Efficiency and Forward Voltage of Blue and Green Lateral LEDs with V-shaped Defects and Random Alloy Fluctuation in Quantum Wells

For nitride-based blue and green light-emitting diodes (LEDs), the forward voltage Vfor is larger than expected, especially for green LEDs. This is mainly due to the large barriers to vertical carrier transport caused by the total polarization discontinuity at multiple quantum well and quantum barrier interfaces. The natural random alloy fluctuation in quantum wells has proven to be an important factor reducing Vfor. However, this does not suffice in the case of green LEDs because of their larger polarization-induced barrier. V-shaped defects (V-defects) have been proposed as another key factor in reducing Vfor to allow lateral injection into multiple quantum wells, thus bypassing the multiple energy barriers incurred by vertical transport. In this paper, to model carrier transport in the whole LED, we consider both random alloy and V-defect effects. A fully two-dimensional drift-diffusion charge-control solver is used to model both effects. The results indicate that the turn-on voltages for blue and green LEDs are both affected by random alloy fluctuations and the V-defect density. For green LEDs, Vfor decreases more due to V-defects, where the smaller polarization barrier at the V-defect sidewall is the major path for lateral carrier injection. Finally, we discuss how the V-defect density and size affects the results.

Automated summary

For nitride-based blue and green LEDs, the forward voltage is higher than expected, especially for green LEDs, due to polarization discontinuity at multiple quantum well and quantum barrier interfaces. V-shaped defects have been proposed as a key factor in reducing the forward voltage by enabling lateral carrier injection. In this study, the effects of random alloy fluctuations and V-defect density on carrier transport in the whole LED are modeled, revealing that V-defects significantly decrease the forward voltage for green LEDs.