ETE411 :: Lec12

Dr. Mashiur Rahman

What we will learn today?

• The pn Junction Diode.

– Zero bias, reverse bias, forward bias

– Calculate the minority carrier diffusion current density at the edge of the space charge region.

– Current voltage characteristics with a forward-bias voltage.

Terms and Notations

Zero bias

Energy band diagram

Reverse bias

Forward bias

comparison

Zero bias reverse bias forward bias

Reverse bias

Energy band diagram

Space charge width

W= xn+xp

Example 7.3 (page 249)

Solution

Forward bias

Conduction band energy through a pn junction (forward bias)

Boundary Condition

Calculate the minority carrier diffusion current density at the edge of the space charge region.

kT

eVnn a

pp exp0

kT

eVpp a

nn exp0

Minority carrier electron concentration in the p region

Minority carrier hole concentration in the n region

Reference : page 271 - 274

Example 8.1

Solution

Idea pn junction current

Steady-state minority carrier concentration

Space charge region

Electron and hole current densities through the space charge region of a pn juction

Reference : page 278 - 279

I-V characteristic of a pn junction diode

Idea electron and hole current components through a pn junction under forward bias