Demonstration of N-polar III-nitride tunnel junction LED

In this study, we have demonstrated the N-polar III-nitride tunnel junction (TJ) light-emitting diode (LED). The LED was grown on the N-polar GaN template on sapphire substrates by metalorganic vapor phase epitaxy. The growth started with the n-GaN cladding layer whose doping condition was optimized by the periodic doping method and then the InGaN/GaN quantum well active region. Subsequently, the TJ was grown comprising a graded p-AlGaN layer, a thin undoped Al0.4Ga0.6N interlayer, and the topmost n-GaN layer. The I-V measurement show that the device resistance of the TJ LED was significantly reduced compared to the reference LED without the TJ due to enhanced hole injection. The electroluminescence measurement manifested that the emission and the external quantum efficiency of the TJ LED were greatly enhanced by ~70% compared with the reference LED. This work demonstrates that the TJ devices can be realized amid N-polarity that is promising for high-performance devices operating at various wavelength.