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10 pages, 397 KiB

Open AccessArticle

A Unified Pervasive Linebroadening Function for Quantum Wells in Light Emitting Diodes

by Juha Viljanen

Appl. Sci. 2020, 10(11), 3774; https://doi.org/10.3390/app10113774 - 29 May 2020

Cited by 2 | Viewed by 1675

Abstract

The broadening functions for quantum wells in LEDs and laser diodes below the lasing threshold are examined. Inhomogeneous and homogeneous broadening mechanisms are included. Hydrogen-atom-like exciton and the electron-hole plasma recombination models are considered. Material disorder and the Urbach tail are reviewed as [...] Read more.

The broadening functions for quantum wells in LEDs and laser diodes below the lasing threshold are examined. Inhomogeneous and homogeneous broadening mechanisms are included. Hydrogen-atom-like exciton and the electron-hole plasma recombination models are considered. Material disorder and the Urbach tail are reviewed as the main reasons for the inhomogeneous broadening. Charge carrier scattering and relaxation times in the conduction and valence bands are examined as the origin for the homogeneous lifetime broadening. Two homogeneous lineshapes are compared using the momentum relaxation times obtained from the electron and hole mobilities available for GaAs. In addition to crystal disorder, the mutual collision of charge carriers in the quantum wells is examined as the reason for the relaxation time shortening. The analogy to pressure broadening in gases is used to combine the proper homogeneous and inhomogeneous broadening functions to a unified quantum well lineshape. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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14 pages, 2926 KiB

Open AccessArticle

Fluorene–Triphenylamine-Based Bipolar Materials: Fluorescent Emitter and Host for Yellow Phosphorescent OLEDs

by Ramanaskanda Braveenth, Hasu Jung, Keunhwa Kim, Bo Mi Kim, Il-Ji Bae, Miyoung Kim and Kyu Yun Chai

Appl. Sci. 2020, 10(2), 519; https://doi.org/10.3390/app10020519 - 10 Jan 2020

Cited by 5 | Viewed by 3557

Abstract

In this study, two new bipolar materials were designed and synthesized: N¹-(9,9-diphenyl-9H-fluoren-2-yl)-N¹-(4,6-diphenylpyrimidin-2-yl)-N⁴,N⁴-diphenylbenzene-1,4-diamine (FLU-TPA/PYR) and N¹-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-N¹-(9,9-diphenyl-9H-fluoren-2-yl)-N⁴,N⁴ diphenylbenzene-1,4-diamine (FLU-TPA/TRZ). We [...] Read more.

In this study, two new bipolar materials were designed and synthesized: N¹-(9,9-diphenyl-9H-fluoren-2-yl)-N¹-(4,6-diphenylpyrimidin-2-yl)-N⁴,N⁴-diphenylbenzene-1,4-diamine (FLU-TPA/PYR) and N¹-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-N¹-(9,9-diphenyl-9H-fluoren-2-yl)-N⁴,N⁴ diphenylbenzene-1,4-diamine (FLU-TPA/TRZ). We fabricated two different devices, namely a yellow phosphorescent organic light-emitting diode (PhOLED) and a non-doped fluorescent OLED emitter with both FLU-TPA/PYR and FLU-TPA/TRZ. The FLU-TPA/PYR host-based yellow PhOLED device showed better maximum current, power and external quantum efficiencies at 21.70 cd/A, 13.64 lm/W and 7.75%, respectively. The observed efficiencies were better than those of the triazine-based FLU-TPA/TRZ. The non-doped fluorescent device with the triazine-based FLU-TPA/TRZ material demonstrated current, power and external quantum efficiencies of 10.30 cd/A, 6.47 lm/W and 3.57%, respectively. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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24 pages, 3845 KiB

Open AccessFeature PaperArticle

Calibration of Polarization Fields and Electro-Optical Response of Group-III Nitride Based c-Plane Quantum-Well Heterostructures by Application of Electro-Modulation Techniques

by Dimitra N. Papadimitriou

Appl. Sci. 2020, 10(1), 232; https://doi.org/10.3390/app10010232 - 27 Dec 2019

Cited by 4 | Viewed by 2914

Abstract

The polarization fields and electro-optical response of PIN-diodes based on nearly lattice-matched InGaN/GaN and InAlN/GaN double heterostructure quantum wells grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy were experimentally quantified. Dependent on the indium content and the applied voltage, an intense [...] Read more.

The polarization fields and electro-optical response of PIN-diodes based on nearly lattice-matched InGaN/GaN and InAlN/GaN double heterostructure quantum wells grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy were experimentally quantified. Dependent on the indium content and the applied voltage, an intense near ultra-violet emission was observed from GaN (with fundamental energy gap E_g = 3.4 eV) in the electroluminescence (EL) spectra of the InGaN/GaN and InAlN/GaN PIN-diodes. In addition, in the electroreflectance (ER) spectra of the GaN barrier structure of InAlN/GaN diodes, the three valence-split bands, Γ₉, Γ₇₊, and Γ₇₋, could selectively be excited by varying the applied AC voltage, which opens new possibilities for the fine adjustment of UV emission components in deep well/shallow barrier DHS. The internal polarization field E_pol = 5.4 ± 1.6 MV/cm extracted from the ER spectra of the In_0.21Al_0.79N/GaN DHS is in excellent agreement with the literature value of capacitance-voltage measurements (CVM) E_pol = 5.1 ± 0.8 MV/cm. The strength and direction of the polarization field E_pol = −2.3 ± 0.3 MV/cm of the (0001) In_0.055Ga_0.945N/GaN DHS determined, under flat-barrier conditions, from the Franz-Keldysh oscillations (FKOs) of the electro-optically modulated field are also in agreement with the CVM results E_pol = −1.2 ± 0.4 MV/cm. The (absolute) field strength is accordingly significantly higher than the E_pol strength quantified in published literature by FKOs on a semipolar

(11 \bar{2} 2)

oriented In_0.12Ga_0.88N quantum well. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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18 pages, 5380 KiB

Open AccessArticle

Disturbances Generated by Lighting Systems with LED Lamps and the Reduction in Their Impacts

by Łukasz Putz, Karol Bednarek and Ryszard Nawrowski

Appl. Sci. 2019, 9(22), 4894; https://doi.org/10.3390/app9224894 - 14 Nov 2019

Cited by 15 | Viewed by 5724

Abstract

The paper deals with electromagnetic disturbances in the form of current higher harmonics, which are generated by LED lighting elements. It presents the problems related to the formation and impact of higher harmonics in the electrical systems of commercial facilities. The results of [...] Read more.

The paper deals with electromagnetic disturbances in the form of current higher harmonics, which are generated by LED lighting elements. It presents the problems related to the formation and impact of higher harmonics in the electrical systems of commercial facilities. The results of tests and analyses of current distortions for two different LED lamps are included, and these are in reference to the parameters set out in the normal applicable standards. A system was then proposed to improve the quality of energy in the mains of commercial facilities in the form of a two-stage power supply. Tests of the systems with the aforementioned LED lamps were conducted and commented upon after introduction of the two-stage power supply. The final part of the paper contains a summary of the obtained test results. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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8 pages, 1705 KiB

Open AccessArticle

An Ultra-High-SMSR External-Cavity Diode Laser with a Wide Tunable Range around 1550 nm

by Yan Wang, Hao Wu, Chao Chen, Yinli Zhou, Yubing Wang, Lei Liang, Zhenhua Tian, Li Qin and Lijun Wang

Appl. Sci. 2019, 9(20), 4390; https://doi.org/10.3390/app9204390 - 17 Oct 2019

Cited by 8 | Viewed by 2977

Abstract

In this paper, a widely tunable external cavity diode laser (ECDL) with an ultra-high side mode suppression ratio (SMSR) was fabricated. Three configurations were constructed to investigate the relationship between the grating features and the SMSR. When a 1200 grooves/mm grating with a [...] Read more.

In this paper, a widely tunable external cavity diode laser (ECDL) with an ultra-high side mode suppression ratio (SMSR) was fabricated. Three configurations were constructed to investigate the relationship between the grating features and the SMSR. When a 1200 grooves/mm grating with a first order diffraction efficiency of 91% is utilized in the external-cavity laser system, a maximum SMSR of 65 dB can be achieved. In addition, the tunable range reaches 209.9 nm. The results show that the laser performance can be improved by proper high grating groove number and first-order diffraction efficiency. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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10 pages, 724 KiB

Open AccessArticle

Properties of Phase Solitons in an Optically Driven Semiconductor Ring Laser

by Ghafour Hashemvand Shakarab, Reza Kheradmand, Mohammad Agha Bolorizadeh and Franco Prati

Appl. Sci. 2019, 9(20), 4351; https://doi.org/10.3390/app9204351 - 16 Oct 2019

Cited by 2 | Viewed by 1815

Abstract

A semiconductor ring laser with a long cavity supports propagating localised structures with a chiral charge, named phase solitons. In this paper we study the dependence of the velocity and of the duration of the phase solitons on the characteristic time scales of [...] Read more.

A semiconductor ring laser with a long cavity supports propagating localised structures with a chiral charge, named phase solitons. In this paper we study the dependence of the velocity and of the duration of the phase solitons on the characteristic time scales of the laser, namely the photon lifetime and the carrier lifetime. We show numerically that phase solitons are stable over a large range of those parameters and verify that the propagation velocity decreases linearly with the ratio of the carrier lifetime to the photon lifetime, while the duration is proportional to the ratio of the carrier lifetime to the cavity roundtrip time. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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11 pages, 1596 KiB

Open AccessArticle

Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

by Han-Youl Ryu, Geun-Hwan Ryu and Chibuzo Onwukaeme

Appl. Sci. 2019, 9(19), 4160; https://doi.org/10.3390/app9194160 - 03 Oct 2019

Cited by 5 | Viewed by 3211

Abstract

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the [...] Read more.

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be ~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the quantum well and the inhomogeneous carrier distribution in the MQWs. The difference in the internal electric field of the MQW between the LED on silicon and sapphire could be a major reason for the difference in the effective active volume, and consequently, the efficiency droop. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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8 pages, 1387 KiB

Open AccessCommunication

III-Nitride Multi-Quantum-Well Light Emitting Structures with Selective Carrier Injection

by Hussein S. El-Ghoroury, Mikhail V. Kisin and Chih-Li Chuang

Appl. Sci. 2019, 9(18), 3872; https://doi.org/10.3390/app9183872 - 15 Sep 2019

Cited by 1 | Viewed by 2541

Abstract

Incorporation into the multi-layered active region of a semiconductor light-emitting structure specially designed intermediate carrier blocking layers (IBLs) allows efficient control over the carrier injection distribution across the structure’s active region to match the application-driven device injection characteristics. This approach has been successfully [...] Read more.

Incorporation into the multi-layered active region of a semiconductor light-emitting structure specially designed intermediate carrier blocking layers (IBLs) allows efficient control over the carrier injection distribution across the structure’s active region to match the application-driven device injection characteristics. This approach has been successfully applied to control the color characteristics of monolithic multi-color light-emitting diodes (LEDs). We further exemplify the method’s versatility by demonstrating the IBL design of III-nitride multiple-quantum-well (MQW) light-emitting diode with active quantum wells uniformly populated at LED operational current. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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10 pages, 7075 KiB

Open AccessArticle

Light Extraction Enhancement of InGaN Based Micro Light-Emitting Diodes with Concave-Convex Circular Composite Structure Sidewall

by Lijun Tan, Quanbin Zhou, Wenlong Hu, Hong Wang and Ruohe Yao

Appl. Sci. 2019, 9(17), 3458; https://doi.org/10.3390/app9173458 - 21 Aug 2019

Cited by 4 | Viewed by 3663

Abstract

We demonstrate that the concave-convex circular composite structure sidewall prepared by inductively coupled plasma (ICP) etching is an effective approach to increase the light efficiency without deteriorating the electrical characteristics for micro light-emitting diodes (LEDs). The saturated light output power of the device [...] Read more.

We demonstrate that the concave-convex circular composite structure sidewall prepared by inductively coupled plasma (ICP) etching is an effective approach to increase the light efficiency without deteriorating the electrical characteristics for micro light-emitting diodes (LEDs). The saturated light output power of the device using the concave-convex circular composite structure sidewalls with a radius of 2 μm is 39.75 mW, an improvement of 7.2% compared with that of the device using flat sidewalls. The enhanced light output characteristics are primarily attributed to the increased photon emitting due by decreasing the total internal reflection without losing the active region area. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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10 pages, 2923 KiB

Open AccessArticle

Coherent Perfect Absorption Laser Points in One-Dimensional Anti-Parity–Time-Symmetric Photonic Crystals

by Huiling Wang, Weihao Kong, Pu Zhang, Zhongming Li and Dong Zhong

Appl. Sci. 2019, 9(13), 2738; https://doi.org/10.3390/app9132738 - 06 Jul 2019

Cited by 22 | Viewed by 3674

Abstract

We investigate the coherent perfect absorption laser points (CPA-LPs) in anti-parity–time-symmetric photonic crystals. CPA-LPs, which correspond to the poles of reflection and transmission, can be found in the parameter space composed of gain–loss factor and angular frequency. Discrete exceptional points (EPs) split as [...] Read more.

We investigate the coherent perfect absorption laser points (CPA-LPs) in anti-parity–time-symmetric photonic crystals. CPA-LPs, which correspond to the poles of reflection and transmission, can be found in the parameter space composed of gain–loss factor and angular frequency. Discrete exceptional points (EPs) split as the gain–loss factor increases. The CPA-LPs sandwiched between the EPs are proved to be defective modes. The localization of light field and the bulk effect of gain/loss in materials induce a sharp change in phase of the reflection coefficient near the CPA-LPs. Consequently, a large spatial Goos–Hänchen shift, which is proportional to the slope of phase, can be achieved around the CPA-LPs. The study may find great applications in highly sensitive sensors. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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13 pages, 2734 KiB

Open AccessArticle

Online Measurement of Internal Parameters in a Quasi-CW Diode-Pumped Nd:YAG Laser

by Wei Wang, Zhipeng Yan and Zaiyuan Wang

Appl. Sci. 2019, 9(12), 2547; https://doi.org/10.3390/app9122547 - 21 Jun 2019

Cited by 3 | Viewed by 2455

Abstract

We present a simple and practical online measurement method to estimate internal parameters (small-signal gain coefficient, internal optical losses, the saturation parameter, and transmittance of the coupling output mirror) in an neodymium doped yttrium aluminum garnet Nd:YAG laser system. A measurement cell, placed [...] Read more.

We present a simple and practical online measurement method to estimate internal parameters (small-signal gain coefficient, internal optical losses, the saturation parameter, and transmittance of the coupling output mirror) in an neodymium doped yttrium aluminum garnet Nd:YAG laser system. A measurement cell, placed in the optical cavity of a laser, consists of a polarizer and a rotatable polarization analyzer. Internal parameters are measured conveniently by introducing variable polarization reflective loss. Online measurements of the internal parameters in a quasi-continuous-wave (CW) diode-pumped Nd:YAG laser are performed and the measured results, which are discussed and analyzed, indicate good measurement accuracy. Experiments to investigate validity are conducted and further verify the applicability of the measurement method. A measurement cell with a small volume that is easy to access has potential to be used in the online measurement, optimized design, and maintenance of a laser. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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16 pages, 14699 KiB

Open AccessArticle

Linewidth Narrowing of Mutually Injection Locked Semiconductor Lasers with Short and Long Delay

by Weichao Ma, Bing Xiong, Changzheng Sun, Xu Ke, Jian Wang, Zhibiao Hao, Lai Wang, Yanjun Han, Hongtao Li, Jiadong Yu and Yi Luo

Appl. Sci. 2019, 9(7), 1436; https://doi.org/10.3390/app9071436 - 05 Apr 2019

Cited by 8 | Viewed by 4115

Abstract

A simple and effective approach to semiconductor laser linewidth narrowing via mutual injection locking is proposed and demonstrated in both short and long delay regimes. A theoretical analysis is presented to investigate the linewidth behavior of semiconductor lasers under mutual injection locking. Experimental [...] Read more.

A simple and effective approach to semiconductor laser linewidth narrowing via mutual injection locking is proposed and demonstrated in both short and long delay regimes. A theoretical analysis is presented to investigate the linewidth behavior of semiconductor lasers under mutual injection locking. Experimental demonstrations in short and long delay regimes are implemented by integrated devices and a fiber link system, respectively. Locking condition and dependence of laser linewidth on coupling parameters in both regimes are studied, confirming mutual injection locking as a practical method for linewidth narrowing. For the short-delayed integrated lasers, a linewidth narrowing factor of 13 is demonstrated and sub-MHz linewidth is achieved, while for the long-delayed lasers coupled by fiber link, the intrinsic linewidth is reduced to sub-100 Hz. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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Review

Jump to: Research

27 pages, 7625 KiB

Open AccessReview

Light Emitting Devices Based on Quantum Well-Dots

by Mikhail V. Maximov, Alexey M. Nadtochiy, Sergey A. Mintairov, Nikolay A. Kalyuzhnyy, Natalia V. Kryzhanovskaya, Eduard I. Moiseev, Nikita Yu. Gordeev, Yuriy M. Shernyakov, Alexey S. Payusov, Fedor I. Zubov, Vladimir N. Nevedomskiy, Sergei S. Rouvimov and Alexey E. Zhukov

Appl. Sci. 2020, 10(3), 1038; https://doi.org/10.3390/app10031038 - 04 Feb 2020

Cited by 41 | Viewed by 4635

Abstract

We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are formed by metalorganic vapor phase epitaxial deposition of 4–16 monolayers of In_xGa [...] Read more.

We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are formed by metalorganic vapor phase epitaxial deposition of 4–16 monolayers of In_xGa_1−xAs of moderate indium composition (0.3 < x < 0.5) on GaAs substrates and represent dense arrays of carrier localizing indium-rich regions inside In-depleted residual quantum wells. QWDs are intermediate in properties between 2D quantum wells and 0D quantum dots and show some advantages of both of those. In particular, they offer high optical gain/absorption coefficients as well as reduced carrier diffusion in the plane of the active region. Edge-emitting QWD lasers demonstrate low internal loss of 0.7 cm⁻¹ and high internal quantum efficiency of 87%. as well as a reasonably high level of continuous wave (CW) power at room temperature. Due to the high optical gain and suppressed non-radiative recombination at processed sidewalls, QWDs are especially advantageous for microlasers. Thirty-one μm in diameter microdisk lasers show a high record for this type of devices output power of 18 mW. The CW lasing is observed up to 110 °C. A maximum 3-dB modulation bandwidth of 6.7 GHz is measured in the 23 μm in diameter microdisks operating uncooled without a heatsink. The open eye diagram is observed up to 12.5 Gbit/s, and error-free 10 Gbit/s data transmission at 30 °C without using an external optical amplifier, and temperature stabilization is demonstrated. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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16 pages, 3237 KiB

Open AccessReview

Improved Charge Injection and Transport of Light-Emitting Diodes Based on Two-Dimensional Materials

by Yuanming Zhou, Sijiong Mei, Dongwei Sun, Neng Liu, Fei Mei, Jinxia Xu and Xianan Cao

Appl. Sci. 2019, 9(19), 4140; https://doi.org/10.3390/app9194140 - 03 Oct 2019

Cited by 5 | Viewed by 3831

Abstract

Light-emitting diodes (LEDs) are considered to be the most promising energy-saving technology for future lighting and display. Two-dimensional (2D) materials, a class of materials comprised of monolayer or few layers of atoms (or unit cells), have attracted much attention in recent years, due [...] Read more.

Light-emitting diodes (LEDs) are considered to be the most promising energy-saving technology for future lighting and display. Two-dimensional (2D) materials, a class of materials comprised of monolayer or few layers of atoms (or unit cells), have attracted much attention in recent years, due to their unique physical and chemical properties. Here, we summarize the recent advances on the applications of 2D materials for improving the performance of LEDs, including organic light emitting diodes (OLEDs), quantum dot light emitting diodes (QLEDs) and perovskite light emitting diodes (PeLEDs), using organic films, quantum dots and perovskite films as emission layers (EMLs), respectively. Two dimensional materials, including graphene and its derivatives and transition metal dichalcogenides (TMDs), can be employed as interlayers and dopant in composite functional layers for high-efficiency LEDs, suggesting the extensive application in LEDs. The functions of 2D materials used in LEDs include the improved work function, effective electron blocking, suppressed exciton quenching and reduced surface roughness. The potential application of 2D materials in PeLEDs is also presented and analyzed. Full article

(This article belongs to the Special Issue Novel and Efficient Semiconductor-based Light Sources)

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