Jordan Smith Graduate Student Researcher, DenBaars Group
University of California, Santa Barbara
Emerging Challenges and Considerations When Characterizing μLEDs
Soon after the initial development of III-Nitride blue LEDs, researchers quickly developed and standardized characterization methods to better understand and improve device performance. Research concentrated on increasing light output and EQE (external quantum efficiency) of LED chips, often with diameters near 1 mm; today, focus is shifting to new applications such as μLED (microLED) display technology, where LED sizes are reduced to the order of 1 μm.
Characterizing μLEDs requires developing new standards, tools, and methods to properly characterize the devices. This is partly due to differences in application from solid-state lighting (SSL). Whereas LEDs for SSL are traditionally packaged (to maximize total output) and measured in integrating spheres, μLEDs should be measured “on-chip” to mimic their real-world usage. “On-chip” measurements introduce new variables and sources of error which must be considered (such as the collection angle). Additionally, reducing sizes of μLEDs causes proportionate decreases in test parameters (including driving current and output power) which necessitate more sensitive instrumentation and careful calibrations. In order meet these requirements while accommodating the many possible μLED device variations (of different wavelengths, substrates, sizes etc) being researched, it was necessary to construct a test station from the ground up.