1. EBB 424E Semiconductor Devices and Optoelectronics
SMMRE,USM
EBB 424E Semiconductor Devices and Optoelectronics
Part II - Optoelectronics
Dr Zainovia Lockman

2. EBB 424: Semiconductor Devices and Optoelectronics
Part 1:
Semiconductor Devices
Dr. Sabar D. Hutagalung
Part 2:
Optoelectronics
Devices
Dr Zainovia Lockman
70% Exam 30% Coursework

3. Contents of the Course Optoelectronics Light sources Light Detectors
LED
Photodetector
LASERS
Photoconductor
Photovoltaic

4. Scope of the Course
By the end of the course you will be able to describe various optoelectronics devices.
In particular you need to be able to describe:
The device configuration
Materials requirements
Materials selection
Materials issues

5. What is Optoelectronics?
"Optoelectronics, the alliance of optics and electronics, [is] one of the most exciting and dynamic industries of the information age. As a strategic enabling technology, the applications of optoelectronics extend throughout our everyday lives, including the fields of computing, communication, entertainment, education, electronic commerce, health care and transportation. Defense applications include military command and control functions, imaging, radar, aviation sensors, and optically guided weapons. Optoelectronics businesses manufacture components such as lasers, optical discs, image sensors, or optical fibers, and all sorts of equipment and systems that are critically dependent on optoelectronics components. Optoelectronics technology is a key enabler of the USD$1.5 Trillion global information industry."

6. Light- Emitting Diodes
LEDs
Red LED
White LED
LED for displays
Blue LED
LED for traffic light

7. DIODE LASERS
Diode lasers have been used for cutting, surgery, communication (optical fibre), CD writing and reading etc

8. Producing Laser in the Lab

9. Optoelectronic devices for Photovoltaic Applications

10. Solar Cells

11. Fibre optics Communication Transmitter  Channel  Receiver
IR - Lasers
Fibre Optics
IR- Photodetector
Transmitter
Channel
Receiver

12. Head Mounted Display  Applications: Next generation head mounted display and virtual reality training

13. What is expected of you?

14. Objectives of the Part II EBB424E
To describe the fundamentals of photon-electron interaction in solid and to relate such understanding with the optoelectronics devices
To develop an appreciation of intrinsic properties of semiconductors focusing on the optical properties of the material
To familiarise with the basic principles of optoelectronic devices (light emitting diode, laser, photodetector and photovoltaic).
To state the materials issues, requirements and selection for a given optoelectronic devices

15. Introduction to Optoelectronics - Lights
Lecture 1

16. Lights- Newton and Huygens
Lights as wave?
Lights as particles?
Huygens
They did not agree
with each other!
Newton

17. Lights – Einstein and Planck
1905 Einstein –related wave and particle properties of light
Planck - WAVE-PARTICLES DUALITY
E = h
Total E of the Photon (particle side)
Frequency (wave side)
Light is emitted in multiples of a certain minimum energy unit. The size of the unit – photon.
Explain the photoelectric effect - electron can be emitted if light is shone on a piece of metal
Energy of the light beam is not spread but propagate like particles e

18. Photons
When dealing with events at an atomic scale it is often best to regard light as composed of particles – photon. Forget it being wave.
A quanta of light
Electromagnetic radiation quantized and occurs in finite "bundles" of energy = photons
The energy of a single photon is given, in terms of its frequency, f, or wavelength, , as,
Eph = hf = hc/

19. Maxwell – Electromagnetic wave

20. Light as Electromagnetic Wave
Light as an electromagnetic wave is characterised by a combinations of time-varying electric field () and magnetic field (H) propagating through space.
Maxwell showed both  and H satisfy the same partial differential equation:
Changes in the fields propagate through space with speed c.

21. Speed of Light, c
Frequency of oscillation, of the fields and their wavelength, o in vacuum are related by;
c = o
In any other medium the speed, v is given by;
v= c/n = 
n = refractive index of the medium
 = wavelength in the medium
And,
r = relative magnetic permeability of the medium
r = relative electric permittivity of the medium
The speed of light in a medium is related to the electric and magnetic properties of the medium, and the speed of light can be expressed

22. Question 1
Relate Planck’s Equation (E = h) with the Speed of Light in a medium (c = )
h = Planck’s constant = eV
c = Speed of light = x 108 ms-1
Why do you think this equation is important when designing a light transmission devices based on semiconductor diodes?
Relate this with Photon Energy.

23. Particles: photon energy
Answer 1
E = hc 
Particles: photon energy
Wave-like properties

24. Answer 1 = 1.24x 10-6 /E Wavelength Energy Associated with colours
Each colour has energy associated with it

25. Question 2
Based on the equation you have produced in question 1, calculate the photon energy of violet, blue, green, orange and red lights. 

26. Electromagnetic Spectrum
Shorter wavelength
Answer 2:
Larger Photon Energy (eV)
V ~ 3.17eV
B ~ 2.73eV
G ~ 2.52eV
Y ~ 2.15eV
O ~ 2.08eV
R ~ 1.62eV
Longer wavelength

27. Spectral Response of Human Eyes
Visible Lights
Lights of wavelength detected by human eyes ~ 450nm to 650nm is called visible light:
3.1eV
1.8eV
Human eyes can detect lights with different colours
Each colour is detected with different efficiency.
Spectral Response of Human Eyes
Efficiency, 100%
400nm
500nm
600nm
700nm

28. Semi-transparent material
Interaction Between Light and Bulk Material 3c
Semi-transparent material
Incident light 4
1- Refraction
2- Transmission
3a – Specular reflection
3b – Total internal reflection
3c – Diffused reflection
4 – Scattering
There is also dispersion –where different colours bend differently 1 3a 3b 2

30. Appearance of insulator, metal and semiconductor
Appearance in term of colour depends on the interaction between the light with the electronics configuration of the material.
Normally,
High resistiviy material: insulator  transparent
High conductivity material: metals  metallic luster and opaque
Semiconductors  coloured, opaque or transparent, colour depending on the band gap of the material
For semiconductors the energy band diagram can explain the appearance of the material in terms of lustre and colouration

31. Question 3. Why is Silicon Black and Shiny?

32. Answer 3. Need to know, the energy gap of Si
Egap = 1.2eV
Need to know visible light photon energy
Evis ~ 1.8 – 3.1eV
Evis is larger than Silicon Egap
All visible light will be absorbed
Silicon appears black
Why is Si shiny?
A lot of photons absorption occurs in silicon, there are significant amount of electrons on the conduction band. These electrons are delocalized which induce the lustre and shines.

33. Question 4. Why is GaP yellow?

34. Answer 4 Need to know the Egap of GaP Egap = 2.26eV
Equivalent to  = 549nm.
E photons with h > 2.26ev absorb light (i.e. green, blue and violet)
E photons with h < 2.26eV transmit light (i.e. yellow, orange and red).
Sensitivity of human eye is greater for yellow than red therefore GaP appears yellow/orange.

35. Colours of Semiconductors
Evis= 1.8eV eV
I B G Y O R
If Photon Energy, Evis > Egap  Photons will be absorbed
If Photon Energy, Evis < Egap  Photons will transmitted
If Photon Energy is in the range of Egap ;
Those with higher energy than Egap will be absorbed.
We see the colour of the light being transmitted
If all colours are transmitted = White

36. Why do you think glass is transparent?
Glass is insulator (huge band gap)
The electrons find it hard to jump across a big energy gap (Egap >> 5eV)
Egap >> E visible spectrum ~ eV
All colored photon are transmitted, no absorption hence light transmit – transparent.
Defined transmission and absorption by Lambert’s law:
I = Io exp (- l)
I = incident beam
Io = transmitted beam
 = total linear absorption coefficient (m-1)
 = takes into account the loss of intensity from both scattering centers and absorption centers.
 = approaching zero for pure insulator.

37. What happens during photon absorption process?
Photon interacts with the lattice
Photon interacts with defects
Photon interacts with valance electrons

38. Absorption spectrum of a semiconductor.
Absorption Process of Semiconductors
Absorption coefficient (), cm-1
Photon energy (eV)
Absorption spectrum of a semiconductor.
Vis
Eg ~ vis
Wavelength (m) IR UV
Important region:

39. Absorption – an important phenomena in describing optical properties of semiconductors
Light, being a form of electromagnetic radiation, interacts with the electronic structure of atoms of a material.
The initial interaction is one of absorption; that is, the electrons of atoms on the surface of a material will absorb the energy of the colliding photons of light and move to the higher-energy states.
The degree of absorption depends, among other things, on the number of free electrons capable of receiving this photon energy.

40. Absorption Process of Semiconductors
The interaction process is a characteristic of a photon and depends on the energy of the photon (see the pervious slide – the x-axis).
Low-energy photons interact principally by ionization or excitation of the outer orbitals in solids’ atoms.
Light is composed of low-energy photons (< 10 eV) represented by infrared (IR), visible light, and ultraviolet (UV) in the electromagnetic spectrum.
High-energy protons (> 104 eV) are produced by x-rays and gamma rays.
The minimum photon energy required to excite and/or ionize the component atoms of a solid is called the absorption edge or threshold.

41. Valance-Conduction-Absorption
Process requires the lowest E of photon to initiate electron jumping (excitation)
EC-EV = h
EC-EV = Egap
If h > Egap then transition happens
Electrons in the conduction band and excited.
Conduction band, EC
Ephoton h
Egap
Valance band, EV

42. After the absorption then what?
Types  Direct and Indirect photon absorption
For all absorption process there must be:
Conservation of energy
Conservation of momentum or the wavevector
The production of e-h pairs is very important for various electronics devices especially the photovoltaic and photodetectors devices.
The absorbed light can be transformed to current in these devices

43. h = EC(min) - Ev (max) = Egap Conservation of wavevector
Direct Band Gap
K (wave number) h
Conservation of E
h = EC(min) - Ev (max) = Egap
Conservation of wavevector
Kvmax + photon = kc E
Direct vertical transition
Momentum of photon is negligible

44. Indirect Band Gap E
K (wave number) h

45. Question 5.
For indirect band gap transition, how do the energy and momentum or the wavevector are being conserved?

46. Answer Question 5 yourself

47. Refraction, Reflection and Dispersion Defines by refractive index; n
Light when it travels in a medium can be absorbed and reemitted by every atom in its path.
High n
Small n
n1 = refractive index of material 1
n2 = refractive index of material 2
Defines by refractive index; n

48. Total Internal Reflection

49. Mechanism and Application of TIR
Optical fibre for communication
What sort of materials do you think are suitable for fibre optics cables?

50. End Read EBB424 notes