Fig. 1. HR-XRD RSM near the AlN (10.5) reflex of a TJ LED heterostructure. Peaks corresponding to the individual layers are labeled in the graphic.

Fig. 2. Differential resistivity as a function of the bandgap and Al mole fraction at the TJ interface as reported for III-nitride LEDs [15,18,26–35" target="_self" style="display: inline;">–35]. Open and full symbols represent MBE- and MOVPE-grown heterostructures, respectively.

Fig. 3. Spectral power density versus emission wavelength plot for a 232 nm TJ LED (A=0.15  mm2) measured through the bottom substrate (solid line) and top surface (dotted line) at a dc current of 5 mA. The inset shows a UV-sensitive microscopy image of a square-shaped frame top n-contact (A=0.04  mm2) measured at 5 mA through the top surface.

Fig. 4. (a) LIV characteristics and EQE of a TJ LED measured through the bottom substrate (solid lines) and the top surface (dashed lines). Far-field emission pattern measured on-wafer of (b) the bottom and (c) the top hemispheres at a constant current of 5 mA. The black dashed lines in (b) and (c) indicate the detectable emission by the bottom and top EL setup as shown in (a).

Fig. 5. (a) LIV characteristics and EQE of a TJ LED with an aluminum reflector on the top surface as measured through the bottom substrate. (b) Far-field emission pattern measured on-wafer of the bottom hemisphere at a constant current of 5 mA. The black dashed line indicates the detectable emission by the bottom EL setup as shown in (a).

Fig. 6. Schematic TJ LED heterostructure and simulated LEE of (left) a TJ LED without aluminum reflector, (center) a TJ LED with large-area aluminum reflector, and (right) a TJ LED with large-area V/Al n-contact.

Fig. 7. On-wafer measured bottom LIV characteristics in cw (solid lines) and pulsed mode operation (bullets) of a tunnel heterojunction LED (A=0.15  mm2) with aluminum reflector.