Problem Understanding Physics/Electronics: Trivalent vs. Pentavalent Impurities

[paulmdrdo1]

I'm having a problem understanding what I've read from an electronics book.

can you explain why the trivalent impurities
exert lower forces on the outer-shell electrons than the pentavalent impurities?
and why The valence and conduction bands in an n-type material are at slightly lower energy levels
than the valence and conduction bands in a p-type material?

a lot of thanks!

 

[Aaron Bex]

Trivalent impurities exert lower forces on the outer-shell electrons than pentavalent impurities because trivalent impurities have three valence electrons instead of five. When these impurities become part of a crystal lattice, their three valence electrons are shared with other atoms in the lattice, thus creating weaker bonds and weaker forces on the outer-shell electrons.

The valence and conduction bands in an n-type material are at slightly lower energy levels than the valence and conduction bands in a p-type material because n-type materials contain more free electrons. These free electrons reduce the energy of the valence and conduction bands due to electrostatic attraction. P-type materials, on the other hand, contain fewer free electrons, so their valence and conduction bands are at higher energy levels.