Limitation of simple np-n tunnel junction based LEDs grown by MOVPE

Abstract

We show evidence that tunnel junctions (TJs) in GaN grown by metal-organic vapor phase epitaxy are dominated by trap-assisted (Poole-Frenkel) tunneling. This stems from observations of the careful optimized doping for the TJs. Especially the p${}^{++}$ and the n${}^{++}$ layers are far from ideal. The n${}^{++}$ layer induces 3D growth, which can be seen by a rising oxygen signal in Secondary Ions Mass Spectroscopy (SIMS). Furthermore, Mg segregation observed by SIMS indicates a depletion region of more than 10 nm. Still, we could realize TJ based LEDs with a low penalty voltage of 1.1 V and a specific differential resistance of about 10${}^{-2}$ $\Omega$.cm${}^2$ at 20 mA without using an InGaN interlayer.