Fig. 1. (Color online) (a) Schematic diagram of the device structure including GaN/InGaN/GaN TJ. (b) Equivalent circuit diagram of the device.

Fig. 2. (Color online) XRD ω−2θ patterns of the three samples (a) S₁ , (b) S₂ , (c) S₃. The black curve represents the experimental curve, while the red curve represents the simulation curve.

Fig. 3. (Color online) Surface AFM images of the three samples (a) S_1, (b) S₂, (c) S₃.

Fig. 4. HRTEM image of the tunnel junction.

Fig. 5. (Color online) (a) I–V curves of the samples, the doping concentration at the TJ of the samples varies, and (b) the change of differential resistance at forward current density.

Fig. 6. (Color online) (a) I–V curves of the samples, In content of the InGaN layer at the tunnel junction changes, (b) the change of differential resistance at forward current density.

Fig. 7. (Color online) I–V curves of the samples, thickness of InGaN layer at tunnel junction varies.

Fig. 8. (Color online) I–V curves of the samples, doping in InGaN layers at tunnel junctions changes.