Electroluminescence efficiency of blue InGaN∕GaN quantum-well diodes with and without an n-InGaN electron reservoir layer

Otsuji, N.; Fujiwara, K.; Sheu, Jinn-Kong

doi:10.1063/1.2398690

Cited by 47 publications

(50 citation statements)

References 16 publications

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“…1(a), and comprised the following functional layers: a 2 lm thick undoped GaN buffer layer; a 2 lm thick n-type GaN layer; two In 0.10 Ga 0.90 N QWs of 3 nm thickness with 10 nm GaN barrier layers; six In 0.25 Ga 0.75 N QWs again of 3 nm thickness and separated by 10 nm GaN barriers; and finally a 240 nm Mgdoped GaN layer. The first two QWs function as an electron reservoir layer (ERL) for improving the carrier capture rate 22 and mitigating the efficiency droop by reducing the overflow of "hot electrons". 23 In the context of this study, their presence also gave an opportunity to compare the effect of strain relaxation on QWs of different alloy compositions.…”

Section: Methodsmentioning

confidence: 99%

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

Xie

Chen

Edwards

et al. 2012

Journal of Applied Physics

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This version is available at https://strathprints.strath.ac.uk/40400/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the A size-dependent strain relaxation and its effects on the optical properties of InGaN/GaN multiple quantum wells (QWs) in micro-pillars have been investigated through a combination of high spatial resolution cathodoluminescence (CL) hyperspectral imaging and numerical modeling. The pillars have diameters (d) ranging from 2 to 150 lm and were fabricated from a III-nitride light-emitting diode (LED) structure optimized for yellow-green emission at $560 nm. The CL mapping enables us to investigate strain relaxation in these pillars on a sub-micron scale and to confirm for the first time that a narrow ( 2 lm) edge blue-shift occurs even for the large InGaN/GaN pillars (d > 10 lm). The observed maximum blue-shift at the pillar edge exceeds 7 nm with respect to the pillar centre for the pillars with diameters in the 2-16 lm range. For the smallest pillar (d ¼ 2 lm), the total blue-shift at the edge is 17.5 nm including an 8.2 nm "global" blue-shift at the pillar centre in comparison with the unetched wafer. By using a finite element method with a boundary condition taking account of a strained GaN buffer layer which was neglected in previous simulation works, the strain distribution in the QWs of these pillars was simulated as a function of pillar diameter. The blue-shift in the QWs emission wavelength was then calculated from the strain-dependent changes in piezoelectric field, and the consequent modification of transition energy in the QWs. The simulation and experimental results agree well, confirming the necessity for considering the strained buffer layer in the strain simulation. These results provide not only significant insights into the mechanism of strain relaxation in these micro-pillars but also practical guidance for design of micro/nano LEDs.

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Section: Methodsmentioning

confidence: 99%

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

Xie

Chen

Edwards

et al. 2012

Journal of Applied Physics

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“…However, it should be noted that no direct experimental evidence for strain relaxation was found. Otsuji et al 10 and Takahashi et al 12 reported an increase in the electroluminescence (EL) intensity of a three-period In 0.3 Ga 0.7 N/GaN multiple QW device, over a range of temperatures, when including a 15 nm thick Si-doped In 0.18 Ga 0.82 N prelayer beneath the QW stack. The increase in intensity was ascribed, in both reports, to an enhancement of the electron capture efficiency, due to the prelayer behaving as an electron reservoir.…”

Section: Introductionmentioning

confidence: 99%

“…As the internal quantum efficiency (IQE) is determined by competition between radiative and non-radiative recombination processes, slower radiative recombination rates can limit the IQE. It has been reported [10][11][12][13][14][15][16][17][18][19] that the inclusion of an InGaN layer prior to the deposition of the 1st QW, a so-called "prelayer," can lead to significant improvements in the IQE of InGaN multiple QW structures and LEDs. Typical prelayer structures consist of 20-30 nm of intentionally Si-doped (In)GaN, which can be either a single layer or a short-period superlattice, positioned a few nanometers beneath the 1st QW.…”

Section: Introductionmentioning

confidence: 99%

A comparison of the optical properties of InGaN/GaN multiple quantum well structures grown with and without Si-doped InGaN prelayers

Davies

Hammersley

Massabuau

et al. 2016

Journal of Applied Physics

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In this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer. In photoluminescence and photoluminescence excitation spectroscopy, a 2nd emission band, occurring at a higher energy, was identified in the spectrum of the multiple quantum well structure containing the InGaN prelayer, originating from the first quantum well in the stack. Band structure calculations revealed that a reduction in the resultant electric field occurred in the quantum well immediately adjacent to the InGaN prelayer, therefore leading to a reduction in the strength of the quantum confined Stark effect in this quantum well. The partial suppression of the quantum confined Stark effect in this quantum well led to a modified (higher) emission energy and increased radiative recombination rate. Therefore, we ascribed the origin of the high energy emission band to recombination from the 1st quantum well in the structure. Study of the temperature dependent recombination dynamics of both samples showed that the decay time measured across the spectrum was strongly influenced by the 1st quantum well in the stack (in the sample containing the prelayer) leading to a shorter average room temperature lifetime in this sample. The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36% compared to 25%) which was thus attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with nonradiative recombination processes.

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“…External quantum efficiencies as high as 70% [1] occur in c-plane wurtzite (In)GaN despite the large built-in electric field across the QWs due to the discontinuities in the spontaneous polarisation at the interfaces between GaN and InGaN layers, and the piezoelectric polarisation due to the strain in the InGaN layers grown on GaN [2]. There have been several reports [3][4][5][6][7][8][9][10][11][12][13] that the growth of a layer of InGaN, 10s of nm thick and referred to as a prelayer, prior to the first QW in multiple QW (MQW) structures and LEDs leads to increases in the measured luminescence intensity and room temperature (RT) internal quantum efficiency (IQE). Suggestions for the mechanism by which prelayers bring about these improvements have included strain reduction in the QW layers [3], acting as an "electron reservoir" from which carriers tunnel into the QWs [4], and a reduction in the density of point defects in the active region [5,[8][9][10].…”

mentioning

confidence: 99%

“…There have been several reports [3][4][5][6][7][8][9][10][11][12][13] that the growth of a layer of InGaN, 10s of nm thick and referred to as a prelayer, prior to the first QW in multiple QW (MQW) structures and LEDs leads to increases in the measured luminescence intensity and room temperature (RT) internal quantum efficiency (IQE). Suggestions for the mechanism by which prelayers bring about these improvements have included strain reduction in the QW layers [3], acting as an "electron reservoir" from which carriers tunnel into the QWs [4], and a reduction in the density of point defects in the active region [5,[8][9][10]. We have previously demonstrated [11][12][13] that the QW IQE improvements associated with the inclusion of prelayers can be explained as being due to the modification of the surface polarisation field between the sample surface and the prelayer which opposes the fields across the QWs.…”

mentioning

confidence: 99%

Room temperature PL efficiency of InGaN/GaN quantum well structures with prelayers as a function of number of quantum wells

Christian

Hammersley

Davies

et al. 2016

Phys. Status Solidi C

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We report on the effects of varying the number of quantum wells (QWs) in an InGaN/GaN multiple QW (MQW) structure containing a 23 nm thick In0.05Ga0.95N prelayer doped with Si. The calculated conduction and valence bands for the structures show an increasing total electric field across the QWs with increasing number of QWs. This is due to the reduced strength of the surface polarisation field, which opposes the built‐in field across the QWs, as its range is increased over thicker samples. Low temperature photoluminescence (PL) measurements show a red shifted QW emission peak energy, which is attributed to the enhanced quantum confined Stark effect with increasing total field strength across the QWs. Low temperature PL time decay measurements and room temperature internal quantum efficiency (IQE) measurements show decreasing radiative recombination rates and decreasing IQE, respectively, with increasing number of QWs. These are attributed to the increased spatial separation of the electron and hole wavefunctions, consistent with the calculated band profiles. It is also shown that, for samples with fewer QWs, the reduction of the total field across the QWs makes the radiative recombination rate sufficiently fast that it is competitive with the efficiency losses associated with the thermal escape of carriers. (© 2016 The Authors. Phys. Status Solidi C published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Electroluminescence efficiency of blue InGaN∕GaN quantum-well diodes with and without an n-InGaN electron reservoir layer

Abstract: Articles you may be interested inEffect of an electron blocking layer on the piezoelectric field in InGaN/GaN multiple quantum well light-emitting diodes Appl.

Cited by 47 publications

References 16 publications

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

A comparison of the optical properties of InGaN/GaN multiple quantum well structures grown with and without Si-doped InGaN prelayers

Room temperature PL efficiency of InGaN/GaN quantum well structures with prelayers as a function of number of quantum wells

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