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Nanoscale Res Lett ; 14(1): 268, 2019 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-31388778


In this report, we locally modulate the doping type in the n-AlGaN layer by proposing n-AlGaN/p-AlGaN/n-AlGaN (NPN-AlGaN)-structured current spreading layer for AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). After inserting a thin p-AlGaN layer into the n-AlGaN electron supplier layer, a conduction band barrier can be generated in the n-type electron supplier layer, which enables the modulation of the lateral current distribution in the p-type hole supplier layer for DUV LEDs. Additionally, according to our studies, the Mg doping concentration, the thickness, the AlN composition for the p-AlGaN insertion layer and the NPN-AlGaN junction number are found to have a great influence on the current spreading effect. A properly designed NPN-AlGaN current spreading layer can improve the optical output power, external quantum efficiency (EQE), and the wall-plug efficiency (WPE) for DUV LEDs.

Opt Express ; 27(12): A620-A628, 2019 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-31252842


For the [0001] oriented AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs), the holes in the p-type electron blocking layer (p-EBL) are depleted due to the polarization induced positive sheet charges at the last quantum barrier (LQB)/p-EBL interface. The hole depletion effect significantly reduces the hole injection capability across the p-EBL. In this work, we propose inserting a thin AlN layer between the LQB and the p-EBL, which can generate the hole accumulation at the AlN/p-EBL interface. Meanwhile, the holes can obtain the energy when traveling from the p-EBL into the multiple quantum wells (MQWs) by intraband tunneling through the thin AlN layer. As a result, the hole injection and the external quantum efficiency (EQE) have been remarkably enhanced. Moreover, we point out that the thick AlN insertion layer can further generate the hole accumulation in the p-EBL and increase the hole energy which helps to increase the hole injection. We also prove that the intraband tunneling for holes across the thick AlN insertion layer is facilitated by using the optimized structure.

Opt Express ; 27(12): A643-A653, 2019 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-31252844


In this work, the size-dependent effect for InGaN/GaN-based blue micro-light emitting diodes (µLEDs) 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 µLEDs, 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 µLEDs. 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.

Nanoscale Res Lett ; 13(1): 355, 2018 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-30411256


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.