Mobile Charge Carriers & Immobile Ions

The concept of mobile charge carriers and immobile ions is explained here by P type semiconductor material and N type semiconductor materials

Mobile Charge Carriers and Immobile Ions in P type semiconductor

• The P type semiconductor material is formed by addition of acceptor type impurity atoms ( gallium, indium, aluminum, boron ) to pure silicon / germanium crystals. 
• The number of holes added is equal to the number of boron atoms ( acceptor impurities ) because each atoms contribute one hole. 
• When hole moves away from its parent atom, the remaining atoms become negative ion. 
• This ion cannot take part in the conduction because it is fixed in the crystal structure of semiconductor. 
• The holes and electrons are movable whereas ions are not movable therefore they are called as immobile ions.

Mobile Charge Carriers and Immobile Ions in N type semiconductor

• Similarly, the N type semiconductor is formed by addition of donor type impurity atoms ( Antimony, Phosphorus, Arsenic ) to pure silicon / germanium crystals. 
• The number of free and mobile electrons are equal to the number of donor impurity atoms. 
• When electron moves away from its parent atom, it leaves behind positive ion.

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