A study of InGaN/GaN multiple layer quantum dot (QD) structures with varying barrier thicknesses is reported. With increasing barrier thickness both a redshift in the photoluminescence (PL) peak energy and increase in the PL decay lifetime is observed. This is attributed to an increase in the size of the internal electric field and the influence on the electronic structure via the quantum confined Stark effect. Theoretical surface integral potential calculations support this interpretation. A minimum barrier thickness of 4 nm appears to be required for the formation of separate homogeneous QD layers.
A study of InGaN quantum dots (QDs) grown on two different GaN templates—GaN growth using a conventional two-step approach and growth using our recently developed high temperature (HT) AlN as a buffer—is reported. The HT AlN buffer leads to a significant reduction in the dislocation density, particularly screw dislocations, in subsequently deposited GaN. This reduction is confirmed by a significant decrease in the (0002) x-ray diffraction rocking curve width. The GaN on the HT AlN buffer leads to a high density (1010/cm2) of InGaN QDs, whereas in contrast InGaN QDs on the conventional GaN layer grown using the two-step approach have a much smaller density (∼108/cm2). Furthermore, the carrier lifetimes for the QDs on the GaN/HT AlN have been found to be up to nine times longer than those for the QDs on the conventional GaN.
An optical and structural study of InGaN/GaN quantum dots (QDs) is reported. With increasing InGaN deposition time, the dominant emission changes from wetting layer (WL) to QDs, and a strong redshift of the emission occurs. Emission from localized WL states is observed, with a density and nature very different to that due to the QDs. Structural measurements reveal a disordered WL, consistent with the form of the WL photoluminescence excitation spectra.
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