Novel tunable phosphor-free white III-nitride light emitting diodes based on indium rich InGaN nanostructures

Abstract

Phosphor free tunable white light emitting diodes (LEDs) have been fabricated using stacked InGaN/GaN quantum wells (QWs) comprised of a lower set of red emitting QWs with an upper set of blue and green emitting QW layers. With antisurfactant treatment, indium rich InGaN nanostructures are incorporated in the InGaN/GaN quantum well during growth. AFM study shows the formation of InGaN nanostructures with an average diameter of 40-80 nm in the quantum well layer. This growth technique enables red emitting III-Nitride based LEDs to be generated. With the growth of additional stacked blue/green QWs on these red emitting QWs with InGaN nanostructure incorporation for white light generation, competition arises between the quantum well layers for thermalization of injected carriers. The transport of holes from the p-GaN layer determines the radiative recombination event as holes have a lower mobility than electrons. At low injection current, emission from the upper blue/green QWs layer dominates where electron-hole (e-h) pair recombination takes place. With higher injection current, more holes diffuse across the GaN barrier to recombine with electrons at the InGaN nanostructures in the lower sets of QWs. Based on the band structure for the stacked QWs, the existence of these In-rich nanostructures leads to more effective carrier trapping at the lower set of QWs as electrons have to overcome an additional potential barrier (at the interface of InGaN nanostructures to the InGaN well layer). There is also a higher tendency for thermalization of carriers at the lower energy states. The effect of band filling under higher injection current also enables the excess holes to recombine at the lower set of QW layers with indium rich nanostructure, which accounts for the continuous increase in higher emission wavelength from the EL spectra. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.