INTRINSIC SEMICONDUCTOR
(1) An intrinsic semiconductor, also called an Undoped semiconductor or pure semiconductor
(2) In an intrinsic semiconductor the number of electrons in the conduction band is equal to the number of holes in the valence band means n=p
(3) An intrinsic semiconductor material is chemically very pure and possesses poor conductivity.
(4) An intrinsic semiconductor behaves like an insulator at OK that means valence electron in semiconductor are tightly bounded with atom and these are not free to wander in crystal
(5) The energy required to break a Covalent bond at OK for Si crystal is 1.21eV and for Ge this is .785eV
(6) Si intrinsic semiconductors have crystal structure shown in figure at 0K
(7) Ge intrinsic semiconductors have crystal structure shown in figure at 0K
(8) The crystal structure of germanium and silicon have regular repetition of atoms and one particular atom made Covalent bond with its four neighbor atoms and this pattern repeat throughout the crystal
(9) An atom of Si crystal structure have four valence electron , these all electron are tightly bounded by the nucleus and at OK they are not available for the conduction
(10) At room temperature due to thermal agitation some of Covalent bond will be broken means some of electrons gain enough energy to get unbounded with atom and free to move throughout in the crystal and a holes generates
(11) At room temperature Si intrinsic semiconductors crystal structure shown in figure
(12) The energy required to break a Covalent bond at room temperature (25C) for Si crystal is 1.1eV and for Ge crystal .72eV
(13) the number of thermally excited electrons cm–3 in silicon (Si) at 298 K is 1.5 × 1010. In gallium arsenide (GaAs) the population is only 1.1 × 106 electrons cm–3. This may be compared with the number density of free electrons in a typical metal, which is of the order of 1028 electrons cm–3.
(14) At room temperature The absence of the electron in the covalent bond is represented by the small circle and such an incomplete covalent bond is called a “Hole”
(15) The mechanism by which a Hole contribute to the conductivity is qualitatively as follow:
When a bond is incomplete so that a hole exists, it is relatively easy for a valence electron is a neighboring atom to leave its covalent bond to fill this hole , an electron moving from a bond to fill a hole leave a hole in its initial position , hence the hole moves effectively in direction opposite to that of electrons
(16) Best examples of intrinsic semiconductors are Si and Ge
