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 mm(2)) and micro-size InGaN light-emitting diodes (LEDs and mu LEDs). 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 mm(2) LEDs and mu LEDs, the V-f is independent on the SAG aperture space varied from 3 to 8 mu m when the Si-doping level in the n(+)GaN layer is as high as 1.7 x 10(20) cm(-3). The optimized TJ LEDs exhibit a comparable differential resistance of 1.0 x 10(-2) omega cm(2) 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.