Published in Physical Review Lettersby the American Physical Society, a recent study from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) at the Chinese Academy of Sciences (CAS) demonstrated how nitrogen vacancies (V_N) can resolve asymmetric carrier injection in GaN-based light-emitting diodes (LEDs), offering a practical solution to enhance device efficiency.

The team investigated the persistent challenge of asymmetric carrier relaxation in GaN/AlN quantum wells (QWs), where electrons cool significantly slower than holes, leading to energy loss and reduced LED performance. Using first-principles calculations and nonadiabatic molecular dynamics simulations, they 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—comparable to holes (relaxation time=0.12ps). The defect states also strengthened electron-phonon coupling, further accelerating carrier cooling.

The 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 like  exhibited continuous band structures and strong nonadiabatic coupling, enabling ultrafast electron relaxation. In contrast, defects outside  trapped electrons without improving cooling. The study ruled out extrinsic dopants like silicon, as their energy levels failed to align with the required states.

This work provides a blueprint for optimizing GaN-based optoelectronics by strategically engineering defects. By mitigating carrier imbalance, the approach could improve the efficiency of ultraviolet LEDs, which currently suffer from sub-10% quantum efficiency. The findings also highlight the dual role of defects—traditionally seen as detrimental—as tools for controlling semiconductor properties.