Effect of n-GaN thickness on internal quantum efficiency in InxGa1-xN multiple-quantum-well light emitting diodes grown on Si (111) substrate

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The mechanism of the effect of n-GaN thickness on the internal quantum efficiency (IQE) in InxGa1-xN multiple-quantum-wells (MQWs) grown on GaN/Si by means of metal organic chemical vapor deposition has been investigated by x-ray diffractometry, photoluminescence, and transmission electron microscopy. It is found that the increasing n-GaN thickness obviously improves the IQE in InxGa1-xN MQWs. It is clarified that the threading dislocation density (TDD) directly determines the V-defect density and the V-defect density is lower than the TDD. As the n-GaN thickness increases from 1.0 to 2.0 μm, the TDD significantly decreases by one order of magnitude. The V-defect density obviously reduces from 3.9 × 109 cm−2 to 8.7 × 108 cm−2, while the IQE in InxGa1-xN MQWs is improved from 28.3 to 44.6%. As the GaN thickness increases, the V-defect density in the InxGa1-xN MQW decreases due to the reduction of TDD in GaN, and subsequently the nonradiative recombination centers are effectively eliminated due to the reduction of the V-defect density in the InxGa1-xN MQWs.