Semiconductor Devices and Optoelectronics

1
Semiconductor Devices and Optoelectronics
EBB 424/3
2
Semiconductor Devices and Optoelectronics

• Part 1 (7 weeks)
• Semicond Devices
• (A/P. Dr. Cheong)

• Part 2 (7 weeks)
• Optoelectronics
• (A/P. Dr. Sabar)

3
Course Outcomes

• Part-1
• Able to analyze and compare a bipolar junction
  transistor and field effect transistor using I-V
  and C-V characteristics.
• Able to design and analyze a metal oxide
  semiconductor field effect transistor devices.
• Able to describe the principle of operation and
  fabrication of nanoelectronic devices such as
  single-electron transistors.

• Part-2
• Able to describe the principle of operation and
  materials selection for common optoelectronic
  devices (LED, LASER, photodiode, photodetector
  and photovoltaic.
• Able to design and develope a simple photovoltaic
  (solar cell) devices.

4
Part -2Optoelectronics

• Assoc. Prof. Dr. Sabar D. Hutagalung
• mrsabar_at_eng.usm.my
• www.sdhutagalung.com
• Ext. 6171, Room SR 2.11

5
Topics - Overview

• Introduction to Optoelectronics 1 hr
• Light-semiconductor interaction 3h
• Light Emitting Diodes (LEDs) 4 hrs
• LASER 5 hrs
• Photodetectors and Photodiodes 3 hrs
• Photovoltaics (Solar cells) - 6 hrs

6
References

• Joachim Piprek, Semiconductor Optoelectronic
  Devices, Academic Press, 2003.
• S. O. Kasap, Optoelectronics and Photonics
  Principles and Practices, Prentice-Hall, 2001.
• J. Nelson, The Physics of Solar Cells, World
  Scientific Pub., Singapore, 2004.

7
Schedule - tentatively

• 24/10 (Mon) 1h Introduction to Optoelectronics
• 31/10 (Mon) 1h Lights
• 01/11 (Tue) - 2h Lights
• 14/11 (Mon) 1h LEDs
• 15/11 (Tue) 2h LEDs
• 21/11 (Mon) 1h LEDs
• 22/11 (Tue) 2h Laser
• 28/11 (Mon) 1h Laser
• 29/11 (Tue) 2h Laser
• 05/12 (Mon) 1h Photodiodes/Photodetector
  Submit assignment
• 06/12 (Tue) 2h Photodiodes/Photodetector
• 12/12 (Mon) 1 h Solar Cells
• 13/12 (Tue) 2h Solar Cells TEST (8-9 pm?)
• 19/12 (Mon) 1h Solar Cells
• 20/12 (Tue) 2h Solar Cells

8
Marking Scheme

• Course work 40 Final Exam 60 (Total 100)
• CW from Part-2
• Assignment (1) 10 (Poster presentation)?
• Test (1) 8
• Quiz (1) 2
• Total 20
• Important date
• Assignment questions release 21 Nov 2011
• Assignment submission date 05 Dec 2011
• Test (part-2) Mon, 13 Dec 2011 (8-9 pm)

9
(No Transcript)
10
WARNING!!!

• It is expected that you will regularly attend
  class and be on time for class.
• Late arrivals to class are distracting the class
  activity (door might be locked after 5 min).
• Attendance for this class is not part of the
  course grade, but please take note that absent
  gt2X no final exam.
• No mobilephone activities call,sms, etc.

11
Introduction to Optoelectronic Devices
12
Optoelectronics

• Optoelectronics is the study and application of
  electronic devices that source, detect and
  control light, usually considered a sub-field of
  photonics.
• Optoelectronic devices are electrical-to-optical
  or optical-to-electrical transducers, or
  instruments that use such devices in their
  operation.
• Electro-optics is often erroneously used as a
  synonym, but is in fact a wider branch of physics
  that deals with all interactions between light
  and electric fields, whether or not they form
  part of an electronic device.

13
What is Light?

• Light or visible light is electromagnetic
  radiation that is visible to the human eye, and
  is responsible for the sense of sight.
• Visible light has wavelength in a range from
  about 380 to about 740 nm, with a frequency range
  of about 405 THz to 790 THz.

Electromagnetic wave
14
EM Spectrum
15
Lights Newton vs Huygens

• Lights as wave?
• Lights as particles?

Huygens
They did not agree with each other!
Newton
16
Light interaction with solids

• Optical classification
• Transparent
• Transluscent
• Opaque

17
Semiconductor

• A semiconductor is a solid material that has
  electrical conductivity in between a conductor
  and that of an insulator.
• Silicon (Si) is the most semiconductor material,
  but dozens of other materials are used as well.

18
(No Transcript)
19
Why semiconductor materials are so useful?
20
Why semiconductor materials are so useful?

• The main reason is that the behaviour of a
  semiconductor can be easily manipulated by the
  addition of impurities, known as doping.

21
Why semiconductor materials are so useful?

• Semiconductor conductivity can be controlled by
  introduction of an electric field, by exposure to
  light, and even pressure and heat
• thus, they can make excellent sensors.
• Current conduction in a semiconductor occurs via
  mobile or "free" electrons and holes,
  collectively known as charge carriers.

22
Diode

• Diode is a simplest semiconductor devices.
• A diode has a low resistance in one direction and
  a high resistance to it in the reverse direction.
  
• This property makes a diode useful as a
  rectifier, which can convert AC into DC.

23
Real diode (p-n junction)
A typical p-n junction diode characteristic curve
24
What is LED?
LEDs are semiconductor p-n junctions that under
forward bias conditions can emit radiation by
electroluminescence in the UV, visible or IR
spectrum regions. The quanta of light energy
released is approximately proportional to the
band gap of the semiconductor.
25
The pn Junction LED

• Electron-hole recombination is the process that
  occurs in diodes.
• In a regular diode recombinations release energy
  thermal (heat) nonradiative recombination.
• In an LED recombinations release the light
  radiative recombination.
• In reality, both types of recombination occur in
  a diode, when a majority of recombinations are
  radiative, we have an LED.

26
LEDs
LEDs
Red LED
White LED
LED for displays
Blue LED
LED for traffic light
27
Photodiodes

• The photodiode is a p-n junction under reverse
  bias.
• Exposing a semiconductor to light can generate
  electron-hole pairs, which increases the number
  of free carriers and its conductivity.
• Only those that have correct wavelength can be
  absorbed by the semiconductor.
• Separation of charge can be collected and
  measured as current or voltage.
• If device is left open circuit ? voltage detected
  ? photovoltaic effect
• If device is short-circuited (or under reverse
  bias) ? photoconductive mode

28
Photodetectors

• When a photon/light strikes a semiconductor, it
  can promote an electron from the valence band to
  the conduction band creating an electron-hole
  (e-h) pair.
• The concentration of these e-h pairs is dependent
  on the amount of light striking the
  semiconductor, making the semiconductor suitable
  as an optical detector.
• There are two ways to monitor the concentration
  of e-h pairs
• In photodiodes, a voltage bias is present and the
  concentration of light-induced e-h pairs
  determines the current through semiconductor.
• Photovoltaic detectors contain a p-n junction,
  that causes the e-h pairs to separate to produce
  a voltage that can be measured.

29
Solar Cell/Photovoltaic Device

• Photovoltaic devices or solar cells are
  semiconductor p-n junction that can convert solar
  radiation into electrical energy.

Diagram of a PV cell.
Photovoltaic cells, modules, panels and arrays.
Major photovoltaic system components.
30
Converting Sunlight to Electricity

• A typical PV cell consists of semiconductor p-n
  junction.
• Sunlight striking the cell raises the energy
  level of electrons and frees them from their
  atomic shells.
• The electric field at the p-n junction drives the
  electrons into the n region while positive
  charges are driven to the p region.
• A metal grid on the surface of the cell collects
  the electrons while a metal back-plate collects
  the positive charges.

31
Converting Sunlight to Electricity
32
Solar Cells
33
Laser

• For atomic systems in thermal equilibrium,
  emission of light is the result of two main
  processes
• ABSORPTION of energy
• SPONTANEOUS EMISSION of energy (a random photon
  is emitted)
• A third mechanism is crucial to the formation of
  LASER action, which is
• STIMULATED EMISSION.
• Light Amplification of Stimulated Emission
  Radiation

34
Laser
Basic optical transitions
35
Diode Laser
Diode lasers have been used for cutting, surgery,
communication (optical fibre), CD writing and
reading etc
36
The power-current curve of a laser diode. Below
threshold, the diode is an LED. Above threshold,
the population is inverted and the light output
increases rapidly
37
Boltzmann distribution vs Population inversion
How to create a population inversion?
38
Laser
39
(No Transcript)