On the Effect of Step-Doped Quantum Barriers in InGaN/GaN Light Emitting Diodes

Zhang, Zihui; Tan, Swee Tiam; Ju, Zhengang; Liu, Wei; Ji, Yun; Kyaw, Zabu; Dikme, Y.; Sun, Xiao Wei; Demir, Hilmi Volkan

doi:10.1109/jdt.2012.2204858

Cited by 52 publications

(54 citation statements)

References 45 publications

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“…[6][7][8]11 Moreover, for GaN/AlGaN/GaN heterostructure [refer to the inset of Fig. 6], the AlGaN layer is subject to the tensile strain, and thus, the piezoelectric field polarization and the spontaneous polarization are both oriented opposite to the growth orientation.…”

Section: -2 Zhang Et Almentioning

confidence: 99%

“…[1][2][3] The device performance is, however, still limited by Auger recombination, 4,5 charge separation, 6-9 current crowding, [10][11][12] insufficient hole injection, 9,[13][14][15][16][17][18] and electron overflow from the MQW active region. [19][20][21][22] In order to address these issues, a staggered quantum well architecture and also InGaN/GaN MQWs with Si-step-doped quantum barriers have been proposed to screen the quantum confined Stark effect (QCSE) and increase the spatial overlap of electron-hole wave functions, [7][8][9] while an improved current spreading can be obtained either by making the p-type layer more resistive or the p-contact layer more conductive. 10,11 Additionally, an improved crystal quality is also essential for improving the device efficiency.…”

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confidence: 99%

“…8 The simulation parameters regarding the Auger recombination coefficient, the Shockley-Read-Hall recombination lifetime and other nitrogen-contained simulation parameters can be found elsewhere, and specifically, considering the dislocation generation due to strain relaxation during the epitaxial growth, we have assumed a 40% polarization level. 8,10,11 The relationship among the captured electrons by quantum wells, mean free path and injected electrons can be expressed in Eqs. (1) and (2) …”

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On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer

Zhang

Liu

et al. 2014

Applied Physics Letters

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Cataloged from PDF version of article.In this work, the origin of electron blocking effect of n-type Al 0.25Ga0.75N electron blocking layer (EBL) for c+ InGaN/GaN light-emitting diodes has been investigated through dual-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron overflow from the active region and increases the radiative recombination rate with holes. © 2014 AIP Publishing LLC

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Section: -2 Zhang Et Almentioning

confidence: 99%

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confidence: 99%

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On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer

Zhang

Liu

et al. 2014

Applied Physics Letters

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“…12 Apart from the above methods, the polarization induced electric field within the quantum wells can be screened by Si doping the quantum barriers. 13 According to the report by Zhang et al, 13 in addition to the electrons released by those Si dopants in the quantum barriers, the ionized Si dopants are also essential in screening the polarization induced electric field within the quantum wells, and thus the QCSE. The drawback of a high Si doping level in the quantum barriers is that it will block the hole injection across the whole active region.…”

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confidence: 99%

“…The drawback of a high Si doping level in the quantum barriers is that it will block the hole injection across the whole active region. 13 Therefore, it will be useful to replace those ionized dopants with any other electrically charged particles which can avoid the hole blocking effect. Hence, in this work, we have proposed the In y Ga 1Ày N/ In x Ga 1Àx N quantum well/quantum barrier architecture, in which the InN composition x in the quantum barrier is graded along the growth direction, so that the polarization induced bulk charges are generated to replace the ionized dopants in the quantum barriers, and have an excellent screening effect on the polarization induced electric field in the quantum wells.…”

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Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers

Zhang

Liu

et al. 2014

Applied Physics Letters

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Cataloged from PDF version of article.InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices. (C) 2014 AIP Publishing LLC

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Correlative High‐Resolution Mapping of Strain and Charge Density in a Strained Piezoelectric Multilayer

Song

Koch

Lee

et al. 2014

Adv Materials Inter

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A key to strain engineering of piezoelectric semiconductor devices is the quantitative assessment of the strain‐charge relationship. This is particularly demanding in current InGaN/GaN‐based light‐emitting diode (LED) designs as piezoelectric effects are known to degrade the device performance. Using the state‐of‐the‐art inline electron holography, we have obtained fully quantitative maps of the two‐dimensional strain tensor and total charge density in conventional blue LEDs and correlated these with sub‐nanometer spatial resolution. We show that the In0.15Ga0.85N quantum wells are compressively strained and elongated along the polar growth direction, exerting compressive stress/strain on the GaN quantum barriers. Interface sheet charges arising from a polarization gradient are obtained directly from the strain data and compared with the total charge density map, quantitatively verifying only 60% of the polarization charges are screened by electrons, leaving a substantial piezoelectric field in each In0.15Ga0.85N quantum well. The demonstrated capability of inline electron holography provides a technical breakthrough for future strain engineering of piezoelectric optoelectronic devices.

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On the Effect of Step-Doped Quantum Barriers in InGaN/GaN Light Emitting Diodes

Cited by 52 publications

References 45 publications

On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer

On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers

Correlative High‐Resolution Mapping of Strain and Charge Density in a Strained Piezoelectric Multilayer

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