This document discusses diodes, including: 1) Diodes are made from silicon or germanium semiconductors and function by allowing current to flow in one direction. 2) There are two types of semiconductors - N-type and P-type - which are combined to form a diode junction. 3) Diodes can be forward or reverse biased, determining whether they conduct current or act as an insulator.

1. SYMBOL OF DIODE
Cathode
(-)
Anode
(+)
DIODES W.A.D.Maduranga

2. • Silicon (Si) and Germanium (Ge) are the two most common single
elements that are used to make Diodes.
DIODE ARE MADE FROM
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
•Silicon and Germanium are both group 4
elements, meaning they have 4 valence
electrons. Their structure allows them to
grow in a shape called the diamond lattice.
•Gallium is a group 3 element while
Arsenide is a group 5 element. When put
together as a compound, Ga As creates a
zincblend lattice structure.

3. N-TYPE SEMICONDUCTOR
• N-Type: When a small amount of pentavalent impurity is added to a pure
semiconductor,it’s known as a N-type semiconductor.
Diode Is made from join P and N junctions
P-type: when a small amount of trivalent impurity is added to a pure
semiconductor,it’s called P-type semiconductor.

5. IDEAL DIODE
An ideal diode is a diode that acts like a perfect conductor when voltage
is applied forward biased and like a perfect insulator when voltage is
applied reverse biased. So when positive voltage is applied across the
anode to the cathode, the diode conducts forward current instantly.
No voltage
V-I characteristics of ideal diode
Ideal Diode Characteristics
Operation Mode On (Forward biased) Off (Reverse biased)
Current Through I>0 I=0
Voltage Across V=0 V<0
Diode looks like Short circuit Open circuit

6. FORWARD BIAS
When voltage is applied across a diode in such a way that the diode allows current
and the potential barrier reduced, the diode is said to be forward-biased.
REVERSE BIAS
When voltage is applied across a diode in such a way that the diode prohibits
current and potential barrier increase, the diode is said to be reverse-biased.

7. Under reverse bias, the depletion region
becomes wider.after fully stops the current
through the diode
Under Forward bias, the depletion region
reduce.after go current through the diode.

8. V-I characteristics of diode

9. Silicon vs Germanium I-V
si
ge

10. TYPES OF DIODES
ZENER DIODE
A Zener Diode allows current to flow from its anode to its cathode like a
normal semiconductor diode, but it also permits current to flow in the reverse
direction when its "Zener voltage" is reached. Zener diodes have a highly doped p-n
junction. Normal diodes will also break down with a reverse voltage but the voltage
and sharpness of the knee are not as well defined as for a Zener diode. Also normal
diodes are not designed to operate in the breakdown region, but Zener diodes can
reliably operate in this region.

11. A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n
junction diode, which emits light when activated.[4]When a suitable voltage is
applied to the leads, electrons are able to recombine with electron holes within the
device, releasing energy in the form of photons. This effect is
called electroluminescence, and the color of the light (corresponding to the energy
of the photon) is determined by the energy band gap of the semiconducto
LIGHT EMITTING DIODE(LED)

12. PHOTO DIODE
While LEDs emit light, Photodiodes are sensitive to received light. They are
constructed so their pn junction can be exposed to the outside through a clear
window or lens.
symbol

13. RECTIFIER CIRCUITS
In half-wave rectification of a single-phase supply, either the positive or negative
half of the AC wave is passed, while the other half is blocked. Because only one
half of the input waveform reaches the output, mean voltage is lower. Half-wave
rectification requires a single diode in a single-phase supply, or three in a three-
phase supply. Rectifiers yield a unidirectional but pulsating direct current; half-
wave rectifiers produce far more ripple than full-wave rectifiers, and much more
filtering is needed to eliminate harmonics of the AC frequency from the output.
HALF WAVE RECTIFIER CIRCUITS
APPLICATION OF DIODE
input output

14. FULL WAVE RECTIFIER CIRCUITS
A full-wave rectifier converts the whole of the input waveform to one of constant
polarity (positive or negative) at its output. Full-wave rectification converts both
polarities of the input waveform to pulsating DC (direct current), and yields a higher
average output voltage. Two diodes and a center tapped transformer, or four diodes in
a bridge configurationand any AC source (including a transformer without center tap),
are needed.[3] Single semiconductor diodes, double diodes with common cathode or
common anode, and four-diode bridges, are manufactured as single components.
input
output

15. SOURCES
https://en.wikipedia.org/wiki/Diode
www.google.com
http://www.electrical4u.com/diode-working-
principle-and-types-of-diode/
https://learn.sparkfun.com/tutorials/diodes

16. THANK YOU