Fabrication and photoluminescence of strong phase-separated InGaN based nanopillar LEDs

A strong phase-separated InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) producing a blue-green dual-wavelength spectrum has been grown, and fabricated into two nanopillar array structures with different etching depths: one fabricated only on the p-GaN layer and the other penetrating through the active layers. Micro-photoluminescence (μ-PL) spectra have shown that compared with the as-grown (planar) LED, light extraction efficiency (LEE) is improved for both the shorter and the longer nanopillar array structures due to the increased light-extracting surface area and light-guiding effect, in contrast, internal quantum efficiency (IQE) is improved for only the longer one due to the relaxation of strain in the MQWs embedded in the nanopillars. Furthermore, the strain relaxation-induced peak blue-shift value is smaller for the green emission from In-rich quantum dots (QDs) than the blue emission from the InGaN matrix, and decreases for both the emissions with increasing temperature. The former is attributed to the quantum-confined Stark effect (QCSE) in the strong localized QDs of small size being smaller than in the InGaN matrix, the latter is due to the decrease of the thermal-mismatch strain in the MQWs with increasing temperature.