Investigation of sidewall damage induced by reactive ion etching on AlGaInP MESA for micro-LED application

Previous reports have studied the impact of sidewall defects on AlGaInP micro light emitting diode (mu LED) only by Current-Voltage-Luminescence (I-V-L) measurements. In this work, we propose an alternative approach to investigate these defects directly after MESA formation, by coupling optical characterization techniques together with Time-of-flight secondary ion mass spectrometry (TOF-SIMS) on A1GaInP square shaped pixels of different sizes formed by BCl3-based Reactive Ion Etching (RIE). It is found that for a 6 x 6 mu m(2) pixel, the light emission homogeneity is largely impacted by the sidewall defects. From emission efficiency map deduced by temperature-dependent cathodoluminescence measurements, we estimate that 84.5% of the 6 x 6 mu m(2) pixel exhibit a lower efficiency than the center. The carriers lifetime extracted from time-resolved photoluminescence (TRPL) measurements on larger pixel begins to decrease gradually at 3 mu m from the sidewall due to non-radiative recombinations. On the other hand, the TOF-SIMS analysis shows that residues of boron and chlorine remain on the surface and sidewalls of the pixel after BCl3 etching. These results show the importance to characterize the mu LEDs at the MESA step and the necessity to optimize the etching process and the passivation.