Fig. 1. (a) Schematic illustration of the tunnel junction LED structures. (b) Simulated equilibrium band diagram for a representative LED using a 5 nm GaN layer within the tunnel junction. The different layers used in the structure are labelled and shown with different colors.

Fig. 2. (a) HAADF-STEM overview of cross-sectional AlGaN multilayers shows the complete device structure consistent with the device design. (b) High-resolution HAADF-STEM of the p-AlGaN/GaN/n-AlGaN tunnel junction shows crystalline epitaxial growth with sharp interfaces for enhanced hole injection by tunneling. (c) Atomic-resolution HAADF-STEM of Al0.6Ga0.4N quantum wells coupled to Al0.85Ga0.15N barriers with sharp epitaxial interfaces for carrier confinement.

Fig. 3. (a) I–V characteristics of tunnel junction LED Samples A and B, with 2.5 nm GaN layer width and different thicknesses, 50 and 150 nm respectively, of top n+-AlGaN contact layer. (b) I–V characteristics of Samples B, C, and D grown with the same thickness of top n+-AlGaN but different GaN layer widths of 2.5, 5, and 10 nm, respectively. Variations of (c) EQE and (d) WPE with injected current density, for Samples B, C, and D.

Fig. 4. I–V characteristics of an optimized tunnel junction LED from Sample E with a GaN layer thickness of 5 nm and top n-AlGaN contact layer thickness ∼480  nm.

Fig. 5. (a) Electroluminescence spectra measured at different injection currents for a representative tunnel junction LED. Inset shows an electroluminescence spectrum measured at 25  A/cm2 current density with the intensity in log scale. (b) Variations of peak position (red circles) and spectral linewidth (black squares) versus injected current density.

Fig. 6. Variations of (a) EQE and (b) WPE with injected current density for an LED from Sample E.