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KAUST Repository Item type Article Authors Ajia, Idris A.; Edwards, P. R.; Liu, Z.; Yan, J. C.; Martin, R. W.; Roqan, Iman S. Citation Excitonic localization in AlN-rich AlxGa1xN/AlyGa1yN multi-quantum-well grain boundaries 2014, 105 (12):122111 Applied Physics Letters

a -plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy Eloc and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL.

The authors have used metal organic chemical vapor deposition to grow InGaN∕GaN multiple quantum well (MQW) nanostripes on trapezoidally patterned c-plane sapphire substrates. Transmission electron microscopy (TEM) images clearly revealed that the MQWs grew not only on the top faces of the trapezoids but also on both lateral side facets along the [0001] direction defined by the selected area electron diffraction pattern. Meanwhile, dislocations that stretched from the interfaces between the GaN and the substrates did not pass through the MQWs in the TEM observation. Microphotoluminescence measurements verified that the luminescence efficiency from a single nanostripe was enhanced by up to fivefold relative to those of regular thin film MQW structures. Observation of the cathodoluminescence identified the areas of light emission and confirmed that enhanced emission occurred from the nanostripes.

We had investigated the potential of non‐polar a‐plane InGaN/GaN multiple quantum well (MQW) for high indium content blue/green emission. By comparisons of a‐plane and c‐plane MQW with different indium compositions, we concluded that without piezoelectric field, high indium content non‐polar a‐plane InGaN/GaN MQW is suitable for green light emitting diode (LED). Furthermore, similar to c‐plane GaN InGaN/GaN MQW, the localized state might enhance the performance of a‐plane MQW while the indium composition about 24% although the threading dislocation density (TDD) is quite high. On the other hand, the indium phase separation might also occur on a ‐plane InGaN/GaN MQW while the indium composition about 30% so that the photoluminescence intensity of the sample 810 °C low down and spectrum bandwidth broaden. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)