Physics MCQs for NEET — Practice Questions with Answers

The NCERT states, 'At room temperature, most of the acceptor atoms get ionised leaving holes in the valence band. Thus at room temperature the density of holes in the valence band is predominantly due to impurity in the extrinsic semiconductor.'

The provided text explains, 'in extrinsic semiconductors, because of the abundance of majority current carriers, the minority carriers produced thermally have more chance of meeting majority carriers and thus getting destroyed. Hence, the dopant, by adding a large number of current carriers of one type, which become the majority carriers, indirectly helps to reduce the intrinsic concentration of minority carriers.'

The NCERT explicitly states, 'Note that the crystal maintains an overall charge neutrality as the charge of additional charge carriers is just equal and opposite to that of the ionised cores in the lattice.'

The text states, 'the donor energy level ED is slightly below the bottom EC of the conduction band and electrons from this level move into the conduction band with very small supply of energy.' This proximity means minimal energy is needed for excitation.

The NCERT text says, 'At room temperature, most of the donor atoms get ionised but very few (~10^12) atoms of Si get ionised.' This clearly indicates that donor atoms ionise predominantly.

The NCERT explains, 'Alternately, we can also say that with very small supply of energy the hole from level $E_A$ sinks down into the valence band. Electrons rise up and holes fall down when they gain external energy.'

The NCERT states this fundamental relationship: '$n_e n_h = n_i^2$ (14.5)'.

The NCERT states, 'The semiconductor’s energy band structure is affected by doping. In the case of extrinsic semiconductors, additional energy states due to donor impurities ($E_D$) and acceptor impurities ($E_A$) also exist.' This directly impacts their electrical conductivity.

The NCERT states, 'semiconductor doped with pentavalent impurity, electrons become the majority carriers... These semiconductors are, therefore, known as n -type semiconductors.' And, 'the donor energy level ED is slightly below the bottom EC of the conduction band and electrons from this level move into the conduction band with very small supply of energy.' The donor atoms 'donate' these electrons.

The NCERT says 'an electron from the valence band can jump to the level EA and ionise the acceptor negatively. (Alternately, we can also say that with very small supply of energy the hole from level EA sinks down into the valence band.) At room temperature, most of the acceptor atoms get ionised leaving holes in the valence band.' This process leaves holes in the valence band.