A study published in Physical Review Letters and conducted by researchers from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences demonstrated how nitrogen vacancies (V_N) resolve asymmetric carrier injection in GaN-based light-emitting diodes (LEDs), providing a practical way to improve device efficiency.

Researchers investigated the asymmetric carrier relaxation in GaN/AlN quantum wells (QWs), where electrons cool significantly slower than holes, leading to energy loss and reduced LED performance. 

Through first-principles calculations and nonadiabatic molecular dynamics simulations, researchers analyzed the role of V_N introduced at the GaN/AlN interface. These defects created intermediate states that acted as "steps" for electrons, reducing their relaxation time from 8.61 ps to 0.15 ps which is comparable to holes (0.12ps). The defect states strengthened electron-phonon coupling, further accelerating carrier cooling.

Moreover, researchers identified eight configurations of V_N, with four located in the critical energy interval (E_g2) between the conduction band minimum (CBM) and higher states. Systems exhibited continuous band structures and strong nonadiabatic coupling, enabling ultrafast electron relaxation. In contrast, defects outside trapped electrons without improving cooling. Extrinsic dopants like silicon were ruled out, as their energy levels failed to align with the required states.

The study provides a blueprint for optimizing GaN-based optoelectronics by strategically engineering defects. The approach could improve the efficiency of ultraviolet LEDs by mitigating carrier imbalance, which currently suffer from sub-10% quantum efficiency. Besides, this study highlights the role of defects as tools to control semiconductor properties.