Comparison of the LEDs benefiting from built-in electric fields grown on Ga- and N-polar bulk GaN substrates

This study investigates the impact of growth polarity on the optical and electrical performance of GaN-based light-emitting diodes (LEDs) by comparing structures grown on N-polar and Ga-polar GaN bulk substrates. For a direct comparison, the Ga-polar LED utilized a bottom tunnel junction to align the built-in polarization field with the current flow, replicating the configuration of the N-polar LED. It exhibited an emission intensity over three orders of magnitude higher, despite having a similar layer composition to its N-polar counterpart. However, the N-polar LED featured a smoother surface and a lower turn-on voltage. The Ga-polar LED demonstrated lower differential resistance and superior quantum well optical quality, as indicated by the current density value at maximum EQE. Ga-polar LEDs with a bottom tunnel junction outperform N-polar devices in terms of emission intensity while maintaining the advantageous built-in field alignment typically associated with N-polar LEDs. This suggests that the inferior performance of N-polar LEDs stems from challenges in the epitaxy process on the N-side of the GaN crystal.