Quantum Dots for Optoelectronic Devices - Phdassistance
                     Quantum Dots
for Optoelectronic 
 Devices
An Academic presentation by
Dr. Nancy Agnes, Head, Technical Operations, 
Phdassistance  Group www.phdassistance.com
Email: [email protected]
TODAY'S 
DISCUSSION
Outlin
e Introduction
Research advancements in quantum dots  
Future scope
INTRODUCTIO
NNanometre-scale semiconductor chips have been  
imagined as n ext-generation technology with high 
 functionality and convergence.
Quantum dots, also known as artificial atoms,  
have special properties owing to their quantum  
confinement in all three dimensions.
Quantum dots have a lot of interest in  
optoelectronic systems because of their special  
properties.
Contd...
Many attempts have been made worldwide to improve the  
efficiency and functionality of these promising nanomaterials for  
next-generation optoelectronic devices like lasers,  
photodetectors, amplifiers, and solar cells.
Quantum dot devices with outstanding performance surpassing 
 prior devices have been demonstrated by producing  
optoelectronic devices based on quantum dots over the last two 
 decades.
The progress in quantum dots for optoelectronic devices has  
been described in this article over the last few years.
RESEARCH ADVANCEMENTS 
IQNUANTUM 
DOFTorS decades, self-assembled nanostructures have  
been a t opic of considerable concern and 
significance.
By shrinking the dimensions of a semiconductor to a  
nanoscale, certain special properties, such as  
quantum effects, can be obtained.
The electrical and optical properties of  nanometre-
bsyizemd asneimpuiclaotnindgucttohresi rcamn obrep hmoalongipyu, lated to
qthuaannktsum scale effect. the
Cont
d...
Semiconductor quantum dots (QDs), similar to electrons, are a fascinating nanoscale  
structure of confined carriers in all dimensions.
Compared to conventional bulk semiconductors, 0D semiconductor nanostructures are  
more tuneable and sensitive to external parameters.
Furthermore, since QDs are zero-dimensional, they have distinct energy levels and a  
density of states that can be reduced to a set of delta functions.
Low-dimensional semiconductors have gained a lot of interest because of
their  fundamental advantages.
Contd...
This can be observed in the 1970 s; Dingle and Henry discovered 
quantum- organized semiconductor lasers could achieve  
tunabil i ty and threshold reduct ion [ 1 ] , which was later wavelength 
demonstrated in the 1980 s by Asada et al. and Arakawa et al.  [ 2 ] .
theoret ical ly
Since there was no feasible fabrication technique for QDs for several  
years after these pioneering works , the efforts dedicated to QDs and  
their implementat ions in devices were only experimental  research.
Due to major advancements in epitaxial d evelopment techniques,  self- 
assembled QDs were impossible to make unti l the early 1990 s.
Contd...
After self- assembled QDs were successful ly fabricated,  
laser diodes based on QDs running at 77 K were quickly  
developed.
Following the good demonstrat ion of self- assembled QDs  
and the f i rst QD laser, a worldwide init iat ive was  launched 
to improve QD growth control and manufacture  high- 
performance laser chips .
The m aj ority of research on self- assembled QDs focuses  
on material structures with mismatched latt ices, such as  
In( Ga) As/ Ga As [ 3 ] and In As/ In P [ 4 ] .
Contd...
Thermodynamic arguments are often used to explain
heteroepi taxia l  growth modes in thin f i lms.
The improvement made in QD self- assembly was quickly rewarded.
Quantum dot infrared photodetectors ( QDIPs) [ 3 ] , quantum
dot solar  cells ( QDSCs) [ 5 ] , quantum dot superluminescent
diodes ( QDSLDs)
[ 6 ] , and quantum dot ampl i f iers [ 7 ]
have al l been documented, in  addit ion to
lasers.
The invention of mid- wavelength and long- wavelength infrared
photodetectors [ 5 ]was prompted by inter- subband absorpt ion in
QDs  in the late 1990 s.
Contd...
Several groups publ ished QDSCs, quantum dot ampl i f iers ,
and  QDSLDs in the 2000 s.
The work on optimizing mater ia l growth and product archi tecture
is  sti l l going on to deliveron the promise
of high- performance QD
optoelectronic products.
As seen in f igure 1 , the threshold current density of QD
lasers has  recent ly reached the highest value for QW
lasers produced for many  decades.
Figure 1. The record threshold current densities at the time of publication can be seen in the historical history of heterostructure lasers [8].
FUTURE 
SCSOincPe Ethese nanostructures were first grown and 
 categorized, self-organized quantum dot
optoelectronic devices have come a long way.
Quantum dot lasers are now on par with  
quantum well lasers in terms of efficiency.
Inter-sublevel instruments, which can be used 
 as light sources and detectors and can operate
in a surface-normal mode, have increased 
 efficiency and special properties.
Contd...
Quantum dot optoelectronic sensors are expected to play a major role in upcoming systems.  
High-performance QDIPs are also possible thanks to the intensive research activities in QDs.
QDIPs have basic benefits over Quantum Well Infrared Photodetector (QWIP) in that they 
 can run at higher temperatures and have lower dark current.
QDIPs are now outperforming QWIPs in terms of efficiency. QDIPs have outperformed 
 QWIPs in terms of operating temperature.
Several issues remain, such as inadequate quantum performance, and QDIP architecture 
 and fabrication must be enhanced to realize their potential in third-generation infrared  
sensing.
Contd...
QDIPs with efficiency comparable to existing s tate-of-the-art technologies such as 
QWIPs  and HgCdTe photodetector may be used in the coming years.
Due to various fundamental shortcomings, such as QDs' slow absorption and the extreme 
 thermal connection between the intermediate and conduction bands, QDSCs are the 
least  evolved of the various forms of QD optoelectronic systems.
Further advances in device physics, design, growth, and characterization of QDSCs would 
 be needed to achieve high conversion efficiency beyond the record value of GaAs single- 
 junction solar cells.
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