Effects of activation method and temperature to III-nitride micro-light-emitting diodes with tunnel junction contacts grown by metalorganic chemical vapor deposition

The optical and electrical characteristics of InGaN blue and green micro-light-emitting diodes (mu LEDs) with GaN tunnel junction (TJ) contacts grown by metalorganic chemical vapor deposition (MOCVD) were compared at different activation temperatures among three activation methods from the literature, namely, sidewall activation, selective area growth (SAG), and chemical treatment before sidewall activation. The devices with chemical treatment before activation resulted in uniform electroluminescence and higher light output power, compared to the devices with sidewall activation and SAG. Moreover, the green mu LEDs showed greater optical degradation at elevated activation temperatures, whereas the blue mu LEDs yielded trivial difference with activation temperatures from 670 to 790 & DEG;C. The 5 x 5 mu m(2) devices with chemical treatment before activation and SAG yielded almost identical voltage at 20 A/cm(2), and the voltage penalty significantly decreased with activation temperature in the case of devices with sidewall activation. The devices with chemical treatment before activation resulted in higher external quantum efficiency (EQE) and wall-plug efficiency (WPE) in low current density range compared to the devices with SAG. The enhancements in EQE and WPE were observed in different mu LED sizes, suggesting that chemical treatment before sidewall activation enables the use of TJ contacts grown by MOCVD and is advantageous for applications that require high brightness and efficiency.