Wafer-Level Electroluminescence Metrology for InGaN Light-Emitting Diodes

We present a reliable and fast characterization system that measures the electroluminescence (EL) of light-emitting diodes (LEDs) at the epi-wafer level. This "EL Q-check system" requires simple pre-processes for the measurement, circumventing the full chip-fabrication processes. The developed EL Q-check system consists of three parts: a CO2 laser for p-GaN ablation, a diamond knife for delineating the measurement area on the wafer and isolating the damaged area during the CO2 laser ablation, and the actual EL measurement on the wafer. The accuracy and the usefulness of the EL Q-check system are experimentally tested with eleven LED wafers of different crystal qualities by comparing the EL performances from the proposed system with those of the fully fabricated LED chips. For this purpose, the same wafers were divided in half and test patterns and LED chips were processed, respectively. A surprisingly good correlation between the results obtained by two methods indicates that the developed EL Q-check system can be used for accurate, reliable, and fast epi-wafer evaluation.