Semiconductor

1. Semiconductor

A material whose electrical conductivity lies between that of a conductor and an insulator. Semiconductors have a small energy gap between the valence and conduction bands, allowing them to conduct electricity under certain conditions.

  • Example: Silicon (Si) and Germanium (Ge).

2. Intrinsic Semiconductor

A pure semiconductor without any significant impurity atoms. The number of free electrons in the conduction band is equal to the number of holes in the valence band.

  • Formula for conductivity: σintrinsic=e(neμe+nhμh)\sigma_{\text{intrinsic}} = e(n_e \mu_e + n_h \mu_h)σintrinsic​=e(ne​μe​+nh​μh​) Where:

    • eee = charge of an electron

    • nen_ene​ = number of electrons in conduction band

    • nhn_hnh​ = number of holes in valence band

    • μe\mu_eμe​ = mobility of electrons

    • μh\mu_hμh​ = mobility of holes

3. Extrinsic Semiconductor

A semiconductor that has been doped with impurity atoms to increase its conductivity. There are two types:

  • n-type semiconductor: Doped with pentavalent impurities (like phosphorus), resulting in more free electrons.

  • p-type semiconductor: Doped with trivalent impurities (like boron), resulting in more holes.

4. Doping

The process of adding impurity atoms to a pure semiconductor to improve its conductivity.

5. n-Type Semiconductor

A semiconductor doped with pentavalent impurity (e.g., Phosphorus), which provides extra free electrons.

  • Majority carriers: Electrons

  • Minority carriers: Holes

6. p-Type Semiconductor

A semiconductor doped with trivalent impurity (e.g., Boron), which creates more holes.

  • Majority carriers: Holes

  • Minority carriers: Electrons

7. Diode

A semiconductor device that allows current to flow in only one direction. It is made by joining a p-type and n-type semiconductor to form a p-n junction.

8. p-n Junction

The boundary between a p-type and n-type semiconductor, which forms a junction.

  • Depletion region: The region around the p-n junction where free electrons and holes have recombined, leaving behind immobile ions.

9. Forward Bias

When the positive terminal of the battery is connected to the p-type semiconductor and the negative terminal is connected to the n-type. The depletion region narrows, allowing current to flow.

10. Reverse Bias

When the positive terminal of the battery is connected to the n-type and the negative terminal to the p-type. The depletion region widens, preventing the flow of current.

11. Junction Diode as a Rectifier

A junction diode is used to convert alternating current (AC) into direct current (DC). It works in half-wave rectification and full-wave rectification.

  • Half-wave rectifier: Converts only one-half of the AC input into DC.

  • Full-wave rectifier: Converts both halves of the AC input into DC.

12. Zener Diode

A special type of diode that is designed to operate in the reverse breakdown region. It is used for voltage regulation.

  • Formula for Zener current: Iz=Vin−VzRI_z = \frac{V_{in} - V_z}{R}Iz​=RVin​−Vz​​ Where:

    • IzI_zIz​ = Zener current

    • VinV_{in}Vin​ = Input voltage

    • VzV_zVz​ = Zener breakdown voltage

    • RRR = Series resistance

13. Light Emitting Diode (LED)

A diode that emits light when current flows through it in the forward bias condition. The emitted light depends on the band gap of the semiconductor material used.

14. Photodiode

A diode that generates current when exposed to light. It works in reverse bias and is used in light-detection applications.

15. Transistor (Bipolar Junction Transistor - BJT)

A semiconductor device used to amplify or switch electronic signals. It has three regions:

  • Emitter: Heavily doped to inject charge carriers

  • Base: Thin and lightly doped

  • Collector: Moderately doped to collect charge carriers

There are two types:

  • n-p-n transistor

  • p-n-p transistor

Working of Transistor

  • In active mode: The base-emitter junction is forward biased, and the base-collector junction is reverse biased. This allows current to flow from the collector to the emitter.

Current Gain

  • Current gain in common base configuration (α\alphaα): α=IcIe\alpha = \frac{I_c}{I_e}α=Ie​Ic​​ Where:

    • IcI_cIc​ = Collector current

    • IeI_eIe​ = Emitter current

  • Current gain in common emitter configuration (β\betaβ): β=IcIb\beta = \frac{I_c}{I_b}β=Ib​Ic​​ Where:

    • IcI_cIc​ = Collector current

    • IbI_bIb​ = Base current

16. Logic Gates

Electronic circuits used in digital systems to perform logic operations like AND, OR, NOT.

  • AND Gate: Output is 1 if both inputs are 1.

    • Boolean Expression: A⋅BA \cdot BA⋅B

  • OR Gate: Output is 1 if at least one input is 1.

    • Boolean Expression: A+BA + BA+B

  • NOT Gate: Output is the inverse of the input.

    • Boolean Expression: A‾\overline{A}A

17. Integrated Circuit (IC)

A microelectronic device that integrates several electronic components like transistors, diodes, resistors, and capacitors on a small chip.