Electron versus Hole Flow:
The effect of the hole on conduction is shown in Fig. 1.7. If a valence electron acquires sufficient kinetic energy to break its covalent bond and fills the void created by a hole, then a vacancy, or hole, will be created in the covalent bond that released the electron. There is, therefore, a transfer of holes to the left and electrons to the right, as shown in Fig. 1.7. The direction to be used in this text is that of conventional flow, which is indicated by the direction of hole flow.
Fig 1.7: Electron versus hole flow
Majority and Minority Carriers:
In the intrinsic state, the number of free electrons in Ge or Si is due only to those few electrons in the valence band that have acquired sufficient energy from thermal or light sources to break the covalent bond or to the few impurities that could not be removed.The vacancies left behind in the covalent bonding structure represent our very limited supply of holes. In an n-type material, the number of holes has not changed significantly from this intrinsic level. The net result, therefore, is that the number of electrons far outweighs the number of holes.
For this reason, In an n-type material (Fig. 1.8a) the electron is called the majority carrier and the hole the minority carrier. For the p-type material the number of holes far outweighs the number of electrons, as shown in Fig. 1.8b. Therefore,
“In a p-type material the hole is the majority carrier and the electron is the minority carrier.”
When the fifth electron of a donor atom leaves the parent atom, the atom remaining acquires a net positive charge: hence the positive sign in the donor-ion representation. For similar reasons, the negative sign appears in the acceptor ion. The n- and p-type materials represent the basic building blocks of semiconductor devices. We will find in the next section that the “joining” of a single n-type material with a p-type material will result in a semiconductor element of considerable importance in electronic systems.
(a) (b)
- Light Activated SCR
- Half Wave Rectification (Part 2)
- Diode Characteristics (Part 2)
- Zener Diodes ( Part 2 )
- Zener Diodes ( Part 1 )
- Zener Diode Specification (Part 2)
- Diode Clamper
- Zener Diode Specification ( Part 1 )
- Semiconductor Diodes (Part 2)
- Atom Energy Levels
- AM Radio Transmitter
- Binary Signal
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