The properties of reversed polarization yellow InGaN-GaN MQWs in p-side down structure grown by metal–organic chemical vapor deposition on sapphire substrate

• PDMQWs and NDMQWs were investigated and compared systematically.
• Rough p-GaN promotes the formation of In-rich nanodot-like structure in PDMQWs.
• PDMQWs present longer emission wavelength with an extra emission peak from nanodot-like structures.
• Mg memory effect cause Mg residual and the incorporation of C, H, and O impurities in PDMQWs.

The reversed polarization yellow emission InGaN/GaN multiple quantum wells (MQWs) in p-side down (PDMQWs) and n-side down (NDMQWs) structures were grown by metal–organic chemical vapor deposition on sapphire substrates. The properties of PDMQWs in surface morphology, interface quality, optical characteristic, and impurities distribution were investigated and compared with those of NDMQWs. Though degrading the interface abruptness of PDMQWs, the rough surface of p-GaN underlying layer was found to promote InGaN compositional fluctuation or phase separation and the resultant formation of nanodot-like structures with higher In-composition. At the same growth conditions and the similar In-composition for two MQWs, PDMQWs present a longer emission wavelength with an extra emission peak from In-rich nanodot-like structures, compared with that of NDMQWs. Mg memory effect introduces high concentrations of Mg residual in PDMQWs accompanying with the incorporation of C, H, and O impurities, which impose negative influence on the optical properties of PDMQWs. The potentials and problems, as well as the possible problem-solving methods of p-side down light-emitting diodes (PDLEDs) in developing long wavelength emitter were also discussed, which may bring some new thinkings for the design of III-nitrides PDLEDs.

shows the surface morphology of NDMQWs and PDMQWs. It clearly shows that the rough surface of p-GaN underlying layer can promote the formation of InGaN nanodot-like structure.