We report a novel GaN/InGaN LED endowed with rectangular shaped multiple quantum wells and gradual narrowing of the bandgap of electron blocking layer (EBL) towards the anode side and subsequently analyze the obtained results through well-calibrated numerical simulation in APSYS. The results show that the droop in internal quantum efficiency (IQE) for the proposed LED decreases to 11% as compared to 54%, obtained in conventional structure. Additionally, while operated at 150&nbsp;mA the proposed LED provides an output power that is enhanced by 80% more than what is obtained in conventional LED. The analysis reveals that the gradual change in Al content of EBL layer helps scale down the electric field produced in this region due to polarization which in turn imposes strong blocking on the electrons that try to escape out the active region and move to EBL layer. Moreover, due to less amount of downward valence band bending better hole injection takes place in the active region. Consequently the proposed structure allows increased electron and hole concentrations in the multiple quantum wells thereby enhancing its internal quantum efficiency while a large current flows through the device. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.

ABHIJIT BISWAS

Radio Physics and Electronics

M SAHA

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Microsystem Technologies

This work analyzes the effect of incorporating a shallow first well and a two-step electron-blocking layer (EBL) on the performance of an InGaN/GaN rectangular multiple quantum well LED using well-calibrated numerical simulator SILVACOATLAS. The results show 78% improvement in output power of the proposed LED structure in comparison with the conventional structure at 150 mA injection current. In addition, the droop in internal quantum efficiency (IQE) for the proposed LED structure reduces to 29% from 54% which is observed in conventional structure. The simulation study reveals that the shallow first well facilitates to reduce the effective blocking provided by the preceding GaN layer to the injected electrons, thereby increasing the electron injection. In addition, the stepped electron-blocking layer raises the energy barrier for electrons at the EBL causing better confinement of electrons compared to conventional structure. The stepped EBL also decreases the effective energy barrier for holes significantly, thereby aiding better injection of holes into the multiple quantum well light-emitting region. Consequently, carrier concentrations in the active region of the proposed structure increase, thereby enhancing its output power at high input current. © 2017, Springer Nature Singapore Pte Ltd.

Lecture Notes in Electrical Engineering

Enhanced performance of GaN/InGaN multiple quantum well LEDs by shallow first well and stepped electron-blocking layer

We propose a phosphor-free dual wavelength monolithic white LED comprising a tunnel junction that separates a yellow light-emitting InGaN/GaN multiple quantum well (MQW) structure without an electron blocking layer (EBL) from a blue light-emitting MQW structure. Using a well-calibrated APSYS simulation software we investigate its performance in terms of output power, wall plug efficiency, and CIE plot of the emitted light and analyze its operation on the basis of band diagram, carrier distribution, EL spectra and radiative recombination rate taking into account the carrier confinement and carrier reuse effects due to removal of an EBL and incorporation of a tunnel junction, respectively. At the injection current density of 250 A/cm2, our proposed white LED exhibits 232% improvement in output power as compared to a conventional blue LED and only 40% droop reduction of wall plug efficiency as opposed to 56% in a reported white LED. The Commission Internationale de l'Eclairage (CIE) coordinates of the emitted light from the proposed white LED structure are found to be (0.310, 0.309) at 100 A/cm2 which signify a good quality white light emission. © 2018 Elsevier B.V.

Optical Materials

Monolithic high performance InGaN/GaN white LEDs with a tunnel junction cascaded yellow and blue light-emitting structures

We design and evaluate the performance of three InGaN/GaN multiple quantum well blue LEDs – A. rectangular quantum wells with a fixed barrier width, B. trapezoidal quantum wells with a fixed barrier width, and C. trapezoidal quantum wells with a decreasing barrier width towards the anode end – in terms of efficiency droop and power output. We obtain band diagram, electric field, emission spectra and carrier concentration using well calibrated APSYS simulation. Use of trapezoidal quantum wells increases better overlapping between electron and hole wavefunctions thereby increasing radiative recombination events. Furthermore decreasing barrier width from n- to p- regions shortens hole transport path which results in better hole transport and distribution in the wells and hence larger radiative recombination rate. Our proposed structure C exhibits efficiency droop reduction of 2.1% and enhancement of optical power of 236.7% compared to conventional rectangular quantum well structure at injection current of 120 mA. © 2017 Elsevier B.V.

Optics Communications

Improved performance of InGaN/GaN MQW LEDs with trapezoidal wells and gradually thinned barrier layers towards anode

In this work, we propose and investigate numerically InGaN/GaN based multiple quantum well (QW) blue light-emitting diodes (LEDs) with step quantum well (InGaN)/barrier (GaN) structures. We design four LED structures—(LED-A) InGaN/GaN rectangular quantum well, (LED-B) one down step in the middle of the QW created using sharp increase in In contents, (LED-C) one down step in the middle of the QW and the other down step in the right barrier away from QW and (LED-D) similar to LED-C barring one down step in the left barrier facing the QW. Using well-calibrated APSYS simulation program we compare the variation of output power and internal quantum efficiency of LEDs with input injection current and analyze them in the light of energy band diagram, electric field distribution, carrier concentration and radiative recombination rate. The proposed LED-D exhibits significant improvement in optical output power ~ 180.7% compared to conventional LED-A. Furthermore unlike other three LED structures, LED-D shows a very low internal quantum efficiency droop of 5.1% only at injection current of 120 mA. © 2017 Springer-Verlag GmbH Germany

Journal	Data powered by TypesetMicrosystem Technologies
Publisher	Data powered by TypesetSpringer Verlag
ISSN	0946-7076
Open Access	No