Bottom tunnel junction-based blue LED with a thin Ge-doped current spreading layer

Abstract

In this work, we present a GaN-based blue LED construction utilizing bottom tunnel junction (TJ) grown by plasma-assisted molecular beam epitaxy. The setup allows for N-polar-like built-in field alignment while being grown on a Ga-polar substrate. In this study, we present an efficient bottom TJ LED in which the distance between the quantum well and device surface is only 25 nm. This is achieved by the utilization of an n-type current spreading layer consisting of 20 nm thick In0.02Ga0.98N with a Ge doping concentration of 7 × 1019 cm−3. Heavily Ge and Mg doped bottom TJs allowed achieving a low LED turn-on voltage of 2.75 V at 20 A/cm2 and a differential resistivity of 4.7 × 10−4 Ω cm2 at 1 kA/cm2. The device maintained high crystal quality and smooth morphology, which allows for its use as a light emitting platform for further integration. Although the p-up reference LED exhibits lower resistivity at high current, its luminous efficiency is lower than for bottom TJ LEDs.