SPM Physics: Semiconductor

Basically,this topic wont be too difficult if u took chemistry in SPM.
As usual, u need to understand the meaning of semi conductor..

Lets start with the word 'semi' &  'conductor'..do u really understand what is conductor???Do u have any idea the word 'semi' is?? If u dont, i m not gonna give u the answer..take out a dictionary & start searching on your own..dont be lazy to THINK!!

So what is semiconductor??
Hmm again..Should i give u the answer??.. may b not!. coz its all in the text book or any reference book! I'm sure your parents have spent some money to buy a reference book for u..so why dont u learnt to USE IT!! I can bet most of your reference book, or exercise book are still looked neat & tidy as if u just bought it yesterday. So i think its time to do some 'conteng-conteng' on those books.Learning physics will be easier if u are not the type who is too lazy to think and  to reason logically ..but if u are the lazy type,frankly speaking its hard for u to get even a 'B'.
I might sound a bit harsh ..However dont take it too personal, bukan apa just to wake u up from your 'ignorance' attitude... at the same time i m trying my best to guide u to learn physics effectively.

Alright, lets get back to this topic..
How to describe semiconductors in terms of resistance & free electrons???
Usually pure semiconductors or intrinsic semiconductors are made from silicon or germanium. It conducts electricity when it has more free electrons especially under high temperature. However at low temperature, semiconductor produce few free electrons which makes it hard to conduct electricty. Thus the semiconductor acts as an insulator, i.e it has higher resistance.



So in simple words , semiconductor is actually a substance with its resistivity is between a conductor and an insulator. However u must bear in mind that its conductivity is not as good as conductor. So the question is,how are we going to make it a better conductor??

The answer is by having a DOPING process....hmm..What is DOPING????
It is a process to increase the conductivity of a pure semiconductor by adding an impurities.
In the end extrinsic semicondutors are produced.

There are two type of doping:

1. P-type

• p type is made by adding trivalent atom such as Boron
• trivalent atom has 3 electron in outer shell, one less than silicon.
• an extra hole is provided and this holes act as majority charge carrier for p-type

2. then we have a n- type :

•  it is made by adding pentavalent atom such as phosphorus
• pentavalent atom has 5 electrons in outer shell & 4 of them used to make covalent bond with silicon
• an extra unused electron  act as free electron which is the majority charge carriers for n type.