Question

Which type of semiconductor is formed when silicon is doped with arsenic?

Answer 1

Hint: When we dope a group 14 element with any other element, we get an impure semiconductor. Depending upon the type of element (electron donor or electron acceptor) we doped it with n-type or p-type semiconductor. Arsenic is an electron donor species.

Complete step by step answer:
We differentiate between insulators, semiconductors and conductors on the basis of the band gap between their filled and unfilled energy levels.
We know that semiconductors are of two types namely extrinsic and intrinsic. Intrinsic semiconductors are pure semiconductors i.e. formed from a single element like pure germanium, tin etc. whereas extrinsic semiconductors are impure i.e. formed by doping of electrons.
In the question it is given to us that silicon is doped with arsenic, which means it is an impure i.e. extrinsic semiconductor. Extrinsic semiconductors are of two types. Let us discuss the types of semiconductors to find out the type of semiconductor formed when silicon is doped with arsenic.
Extrinsic semiconductors can either be p-type or n-type.
-p-type extrinsic semiconductor - When we add a group 13 element to group 14 elements, we get a p-type element. Here, it is doped with electron acceptor species, thus giving rise to 1 electron deficient species. When we dope silicon, germanium or tin with boron, aluminium, gallium, indium or thallium, we get such a semiconductor. ( Here, p stands for positive).
- n-type extrinsic semiconductor- When we add a group 15 element to a group 14 element, we get a n-type semiconductor. Here, the semiconductor is doped with an electron donor, thus giving rise to 1 electron excess species. When we dope group 14 (silicon, germanium tin) with group 14(nitrogen, phosphorus, arsenic, lead, bismuth) we get n-type semiconductor. (Here, n stands for negative).
As it is given in the question that silicon is doped with arsenic, which is a group 14 element therefore, it will be a n-type extrinsic semiconductor.
Therefore, the correct answer is doping of arsenic to silicon gives us an extrinsic semiconductor of n-type.

Note: Conductors have a very low band gap between their filled and unfilled orbitals and sometimes it’s so low that it appears as a band itself. Thus, electrons can flow to higher energy levels easily, thus they conduct electricity. Insulators have a very high band gap and thus flow of electrons is not easy thus, they are bad conductors of electricity whereas for semiconductors, the bad gap is neither too high nor too low thus they are called ‘semiconductors’.