Insufficient hole injection is a major impediment to the luminescence efficiency of III-nitride light-emitting diodes (LEDs). In our previous work by Zhang et al. [Appl. Phys. Lett. 97, 062103 (2010)], high-density mobile three-dimensional hole gas is obtained in Mg-doped Al composition graded AlGaN layer with Al composition linearly decreasing from a certain value to 0. In this paper, it is revealed by a theoretical study that the hole injection efficiency in blue-light GaN-based LEDs can be greatly enhanced by using this polarization-doped method. An increase in the electroluminescence intensity and the internal quantum efficiency in polarization-doped GaN-based LEDs is observed, in comparison with a conventional LED.
Our simulated results [Appl. Phys. Lett. 98, 101110 (2011)] reveal that polarization-doped light-emitting diodes (LEDs) have improved internal quantum efficiency due to the enhanced hole injection caused by the improved hole concentration and smooth valence band. In this letter, in order to verify these calculated results, polarization-doped LEDs grown by metalorganic chemical vapor deposition are investigated. The results show that the polarization-doped LED has the improved electroluminescence intensity and external quantum efficiency (EQE) compared with the conventional LED. The influence of the degree of AlGaN gradation on polarization-doped LEDs is also studied. It is found that the polarization-doped LED has the highest EQE when the Al composition of the graded AlGaN is linearly decreased from 0.2 to 0.
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