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Enhanced electroluminescence using Ta2O5/ZnO/HfO2 asymmetric double heterostructure in ZnO/GaN-based light emitting diodes

Hao Long, Songzhan Li, Xiaoming Mo, Haoning Wang, Zhao Chen, Zhe Chuan Feng, and Guojia Fang

Open Access Open Access

Abstract

ZnO/GaN-based light-emitting diodes (LEDs) with improved asymmetric double heterostructure of Ta2O5/ZnO/HfO2 have been fabricated. Electroluminescence (EL) performance has been enhanced by the HfO2 electron blocking layer and further improved by continuing inserting the Ta2O5 hole blocking layer. The origins of the emission have been identified, which indicated that the Ta2O5/ZnO/HfO2 asymmetric structure could more effectively confine carriers in the active i-ZnO layer and meanwhile suppresses of radiation from GaN. This device exhibits superior stability in long-time running. It’s hoped that the asymmetric double heterostructure may be helpful for the development of the future ZnO-based LEDs.

© 2014 Optical Society of America

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Figures (6)
Fig. 1
Fig. 1 The I-V characteristic of the LEDs in dark at RT. The insets show the schematic diagram of LED 3 with structure of n-ZnO/Ta2O5/i-ZnO/HfO2/p-GaN and the I-V curves of the In/p-GaN and the Ag/n-ZnO contacts, respectively.

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Fig. 2
Fig. 2 The left column shows the EL spectra of the LEDs under different injection currents. The right column shows the Gaussian fits of the EL spectra of LEDs under the same injection current of 2.00 mA.

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Fig. 3
Fig. 3 RT PL spectra of p-GaN and Ta2O5/i-ZnO/HfO2/p-GaN. Peak-deconvolution with Gaussian function is applied in the PL spectra. The inset shows RT transmission spectrum of p-GaN.

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Fig. 4
Fig. 4 (a) The plots of EL integrated intensity versus injection current of LEDs. (b) EL intensity of respective peaks versus various LEDs under the same injection current of 2.00 mA.

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Fig. 5
Fig. 5 The energy band structures for (a) LED 1, (b) LED 2 and (c) LED 3.

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Fig. 6
Fig. 6 (a) The emission intensity of the band at 633 nm of LED 3 as a function of the 24-hour driving time recorded every 120 second intermittently with a continuous injection current of 2.00 mA. The inset shows the result of long-time stability test recorded every 10 hour intermittently also with a continuous injection current of 2.00 mA. (b) The EL spectra of LED 3 before and after running 24 hours, and after stopping continuous work 2 hours.

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Tables (1)

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Table 1 ΔEC of ZnO/EBLs and ΔEV of EBLs/GaN of various materials

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