Quantum Dotsfor Optoelectronic DevicesAn Academic presentation byDr. Nancy Agnes, Head, Technical Operations, Phdassistance Group www.phdassistance.comEmail: info@phdassistance.com

Outline

TODAY'S DISCUSSION

Introduction

Research advancements in quantum dots

Future scope

INTRODUCTIONNanometre-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.

For 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-sized semiconductors can be manipulatedby manipulating their morphology,

thankstothequantum scale effect.

RESEARCH ADVANCEMENTS INQUANTUM DOTS

Contd...

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 oftheir fundamental advantages.

Contd...

This can be observed in the 1970 s; Dingle and Henryquantum- organized semiconductor lasers could achievetunabil i ty and threshold reduct ion [ 1 ] , which was later

discovered wavelength theoret ical ly

demonstrated in the 1980 s by Asada et al. and Arakawa et al. [ 2 ] .

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 explainheteroepi 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 ] , quantumdot 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 tolasers.

The invention of mid- wavelength and long- wavelength infraredphotodetectors [ 5 ]was prompted by inter- subband absorpt ion inQDs 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 opt imizing mater ia l growth and product archi tectureis sti l l going on to deliveron the promiseof high- performance QDoptoelectronic products.

As seen in f igure 1 , the threshold currentdensity of QD lasers has recent ly reached thehighest 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 SCOPESince these nanostructures were first grown and categorized, self-organized quantum dotoptoelectronic 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 operatein 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.

CONTACT USUNITED KINGDOM+44 7537144372

INDIA+91-9176966446

EMAILinfo@phdassistance.com