InGaN quantum dots (QDs) with a high density up to 9×1010/cm2 have been obtained on a surface of high quality GaN grown using high temperature AlN as a buffer layer on sapphire substrates. X-ray diffraction measurements indicate that the full width at half maximum of rocking curve of the GaN in (0002) direction has been reduced to as narrow as 61 arc sec. The growth of the InGaN QDs has been found to be different from the formation of other III–V semiconductor QDs in the conventional Stranski–Krastanov mode. Too high NH3 flow rate leads to the InGaN QDs in a large diameter up to 50 nm with a density of ∼1010/cm2, while too low NH3 flow rate results in disappearance of the InGaN QDs. The growth mechanism for the InGaN QDs due to the change in NH3 flow rate has been discussed. The optical properties of the InGaN QDs have been investigated. A stimulated emission from the InGaN multiple QD layers has been observed under an optical pumping with a low threshold at room temperature. The influence of thickness of the GaN barrier and growth temperature for the GaN barrier on InGaN QDs has been investigated, in combination with optical pumping measurements. Our results indicate that both the thickness of the GaN barrier and growth temperature for the GaN barrier should be carefully chosen. Otherwise, either the formation of the InGaN QDs can be prevented or the InGaN QDs that have been formed can be destroyed.
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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