Lu Hongxi

Reduction of Efficiency Droop and Modification of Polarization Fields of InGaN-Based Green Light-Emitting Diodes via Mg-Doping in the Barriers

We demonstrate that the Mg-doping in barriers can partially screen the polarization fields of InGaN-based green light-emitting diodes. The photocurrent spectra show that the Mg-doping samples have smaller polarization fields and the blue shift of the peak with increasing current is observed. The reduction of polarization fields can be attributed to the screening of the impurity holes generated by the Mg atoms in the barriers. The efficiency droop is sensitive to the Mg-doping concentration in barriers, while the sample with Mg concentration of 5 × 1019 cm−3 exhibits the lowest efficiency degradation of 12.4% at a high injection current.

Evaluation of light extraction efficiency for the light-emitting diodes based on the transfer matrix formalism and ray-tracing method*

The internal quantum efficiency (IQE) of the light-emitting diodes can be calculated by the ratio of the external quantum efficiency (EQE) and the light extraction efficiency (LEE). The EQE can be measured experimentally, but the LEE is difficult to calculate due to the complicated LED structures. In this work, a model was established to calculate the LEE by combining the transfer matrix formalism and an in-plane ray tracing method. With the calculated LEE, the IQE was determined and made a good agreement with that obtained by the ABC model and temperature-dependent photoluminescence method. The proposed method makes the determination of the IQE more practical and conventional.

Influence of growth conditions on the V-defects in InGaN/GaN MQWs

The influence of the growth temperature, TMIn/TEGa and V/III ratio on the V-defects of InGaN/GaN multi-quantum wells (MQWs) has been investigated and discussed. When the TMIn flow increases from 180 to 200 sccm, the density of V-defects increases from 2.72 × 1018 to 5.24 × 1018 cm−2, and the V-defect width and depth increase too. The density also increases with the growth temperature. The densities are 2.05 × 108, 2.72 × 1018 and 4.23 × 108 cm−2, corresponding to a growth temperature of 748, 753 and 758 °C respectively. When the NH3 flows are 5000, 6600 and 8000 sccm, the densities of the V-defects of these samples are 6.34 × 1018, 2.72 × 1018 and 4.13 × 1018 cm−2, respectively. A proper V/III ratio is needed to achieve step flow growth mode. We get the best quality of InGaN/GaN MQWs at a growth temperature of 753 °C TMIn flow at 180 sccm, NH3 flow at 6600 sccm, a flatter surface and less V-defects density. The depths of these V-defects are from 10 to 30 nm, and the widths are from 100 to 200 nm. In order to suppress the influence of V-defects on reverse current and electro-static discharge of LEDs, it is essential to grow thicker p-GaN to fill the V-defects.