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. 2018 Nov 8;13(1):355.
doi: 10.1186/s11671-018-2776-y.

On the p-AlGaN/n-AlGaN/p-AlGaN Current Spreading Layer for AlGaN-based Deep Ultraviolet Light-Emitting Diodes

Jiamang Che  1   2 , Chunshuang Chu  1   2 , Kangkai Tian  1   2 , Jianquan Kou  1   2 , Hua Shao  1   2 , Yonghui Zhang  1   2 , Wengang Bi  1   2 , Zi-Hui Zhang  3   4
Affiliations

On the p-AlGaN/n-AlGaN/p-AlGaN Current Spreading Layer for AlGaN-based Deep Ultraviolet Light-Emitting Diodes

Jiamang Che et al. Nanoscale Res Lett. .

Abstract

In this report, AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with different p-AlGaN/n-AlGaN/p-AlGaN (PNP-AlGaN) structured current spreading layers have been described and investigated. According to our results, the adopted PNP-AlGaN structure can induce an energy barrier in the hole injection layer that can modulate the lateral current distribution. We also find that the current spreading effect can be strongly affected by the thickness, the doping concentration, the PNP loop, and the AlN composition for the inserted n-AlGaN layer. Therefore, if the PNP-AlGaN structure is properly designed, the forward voltage, the external quantum efficiency, the optical power, and the wall-plug efficiency for the proposed DUV LEDs can be significantly improved as compared with the conventional DUV LED without the PNP-AlGaN structure.

Keywords: Current spreading; DUV LED; External quantum efficiency; Valence band barrier height; Wall-plug efficiency.

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Not applicable.

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The authors declare that they have no competing interests.

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Figures

Fig. 1
Fig. 1
a Schematic diagrams for the studied devices (reference LED A and PNPNP-AlGaN LED), b schematic diagrams for the PNP-AlGaN structure with two PNP-AlGaN junctions, c schematic valence band diagram for the PNP-AlGaN structure with multiple PNP-AlGaN junctions, in which φ1, φ2, and φn denote the barrier height for each PNP-AlGaN junction along the [0001] orientation and n represents the PNP-AlGaN junction number
Fig. 2
Fig. 2
a Equivalent circuit of DUV LEDs with lateral current-injection scheme (J1 > J2 > J3 > J4 > …… > Jn) and b simplified equivalent circuit of the LED with PNP-AlGaN structure, the current paths (J1 and J2) are also shown
Fig. 3
Fig. 3
a Energy band diagram for LED B at the current density of 170 A/cm2. Ec, Ev, Efe, and Efh denote the conduction band, the valance band, and quasi-Fermi levels for electrons and holes, respectively, b lateral hole distribution in the last quantum well for LEDs A and B at the current density of 170 A/cm2, respectively
Fig. 4
Fig. 4
a Hole concentration profiles and b radiative recombination rate in the MQW region for LEDs A and B at the current density of 170 A/cm2, respectively
Fig. 5
Fig. 5
a Optical output power density and EQE as a function of the injection current, b current-voltage characteristic, c WPE in terms of the injection current for LEDs A and B, respectively
Fig. 6
Fig. 6
a Lateral hole distribution in the last quantum well, b hole concentration profiles and c radiative recombination rate profiles in the MQW region for LEDs A, T1, T2, T3, T4, and T5 at the current density of 170 A/cm2. The plotted curves for panels b and c are purposely shifted by 2 nm for better resolution
Fig. 7
Fig. 7
a Optical output power density, b current-voltage characteristics for LEDs A, T1, T2, T3, T4, and T5. Inset figure shows the zoom-in current-voltage curves
Fig. 8
Fig. 8
WPE as a function of the injection current for LEDs A, T1, T2, T3, T4, and T5. Inset figure shows the WPE and EQE for the studied LEDs with various thicknesses of the n-Al0.40Ga0.60N layer for the PNP-AlGaN junction at the current density of 170 A/cm2
Fig. 9
Fig. 9
a Lateral hole distribution in the last quantum well, b hole concentration profiles, and c radiative recombination rate profiles in the MQW region or LEDs A, D1, D2, D3, D4, and D5 at the current density of 170 A/cm2. The plotted curves for panels b and c are purposely shifted by 2 nm for better resolution
Fig. 10
Fig. 10
a Optical output power density and EQE as a function of the injection current, b current-voltage characteristics for LEDs A, D1, D2, D3, D4, and D5. Inset figure shows the zoom-in current-voltage curves
Fig. 11
Fig. 11
WPE as a function of the injection current for LEDs A, D1, D2, D3, D4, and D5. Inset figure shows the WPE and EQE for the studied LEDs with various doping concentrations of the n-Al0.40Ga0.60N layer at the current density of 170 A/cm2
Fig. 12
Fig. 12
a Lateral hole distribution in the last quantum well, b hole concentration profiles, and c radiative recombination rate profiles in the MQW region for LEDs A, N1, N2, N3, and N4 at the current density of 170 A/cm2. The plotted curves for panels b and c are purposely shifted by 2 nm for better resolution
Fig. 13
Fig. 13
a Optical output power density and EQE as a function of the injection current, b current-voltage characteristic for LEDs A, N1, N2, N3, and N4. Inset figure shows the zoom-in current-voltage curves
Fig. 14
Fig. 14
WPE as a function of the injection current for LEDs A, N1, N2, N3, and N4. Inset figure shows the WPE and EQE for LEDs with various number of PNP-AlGaN junction at the current density of 170 A/cm2
Fig. 15
Fig. 15
a Lateral hole distribution in the last quantum well, b hole concentration profiles, and c radiative recombination rate profiles in the MQW region for LEDs A, C1, C2, C3, C4, and C5 at the current density of 170 A/cm2. The plotted curves for panels b and c are purposely shifted by 2 nm for better resolution
Fig. 16
Fig. 16
a Optical output power density and EQE as a function of the injection current and b current-voltage characteristics for LEDs A, C1, C2, C3, C4, and C5
Fig. 17
Fig. 17
WPE as a function of the injection current for LEDs A, C1, C2, C3, C4, and C5. Inset figure shows the WPE and the EQE for the studied LEDs with various AlN compositions for the n-AlGaN layer at the current density of 170 A/cm2
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