The document discusses photodiodes and LEDs. Photodiodes are a type of photo detector that can convert light into current or voltage. They have a PN or PIN junction and operate by generating a photocurrent when photons are absorbed in the depletion region. Photodiodes are used in applications like light sensors, smoke detectors, and for measuring light intensity. LEDs are semiconductors that emit light through electroluminescence when forward biased. They have advantages over incandescent bulbs like longer lifetime and higher efficiency. LEDs find applications in devices like phones and cameras.

1. Photodiode
Sahil Bansal
Sahil Chhabra

2. •A photodiode is a type of photo detector
capable of converting light into either current
or voltage
•It converts light energy into electrical energy.
•Photodiodes are similar to regular
semiconductor diodes except that they may
be either exposed with a window or optical
fibre to allow light to reach sensitive part of
device

3. Material commonly used for
producing photodiode
includes:

4. Working of Photodiode
 Photodiodes are of two types PN and PIN.
 At PN junction there will be concentration
gradient that causes electrons to diffuse
into p-type region and holes into n-type
region. This diffusion results in an opposing
electric potential, often referred to as an
Depletion region.
 Any photon absorbed in the depletion
region causes moment of charge carriers

5.  This moment of charge carriers across the junction
upsets the electrical balance and produces a
photocurrent, which can be detected at
electrodes.

7. Applications
In electronic devices
In smoke detectors
• Light sensors
• Used to measurer light intensity in
science and industry

8. What is LED?
LED are semiconductor p-n junctions that under forward bias conditions can emit
radiation by electroluminescence in the UV, visible or infrared regions of the
electromagnetic spectrum. The qaunta of light energy released is approximately
proportional to the band gap of the semiconductor.

9. Applications of LEDs

10. Your fancy telephone, i-pod, palm pilot
and digital camera

11. Getting to know LED
Advantages of Light Emitting Diodes (LEDs)
Longevity:
The light emitting element in a diode is a small
conductor chip rather than a filament which greatly
extends the diode’s life in comparison to an
incandescent bulb (10 000 hours life time compared
to ~1000 hours for incandescence light bulb)
Efficiency:
Diodes emit almost no heat and run at very low
ampere.

12. How does it work?
P-n junction Electrical
Contacts
A typical LED needs a p-n junction
There are a lot of electrons and holes at
the junction due to excitations
Electrons from n need to be injected to p
to promote recombination
Junction is biased to produce even more
e-h and to inject electrons from n to p for
recombination to happen
Recombination
produces light!!

13. Thank you