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Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells

Hongping Zhao, Guangyu Liu, Jing Zhang, Jonathan D. Poplawsky, Volkmar Dierolf, and Nelson Tansu

Open Access Open Access

Abstract

Optimization of internal quantum efficiency (IQE) for InGaN quantum wells (QWs) light-emitting diodes (LEDs) is investigated. Staggered InGaN QWs with large electron-hole wavefunction overlap and improved radiative recombination rate are investigated for nitride LEDs application. The effect of interface abruptness in staggered InGaN QWs on radiative recombination rate is studied. Studies show that the less interface abruptness between the InGaN sub-layers will not affect the performance of the staggered InGaN QWs detrimentally. The growths of linearly-shaped staggered InGaN QWs by employing graded growth temperature grading are presented. The effect of current injection efficiency on IQE of InGaN QWs LEDs and other approaches to reduce dislocation in InGaN QWs LEDs are also discussed. The optimization of both radiative efficiency and current injection efficiency in InGaN QWs LEDs are required for achieving high IQE devices emitting in the green spectral regime and longer.

©2011 Optical Society of America

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Figures (15)
Fig. 1
Fig. 1 The concept of novel InGaN QWs / QDs structures with improved electron-hole wavefunction overlap.

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Fig. 2
Fig. 2 Schematics of the (a) conventional InzGa1-zN-GaN QW; (b) two-layer staggered InxGa1-xN / InyGa1-yN QW; and (c) three-layer staggered InyGa1-yN / InxGa1-xN / InyGa1-yN QW structures [47].

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Fig. 3
Fig. 3 The electroluminescence spectra for (a) conventional InGaN QW and (b) three-layer staggered InGaN QW LEDs emitting with peak wavelengths at 520-525 nm, as function of injection current levels.

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Fig. 4
Fig. 4 Light output power vs current density for conventional InGaN QW and three-layer staggered InGaN QW LEDs at λ~520–525 nm, with the band lineups schematic of three-layer staggered InGaN QW [48].

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Fig. 5
Fig. 5 Time resolved measurements on both 3-layer staggered InGaN QW and conventional InGaN QW LED samples, with peak emission wavelength at 520-525 nm. The measurements were carried out by employing 430-nm excitation lasers with pulse duration of 25 ps [48].

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Fig. 6
Fig. 6 Total carrier lifetime as a function of carrier density for conventional InGaN QW and staggered InGaN QW at monomolecular coefficient A = 1.6x107 s−1 and Auger coefficient C = 5x10−33 cm6s−1.

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Fig. 7
Fig. 7 Energy band lineups and electron, hole wavefunction for staggered InGaN QWs with (a) 0-Å interface In-content linear-grading; (b) 6-Å interface In-content linear-grading.

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Fig. 8
Fig. 8 Rsp spectra for staggered InGaN QWs with less abrupt interface by In-content linear-grading.

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Fig. 9
Fig. 9 Schematics of the growth temperature, TMIn-flow rate, and In-content for the LS-1 staggered InGaN QW [Fig. 9(a)] and the corresponding real growth temperature profiles [Fig. 9(b)].

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Fig. 11
Fig. 11 Schematics of the growth temperature, TMIn-flow rate, and In-content for the LS-3 staggered InGaN QW [Fig. 11(a)] and the corresponding real growth temperature profiles [Fig. 11(b)].

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Fig. 10
Fig. 10 Schematics of the growth temperature, TMIn-flow rate, and In-content for the LS-2 staggered InGaN QW [Fig. 10(a)] and the corresponding real growth temperature profiles [Fig. 10(b)].

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Fig. 12
Fig. 12 (a) CL spectra of conventional, LS-1 staggered, LS-2 staggered, and LS-3 staggered InGaN QWs emitting at 460-480nm with various CL excitation currents; (b) Integrated CL intensity of conventional, LS-1 staggered, LS-2 staggered, and LS-3 staggered InGaN QW versus CL excitation currents at T = 300K.

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Fig. 13
Fig. 13 Band lineups and electron and hole wavefunction for (a) conventional 30-Å InGaN QWs and (b) LS-3 staggered InGaN QW. (c) Schematic of the conduction band lineup without the polarization field for LS-3 staggered InGaN QW with GaN barriers, where the sub-layers at side contain 5-Å In0.18Ga0.82N, and the linearly-shaped 10-Å InxGa1-xN contain InGaN layers with In-content linearly modified from 0.18 to 0.4.

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Fig. 14
Fig. 14 (a) Spontaneous emission spectra for conventional InGaN QW and LS-3 staggered InGaN QW with carrier density from 1x1018 cm−3 up to 2x1019 cm−3; (b) spontaneous emission radiative recombination rate (Rsp) for conventional InGaN QW and LS-3 staggered InGaN QW at different carrier density upto 2x1019cm−3.

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Fig. 15
Fig. 15 (a) Schematic of the InGaN-GaN QW structure inserted with large bandgap barriers. (b) IQE (ηIQE ) as a function of total current density for 24-Å In0.28Ga0.72N / GaN QW, 24-Å In0.28Ga0.72N / 15-Å Al0.1Ga0.9N QW and 24-Å In0.28Ga0.72N / 15-Å Al0.83In0.17N QW.

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