DIODE

1. The Diode
Lecture 2
By : ENGR. SALMAN HAMEED

2. Last Lecture
 Atomic Structure
 Classification of matter on the basis of
semiconductor theory
 Covalent Bond
 Conduction in semiconductors
 N-type and P-type Semiconductors

3. Lecture Overview
 The Diode
pn junction
Formation of Depletion Region
Energy Diagrams of the pn junction and Depletion Region
 Biasing a Diode
Forward Bias
Reverse Bias

4. Diodes
 N region has lots of free electrons
 P region has lots of holes
 At equilibrium: total number positive and negative
charges is the same (@ room temp)
 At the pn junction the electrons and holes with
different charges form an electric field
 In order to move electrons through the electric field
(generate current) we need some force (voltage)
– This potential difference is called barrier voltage
– When enough voltage is applied such that electrons
are moved then we are biasing the diode
– Two layers of positive and negative charges for
depletion region – the region near the pn-junction is
depleted of charge carriers)

5. Energy Diagrams
(pn junction and Depletion Region)
At instant of junction
Formation
At equilibrium

6. Biasing Types of a Diode
 Forward bias
– Bias voltage VBias > barrier voltage
VBar
– Reduction in + and – ions  smaller
depletion region
– VBar Depends on material, doping,
temp, etc. (e.g., for silicon it is 0.7 V)
 Reverse bias
– Essentially a condition that prevents
electrons to pass through the diode
– Very small reverse break down current
– Larger depletion region is generated
Cathode
n region
Anode
p region
Connected to the
negative side of
the battery
Connected to the
positive side of
the battery
A K

7. Biasing Types of a Diode (Forward)
Cathode
n region
Anode
p region
A K
Moving
electrons
Small dynamic resistance
VBias
n
p
Conventional
Current Flow
Conventional
Current Flow
I (Forward)

8. Very Small
Moving
Electrons:
Reverse Current)
Biasing Types of a Diode (Reverse)
Cathode
n region
Anode
p region
A K
Large resistance
VBias
n
p
Conventional
Current Flow
Holes are left
behind; large
depletion region
Instant pull of
electrons

9. Reference
- Chapter 01 (Section 1.7 and 1.8)
“Electronic Devices” by Floyd, Seventh Edition