Degradation of (In)AlGaN-Based UVB LEDs and Migration of Hydrogen

We report on the degradation of the electro-optical parameters of (In)AlGaN-based ultraviolet-B light-emitting diodes (LEDs) stressed at a constant dc current of 100 mA and the simultaneous change in the depth profile of the hydrogen (H) concentration during operation. The optical power of the LEDs decreased to ~45% of its initial value after 10 h of operation and saturated for longer operation times. In addition, the drive voltage dropped in about the first 10 h of operation and gradually increased in the following operation time. The possible changes in the impurity distribution in the LEDs during operation have been studied by means of secondary-ion-mass spectrometry of the magnesium (Mg) and the H depth profiles after 10 and 100 h of operation. We could not resolve any significant change in the Mg profile. In contrast, after 10 h of operation, the H concentration in the electron-blocking layer (EBL), p-side, and active region significantly reduced, and the H formed two concentration peaks close to the active region and deeper in the n-side. After 100 h, the H concentration in the EBL and p-side did not change, but the H in the n-side propagated further away from the pn junction. A degradation mechanism is proposed, which includes the breaking of atomic bonds of the H-containing defect complexes and the migration of H atoms during operation.