Browsing by Author "Shao, Hua"

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Impact of the surface recombination on InGaN/GaN-based blue micro-light emitting diodes
(2019-06-10)
Kou, Jianquan
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Shen, Chih-Chiang
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Shao, Hua
;
Che, Jiamang
;
Hou, Xu
In this work, the size-dependent effect for InGaN/GaN-based blue micro-light emitting diodes (mu LEDs) is numerically investigated. Our results show that the external quantum efficiency (EQE) and the optical power density drop drastically as the device size decreases when sidewall defects are induced. The observations are owing to the higher surface-to-volume ratio for small mu LEDs, which makes the Shockley-Read-Hall (SRH) non-radiative recombination at the sidewall defects not negligible. The sidewall defects also severely affect the injection capability for electrons and holes, such that the electrons and holes are captured by sidewall defects for the SRH recombination. Thus, the poor carrier injection shall be deemed as a challenge for achieving high-brightness mu LEDs. Our studies also indicate that the sidewall defects form current leakage channels, and this is reflected by the current density-voltage characteristics. However, the improved current spreading effect can be obtained when the chip size decreases. The better current spreading effect takes account for the reduced forward voltage. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Increasing the hole energy by grading the alloy composition of the p-type electron blocking layer for very high-performance deep ultraviolet light-emitting diodes
(2019-04-01)
Zhang, Zi-Hui
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Kou, Jianquan
;
Chen, Sung-Wen Huang
;
Shao, Hua
;
Che, Jiamang
It is well known that the p-type AlGaN electron blocking layer (p-EBL) can block hole injection for deep ultraviolet light-emitting diodes (DUV LEDs). The polarization induced electric field in the p-EBL for [0001] oriented DUV LEDs makes the holes less mobile and thus further decreases the hole injection capability. Fortunately, enhanced hole injection is doable by making holes lose less energy, and this is enabled by a specifically designed p-EBL structure that has a graded MN composition. The proposed p-EEL can screen the polarization induced electric field in the p-EBL. As a result, holes will lose less energy after going through the proposed p-EBL, which correspondingly leads to the enhanced hole injection. Thus, an external quantum efficiency of 7.6% for the 275 nm DIN LED structure is obtained. (C) 2019 Chinese Laser Press
On the Carrier Transport for InGaN/GaN Core-Shell Nanorod Green Light-Emitting Diodes
(2019-01-01)
Kou, Jianquan
;
Chen, Sung-Wen Huang
;
Che, Jiamang
;
Shao, Hua
;
Chu, Chunshuang
In this paper, we model and investigate the carrier transport for the core-shell nanorod (NR) structured green light-emitting diodes (LEDs) for which the InGaN/GaN multiple quantum wells are grown on the nonpolar surface of the NR. Our results show the absence of polarization fields in the m-plane quantum wells for the core-shell NR LEDs, which manifest the flat energy band condition, the improved electron injection efficiency, and the high electron-hole wave functions overlap for the quantum wells, leading to the high radiative recombination rate and the enhanced quantum efficiency. We further find that the quantum efficiency is also affected by the vertical charge injection for the core-shell NR LEDs. The vertical charge injection is more sensitive to the doping concentration and the thickness of the p-GaN layer than of the n-GaN layer. Moreover, the increase of the NR height also leads to the nonuniform vertical charge injection.
On the Impact of Electron Leakage on the Efficiency Droop for AlGaN Based Deep Ultraviolet Light Emitting Diodes
(2020-06-01)
Chu, Chunshuang
;
Tian, Kangkai
;
Che, Jiamang
;
Shao, Hua
;
Kou, Jianquan
In this work, we have investigated the origin of efficiency droop for AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). We find that the efficiency droop is likely to be caused by the electron leakage for DUV LEDs studied in this work. The electron leakage arises from the unbalanced electron and hole injection efficiencies. The correlation between the efficiency droop and the electron leakage can be numerically calculated by manipulating the conduction band barrier height of the p-AlGaN electron blocking layer (p-EBL) for the proposed DUV LEDs. For the purpose of demonstrating that the efficiency droop for DUV LEDs can be experimentally decreased by reducing the electron leakage, a p(+)-GaN/In0.15Ga0.85N/n(+)-GaN tunnel junction on DUV LED is grown by using metal organic chemical vapor deposition (MOCVD) technology. The tunnel junction helps to enhance the hole injection, thus decreasing the electron leakage and the efficiency droop. Moreover, the parasitic emission in the p-type hole injection layer is no longer observed thanks to the decreased electron leakage level.