Harnessing III-Nitride Built-In Field in Multi-Quantum Well LEDs.

Abstract

III-nitrides possess several unique qualities, which allow them to make the world brighter, but their uniqueness is not always beneficial. The uniaxial nature of the wurtzite crystal leads to strikingly large electric polarization fields, which along with the high acceptor ionization energy cause low injection efficiency and uneven carrier distribution for multiple quantum well (QW) light emitting devices. In this work, we explore the carrier distribution in Ga-polar LED in two configurations: standard "p-up" and "p-down", which is accomplished by utilizing a bottom-tunnel junction. This enables the inversion of the sequence of the p and n layers while altering the direction of the current flow with respect to the inherent polarization. To probe the carrier distribution two, color-coded QWs are used in alternating sequences. Our study reveals that for "p-down" devices carrier transport through multiple QWs is limited by the potential barrier at the QW interface, which is in contrast to results for "p-up" structures, where hole mobility is the bottleneck. Moreover, investigated "p-down" LEDs exhibit an extremely low turn-on voltage.