Upload
bilu-paul
View
226
Download
0
Embed Size (px)
Citation preview
8/6/2019 Semiconductor Lasers Leture 12-01-09
1/34
Semiconductor lasers
by: Khanh Kieu
(12/01/2009)
8/6/2019 Semiconductor Lasers Leture 12-01-09
2/34
Outlines
Introduction
Semiconductor laser: basics
Types of semiconductor laser
High power semiconductor lasers
Applications of semiconductor lasers
8/6/2019 Semiconductor Lasers Leture 12-01-09
3/34
Introduction
Laserfocusworld.com
8/6/2019 Semiconductor Lasers Leture 12-01-09
4/34
Introduction
First demonstration in 1962 by Robert N. Hall(homojunction diodes)
8/6/2019 Semiconductor Lasers Leture 12-01-09
5/34
Introduction
First CW laser diode operatingat room temperature wasdemonstrated in 1970 byZhores Alferov(Double heterostructure )
8/6/2019 Semiconductor Lasers Leture 12-01-09
6/34
Semiconductor laser: doping
As Ga As
SeGa
As As
Ga
Ga
e
As Ga As
ZnGa
As As
Ga
Ga
h
n-doped p-doped
8/6/2019 Semiconductor Lasers Leture 12-01-09
7/34
p-n junction
http://upload.wikimedia.org/wikipedia/commons/4/48/PnJunction-PV-E.PNG8/6/2019 Semiconductor Lasers Leture 12-01-09
8/34
Homojunction diode laser
p+ n+
EF n
(a)
Eg
Ev
Ec
Ev
Holes in VB
Electrons in CB
Junction
ElectronsE
c
p+
Eg
V
n+
(b)
EF n
eV
EF p
The energy band diagram of a degenerately dopedp-n with no bias. (b) Banddiagram with a sufficiently large forward bias to cause population inversion andhence stimulated emission.
Inversionregion
EF p
Ec
Ec
eVo
1999 S.O. Kasap, Optoelectronics (Prentice Hall)
8/6/2019 Semiconductor Lasers Leture 12-01-09
9/34
Homojunction diode laser
Population Inversion: More electrons in the CB at energiesnear Ec than electrons in VB near Ev
The region where the population inversion occurs develops alayer along the junction called an inversion layeror activeregion
8/6/2019 Semiconductor Lasers Leture 12-01-09
10/34
Homojunction diode laser
LElectrode
Current
GaAs
GaAsn+
p+
Cleaved surface mirror
Electrode
Active region(stimulated emission region)
A schematic illustration of a GaAs homojunction laserdiode. The cleaved surfaces act as reflecting mirrors.
L
1999 S.O. Kasap, Optoelectronics (Prentice Hall)
An adequate forward bias is
required to inject carriersacross the junction toinitiate population inversionThe process is calledinjection pumping.
8/6/2019 Semiconductor Lasers Leture 12-01-09
11/34
Homojunction diode laser
Typical output optical power vs. diode current (I) characteristics and the correspondingoutput spectrum of a laser diode.
Laser
LaserOptical Power
Optical Power
I0
LEDOptical Power
Ith
Spontaneous
emission
Stimulated
emission
Optical Power
1999 S.O. Kasap, Optoelectronics (Prentice Hall)
8/6/2019 Semiconductor Lasers Leture 12-01-09
12/34
Homojunction diode laser
The drawback of a homojunction diode laser is the high thresholdcurrent density therefore it is restricted to operating at very lowtemperatures or pulsed mode
1000 A/cm2 at 77 K temperatures
100 000 A/cm2 at 300 K temperatures
Solution Double heterostructure laser
8/6/2019 Semiconductor Lasers Leture 12-01-09
13/34
Double heterostructure diode laser
1. Carrier confinement:Confine the injected electrons and holesto a narrow region about the junction. This requires less currentto establish the required concentration of electrons for
population inversion.
2. Photon confinement:Construct a dielectric waveguide aroundthe optical gain region to increase the photon concentration andelevate the probability of stimulated emission. This reduces thenumber of electrons lost traveling off the cavity axis.
8/6/2019 Semiconductor Lasers Leture 12-01-09
14/34
Double heterostructure diode laser
Refractiveindex
Photondensity
Active
region
n ~ 5%
2 eV
Holes in VB
Electrons in CB
AlGaAsAlGaAs
1.4 eV
Ec
Ev
Ec
Ev
(a)
(b)
pn p
Ec
(a) A doubleheterostructure diode hastwo junctions which arebetween two differentbandgap semiconductors(GaAs and AlGaAs).
2 eV
(b) Simplified energy
band diagram under alarge forward bias.Lasing recombinationtakes place in the p-GaAs layer, theactive layer
(~0.1 m)
(c) Higher bandgapmaterials have a
lower refractiveindex
(d) AlGaAs layersprovide lateral opticalconfinement.
(c )
(d)
1999 S.O. Kasap, Optoelectronics (Prentice Hall)
GaAs
8/6/2019 Semiconductor Lasers Leture 12-01-09
15/34
Double heterostructure diode laser
Heterostructure
Monostructure
8/6/2019 Semiconductor Lasers Leture 12-01-09
16/34
Double heterostructure diode laser
1. Due to the thin p-GaAs layer a minimal amount of current is requiredto increase the concentration of injected carriers. This is how thethreshold current for population inversion and optical gain is reduced
2. The semiconductor with a wider bandgap (AlGaAs) will also have alower refractive index than GaAs. This difference in refractive index iswhat establishes an optical dielectric waveguide that ultimatelyconfines photons to the active region
8/6/2019 Semiconductor Lasers Leture 12-01-09
17/34
Double heterostructure diode laser
Schematic illustration of the the structure of a double heterojunction stripecontact laser diode
Oxide insulator
Stripe electrode
SubstrateElectrode
Active region where J>Jth.
(Emission region)
p-GaAs (Contacting layer)
n-GaAs (Substrate)
p-GaAs (Active layer)
Current
paths
L
W
Cleaved reflecting surfaceEllipticallaser
beam
p-AlxGa
1-xAs (Confining layer)
n-AlxGa
1-xAs (Confining layer)
12 3
Cleaved reflecting surface
Substrate
1999 S.O. Kasap, Optoelectronics (Prentice Hall)
8/6/2019 Semiconductor Lasers Leture 12-01-09
18/34
Types of semiconductor lasers
Quantum well lasers
Quantum cascade lasers
Distributed feedback lasers
External-cavity diode lasers
VCSELs
VECSELs
OPSELs
8/6/2019 Semiconductor Lasers Leture 12-01-09
19/34
DFB semiconductor lasers
8/6/2019 Semiconductor Lasers Leture 12-01-09
20/34
External-cavity diode lasers
http://www.rp-photonics.com
Widely tunable single frequency laser
8/6/2019 Semiconductor Lasers Leture 12-01-09
21/34
OPSELs
(Credit: D. Payne)
Y. Kaneda at OSC
E i i l h f i
8/6/2019 Semiconductor Lasers Leture 12-01-09
22/34
Emission wavelengths of various
types of laser diodes
http://www.rp-photonics.com
8/6/2019 Semiconductor Lasers Leture 12-01-09
23/34
High power diode lasers
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
24/34
High power diode lasers
Ralf Ostendorf, Fraunhofer Institute
8/6/2019 Semiconductor Lasers Leture 12-01-09
25/34
Stacked-bar diode laser
Newport illustration
Laserline, GmbH, Germany
8/6/2019 Semiconductor Lasers Leture 12-01-09
26/34
Stacked-bar diode laser
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
27/34
Diode laser: Applications
Telecommunication
Data storage
Material processing
Laser pumping
Medicine
Laser printers, bar-code readers
~ 1 Billion units sale per year!
8/6/2019 Semiconductor Lasers Leture 12-01-09
28/34
High power diode laser
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
29/34
Diode laser for pumping
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
30/34
Industrial applications
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
31/34
Industrial applications
Dilas photo
8/6/2019 Semiconductor Lasers Leture 12-01-09
32/34
Industrial applications
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
33/34
Medical applications
Credit: Jeff Hecht
8/6/2019 Semiconductor Lasers Leture 12-01-09
34/34
Thank you!