I have just started to read some basic concepts of semiconductor electronics.I am facing problems regarding the following points,so it would be great if you could please address the following
1.Why is the valence band completely filled at 0 K and conduction band completely empty at the same temperature.?
I know it has something to do with the third law of thermodynamics that a system has minimum randomness at 0 K but if electrons are in a single band,it increases randomness.Doesnot it?please give me some intuition and correct me if i am wrong somewhere.
2.Is it always true that the number of energy states in the valence band is the same as the number of energy states in the conduction bandin the solid state of a semiconductor. number of energy states is equal to the sum of maximum permissible electrons in the outer shell of the atom
For example,silicon has 4 electrons(3s2,3p2) in its outermost shell.for n atoms of silicon in a solid is it necessarily be true that there will be 8n states which are equally divided among conduction and valence bands.The 4n states of valence band is completely filled whereas 4n states of conduction band are empty.this is the case when no excitation is given to the solid semiconductor.
I basically could not see what is the intuition behind these facts.My teacher says that it is a theory and i have to mug it up.but i am not satisfied.any intuition or reasoning shall be of much help.
3.Why the depletion layer width decreases when a p-n junction diode is under forward bias?
I know that in forward bias,the applied voltage is opposite to the built in voltage due to accumulation of charges in the depletion layer.also in such case,the diffusion curent increases many times but the drift current becomes negligible.
4.how does a centre tap transformer rectifier function?
I could not quite get to understand what is the role of centre tap in this case and how does it help to generate full wave fluctuating dc current.
please don't hesitate to respond if you donot have the correct idea to any one or two of the questions.Thanks in advance.