Question

if phosphorous is doped with silicon and silicon is doped with boron, identify the type of semi conductions.

Answer 1

Doping means the introduction of impurities into a semiconductor crystal to the defined modification of conductivity. The conductivity of a deliberately contaminated silicon crystal can be increased by a factor of 10⁶.

1.  Elements with 5 valence electrons are used for n-doping. The 5-valent dopant has an outer electron more than the silicon atoms. Four outer electrons combine with ever one silicon atom, while the fifth electron is free to move and serves as the charge carrier. The dopants are positively charged by the loss of negative charge carriers and are built into the lattice, only the negative electrons can move. Doped semimetals whose conductivity is based on free (negative) electrons are n-type or n-doped.

2. Boron has atomic number 5. It has 3 electrons in its outer orbit, i.e. 3 valence electrons. Elements with 3 valence electrons are used for p-type doping. The 3-valent dopants can catch an additional outer electron, thus leaving a hole in the valence band of silicon atoms. Therefore the electrons in the valence band become mobile. Due to the presence of positive holes, these semiconductors are called p-conductive or p-doped. Hence when Boron is doped with Silicon, it creates p-type doping.