Fabrication of high power InGaN/GaN multiple quantum well blue LEDs grown on patterned Si substrates

InGaN/GaN MQW LEDs were grown on patterned Si substrates with the insertion of high temperature AlNx nucleation layers, SiNx interlayers and AlGaN/AlN buffer layers. It was found that the SiNx interlayer could improve the GaN crystal quality by blocking some of the edge and mixing dislocations. AlGaN/AlN buffer layer could further decrease the residue tensile stress and increase crystal quality. Cross-sectional TEM images showed that the AlGaN buffer layer could terminate some of the dislocations at the interface of AlGaN and GaN. Without substrate removal and specific device packaging, the LEDs on Si emitted 1 mW output power at 20 mA injection current on average. The forward voltage of LED on Si was 4.32 V, which was larger than that on the sapphire, mainly because of the bad crystal quality of n-GaN on the Si substrates. Light emitting spatial distribution along the LEDs platforms on the patterned Si substrates were studied by CL measurements. CL images exhibited that longer wavelength light was emitted from the corner and the edge regions of LED platforms. Tof-SIMS mapping showed that this resulted from more In compositions at those regions. Temperature dependent EL, PL and CL measurements were performed to investigate the additional broad ~ 3.1 eV peak, D peak, and the anomalous temperature dependent EL characteristics of the InGaN/GaN LEDs. The possible physical interpretations were explained by the “QW hypothesis” and the “defect hypothesis”. New substrates transferring processes, adapted to the application of InGaN/GaN LEDs grown on Si, were developed and studied. Electroplated Cu was used as the new transferring substrates. The original Si substrates were totally removed by ICP dry etching. 500 μm x 500 μm LEDs on Cu were finally fabricated. The EL output power was 2.78 mW with 55 mA injection current at 5.4 V. It was 1.78 times larger than that of the top emitting LEDs on the Si. The output power could reach as high as 16 mW at 500 mA injection current. The wavelength of the LEDs on Cu was blue shift compared with the LED on the Si, resulting from the stress release