In metallic conductors, the charge carriers are electron. because the temperature of the conductor increases, the amplitude vibrations of atoms or ions within the lattice increases, As a results of this, there are more collisions between free electrons and also the ions. Under this condition, the metal will give more opposition to the flow of electrons (i.e., current during a metallic conductor decreases). 

In case of a semiconductor, most of the electrons are within the valence band at OK (very low temperature). The thermal excitation energy is solely insufficient  and this energy isn't able to excite the electrons from the valence band to the conduction band. Thus a semiconductor behaves kind of a poor conductor (or insulator) at very coldness. However, at higher temperature even at room temperature) the electron within the valence band is thermally excited to the conduction hand.In other words, the resistance of a semiconductor decreases with increase in temperature.


What is an intrinsic semiconductor? Give examples. The semiconductor during which the current carriers (holes and electron) are created thanks to thermal excitation only across the forbidden energy gap is termed an intrinsic semiconductor.

A pure semiconductor is termed an intrinsic semiconductor. it's thermally generated current carriers.  

Explanation of the behaviour of intrinsic semiconductors on the premise of Valence-Bond theory.

What's understood by intrinsic carrier concentration?

Structure of an intrinsic semiconductor.  The lattice spacing for Germanium crystal is 5.66 Angstrom, the lattice spacing for silicon crystal is 5.43 Angstrom and also the lattice spacing for carbon crystal is 3.56Angstrom.

Each atom of silicon (Si) and germanium (Ge) has four valence electrons (i.e., electrons)  in its outermost shell). in an exceedingly very crystal of silicon or germanium, each atom forms four covalent bonds (simply noted as valence bond) by sharing its four valence electrons with the neighbouring four atoms (two-dimensional figure 10).

At OK (very low temperature), all the covalent bonds are complete Therefore, no electron is accessible within the crystal for the conduction of current. 

Generation of charge carrier (electrons & holes). At temperature. variety of the bonds are visiting be broken due to the thermal energy supplied to the crystal When a chemical bond breaks, an electron becomes free. The electron which leaves the bond is termed negatron and so the vacancy created within the bond because of the discharge of the electron is termed a hole" (i.e, deficiency of an electron). the opening is like a charge (+). This hole is filled up by an electron from the neighbouring bond, where another hole is created (figure 11). This process continues and also the opening moves within the lattice in an exceedingly random manner. 

They hit holes and recombine.  At steady-state equilibrium, the speed of the mixture of holes and electrons is solely adequate the speed of production of holes and electrons.

In an intrinsic semiconductor, the quantity density of free electrons ne(i.e. number of free electrons per unit volume) is up to the amount density of holes and is known as number density of intrinsic carriers (ni).

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