energy (I can't remember this is conduction or valance, I always get confused), and not real electrons, everything will neutralise.
Dear Luis Perdigao
Thanks you for your answer. Regrading this "Once this beam arrives at the surface it is neutralised.", it is understandable and makes sense. Can you refer me to some reference for it?
"These electron/holes are kind of virtual but behave similarly to real electrons or positive charges" and " So when you say 'the implantation adds electrons', it means that it adds a new band in the band structure near the fermi energy (I can't remember this is conduction or valance, I always get confused), and not real electrons, everything will neutralise. "
I am not sure if this is right. Number of electrons added by a penta-valent atom is taken exactly equal to the number of dopant atoms added per cm3 to the Si wafer. So to my understanding they are actual electrons and this is the essence of the doping process. Isn't it so?
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Atomic, Molecular and Optical Physics
- Atoms