RESUMO
We demonstrate vertical integration of nitride-based blue/green micro-light-emitting diodes (µLEDs) stacks with independent junctions control using hybrid tunnel junction (TJ). The hybrid TJ was gown by metal organic chemical vapor deposition (p + GaN) and molecular-beam epitaxy (n + GaN). Uniform blue, green and blue/green emission can be generated from different junction diodes. The peak external quantum efficiency (EQE) of the TJ blue µLEDs and green µLEDs with indium tin oxide contact is 30% and 12%, respectively. The carrier transportation between different junction diodes was discussed. This work suggests a promising approach for vertical µLEDs integration to enhance the output power of single LEDs chip and monolithic µLEDs with different emission colors with independent junction control.
RESUMO
In this work, we present fully transparent metal organic chemical vapor deposition (MOCVD)-grown InGaN cascaded micro-light-emitting diodes (µLEDs) with independent junction control. The cascaded µLEDs consisted of a blue emitting diode, a tunnel junction (TJ), a green emitting diode, and a TJ, without using any conductive oxide layer. We can control the injection of carriers into blue, green, and blue/green junctions in the same device independently, which show high optical and electrical performance. The forward voltage (Vf) at 20 A/cm2 for the TJ blue µLEDs and TJ green µLEDs is 4.06 and 3.13 V, respectively. These results demonstrate the efficient TJs and fully activated p-type GaN in the cascaded µLEDs. Such demonstration shows the important application of TJs for the integration of µLEDs with multiple color emissions.
RESUMO
High performance InGaN micro-size light-emitting diodes (µLEDs) with epitaxial tunnel junctions (TJs) were successfully demonstrated using selective area growth (SAG) by metalorganic chemical vapor deposition (MOCVD). Patterned n + GaN/n-GaN layers with small holes were grown on top of standard InGaN blue LEDs to form TJs using SAG. TJ µLEDs with squared mesa ranging from 10×10 to 100×100 µm2 were fabricated. The forward voltage (Vf) in the reference TJ µLEDs without SAG is very high and decreases linearly from 4.6 to 3.7 V at 20 A/cm2 with reduction in area from 10000 to 100 µm2, which is caused by the lateral out diffusion of hydrogen through sidewall. By contrast, the Vf at 20 A/cm2 in the TJ µLEDs utilizing SAG is significantly reduced to be 3.24 to 3.31 V. Moreover, the Vf in the SAG TJ µLEDs is independent on sizes, suggesting that the hydrogen is effectively removed through the holes on top of the p-GaN surface by SAG. The output power of SAG TJ µLEDs is â¼10% higher than the common µLEDs with indium tin oxide (ITO) contact.