Abstract
Non-polar (11–20) InGaN quantum dots (QDs) have been grown using a modified droplet epitaxy method by metal-organic vapour phase epitaxy on top of a 15-period AlN/GaN distributed Bragg reflector (DBR) on a-plane GaN pseudo-substrate prepared by epitaxial lateral overgrowth (ELOG), in which the QDs are located at the centre of a ca. 180 nm GaN layer. The AlN/GaN DBR has shown a peak reflectivity of ∼80% at a wavelength of ∼454 nm with a 49 nm wide, flat stop-band. Variations in layer thicknesses observed by cross-sectional scanning transmission electron microscopy have been identified as the main source of degradation of the DBR reflectivity. The presence of trenches due to incomplete coalescence of the ELOG template and the formation of cracks due to relaxation of tensile strain during the DBR growth may distort the DBR and further reduce the reflectivity. The DBR top surface is very smooth and does not have a detrimental effect on the subsequent growth of QDs. Enhanced single QD emission at 20 K was observed in cathodoluminescence.
Highlights
Nitride quantum dots (QDs) offer great potential to achieve single photon emission at room temperature [1], due to the large band offset between the quantum dot structure and the matrix and the large exciton binding energy [2]
We report on the growth of a 15-period AlN/GaN distributed Bragg reflector (DBR) on a-plane GaN template, prepared by epitaxial lateral overgrowth (ELOG) by metal-organic vapour phase epitxay (MOVPE)
All non-polar a-plane (11e20) samples were grown on r-plane sapphire by MOVPE in a Thomas Swan close-coupled showerhead reactor using tri-methyl indium (TMI), tri-methyl gallium (TMG), tri-methyl aluminium (TMA) and ammonia as precursors
Summary
Nitride quantum dots (QDs) offer great potential to achieve single photon emission at room temperature [1], due to the large band offset between the quantum dot structure and the matrix and the large exciton binding energy [2]. Growth of non-polar InGaN QDs with much shorter exciton recombination lifetimes [5] (an order of magnitude lower than the corresponding polar equivalent structures [6]) has recently been demonstrated. With the superior optical properties of non-polar InGaN QDs, high quality, high reflectivity DBRs are needed to enhance the spontaneous emission rate and light extraction efficiency for single photon source applications [15], and are relevant to more conventional non-polar GaN-based opto-electronic devices, such as resonant cavity light emitting diodes (RCLEDs) [16] and vertical cavity surface emitting lasers (VCSELs) [17,18]. We have observed enhanced QD emission based on this structure in CL at 20 K, suggesting the light extraction efficiency of single QD emission has been increased This marks an important step towards the development of devices based on non-polar InGaN QDs in microcavities
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