Luminescence mechanism and carrier dynamic studies of InGaN-based dichromatic light emitting diodes with ultraviolet and blue emissions

In this study, to investigate the luminescence mechanism and carrier dynamics of dichromatic InGaN-based light emitting diodes (LEDs) with two active regions, an ultraviolet (UV)–blue LED (UV active region above the blue one) and a blue–UV LED (blue active region above the UV one) were prepared. Photoluminescence (PL), cathodoluminescence (CL), and time-resolved photoluminescence measurements were performed. For the PL spectra of both LEDs, the blue emissions are stronger than the UV emissions. This trend shows that the higher degree of carrier localization of the blue active region, in either the upper or lower portions of the LEDs, can enhance carrier capture and recombination efficiency. Due to the large and bright light spots emitted from indium-rich clusters in the blue active region, CL images showed that the blue emission is dominant in the image shape for both samples. Furthermore, it was shown that the optical properties and carrier dynamics of dichromatic InGaN-based LEDs could be well explained by the combined effects of the carrier localization effect, structures, extraction efficiency, defect density, and carrier capture efficiency in the UV and blue active regions. Also, thermal effect plays an important role in carrier transport behavior in such dichromatic LEDs. The research results provide important information for operation mechanisms and device designs of dichromatic LEDs.