Metalorganic chemical vapor deposition-grown tunnel junctions for low forward voltage InGaN light-emitting diodes: epitaxy optimization and light extraction simulation

In this work, we demonstrate the detailed optimization of metalorganic chemical vapor deposition (MOCVD)-grown tunnel junctions (TJs) utilizing selective area growth (SAG) for regular size (0.1 mm²) and micro-size InGaN light-emitting diodes (LEDs and µLEDs). Finite-difference time-domain simulations show that the SAG apertures result in a more directional light emission of far-field radiation pattern for the SAG TJ LEDs grown on patterned sapphire substrate. Moreover, it is noted that the n-InGaN insertion layer and Si-doped concentration in the n⁺GaN TJs layer is essential to realize a low forward voltage (V _f) in TJs LEDs. For both 0.1 mm² LEDs and µLEDs, the V _f is independent on the SAG aperture space varied from 3 to 8 µm when the Si-doping level in the n⁺GaN layer is as high as 1.7 × 10²⁰ cm⁻³. The optimized TJ LEDs exhibit a comparable differential resistance of 1.0 × 10⁻² Ω cm² at 100 A cm⁻² and a very small voltage penalty of 0.2–0.3 V compared to the conventional indium tin oxide contact LEDs. The low V _f penalty is caused by a higher turn on voltage, which is the smallest one among the MOCVD-grown TJs LEDs and comparable to the best molecular beam epitaxy-grown TJs LEDs. (paper)