GATE ECE short notes: EDC Formula Sheet

Energy band gap for conductors is 0eV (Ideally). Energy band gap for Semiconductors is in the order of few millieV to few eV (say 1.2eV). Energy band gap for Insulators is in the order of few eV (say 5eV).

Relationship between Energy band gap and Temperature,

Ge:

Si:

N-type Semiconductor: A small amount of pentavalent impurities such as Arsenic, Antimony or Phosphorous is added to the pure semiconductor (Si or Ge).

P-type Semiconductor: A small amount of trivalent impurities such as Aluminum or Boron is added to the pure semiconductor (Si or Ge).

Conductivity of Semiconductor:

For Intrinsic Semiconductor, ==>

For N-type Semiconductor, , ==>

For P-type Semiconductor, , ==>

Fermi Function:

Concentration of Electrons in Conduction Band

Concentration of Holes in Valance Band

Fermi Level in Intrinsic Semiconductor

If Effective mass of electron and Effective mass of hole are the same ( ) then,

Fermi Level in N-type Semiconductor

Fermi Level in P-type Semiconductor

Movement of with temperature: As temperature of P-type and N-type Semiconductor increases, progressively moves towards the middle of forbidden energy gap.

At high temperatures all semiconductors behave like intrinsic semiconductors.

Mass-Action law:

Charge density in N-type Semiconductor: and

Charge density in P-type Semiconductor: and

Drift Velocity:

Drift Current Density: N-type: A/cm²        P-type: A/cm²

Diffusion Current Density:

N-type and P-type respectively :

Total Current Density:

Einstein Relation for Semiconductor:

Diffusion Length:

Diffusion Co-efficient:

PN Junction Diode:

Depletion Width (W):

Contact Potential or barrier voltage:

Diode Current Equation:

V is externally applied voltage

is 1 for Ge and 2 for Si.

Transition or Space Charge or Depletion Region Capacitance:This occurs in reverse biased condition.

Diffusion (storage) Capacitance:

Effect of Temperature on PN Junction Diode:

Note: For every 10 degree rise in temperature reverse saturation current gets doubled.

Hall Effect:

Applications:

1. To identify type of semiconductor
2. To find mobility
3. To find carrier concentration

Zener Diode: Used as voltage regulator Need Connect in Reverse Bias to operate as voltage regulator. Doping()	Varactor Diode/Varcap Always Reverse Bias Voltage Variable Capacitor Used in FM radio and TV receivers Used in very low noise micro wave parametric amplifier	Tunnel Diode: Always Forward Bias Negative resistance Fastest switch Used in microwave oscillators and reflex klystrons
LED: Always Forward Bias Spontaneous emission Direct band gap S.C used(GaAs)	PHOTO DIODE: Always Revers Biased Lightly doped i.e. large depletion width.	LASER: Light Amplification by Stimulated Emission of Radiation Population Inversion Direct Band Gap S.C used

BJT: Current Controlled Device ()

JFET: Voltage Controlled Device()

Features and Applications of JFET:

1. High input impedance and low output impedance.
2. Used as buffer in measuring instruments.

JFET as Voltage Variable Resistor:

MOSFET:

Regions of Operation: