A p+‐AlGaAs/n+‐GaInP heterojunction tunnel diode with band gap Eg≊1.9 eV was fabricated by Atomic Layer Epitaxy growth mode using carbon and selenium as the p‐ and n‐type dopants, respectively. The doping levels of 1×1020/cm3 and 5×1019/cm3 were achieved both in the p‐ and n‐side of the diode, respectively. The diode can be used as the interconnection of the high and low band gap cells in the AlGaAs/GaAs cascade solar cell structure. At the forward current of 15 A/cm2, which is the expected current density at 1000 suns operation, there is only ∼17 mV voltage drop across the tunnel junction. This is the first reported tunnel diode fabricated in high band gap material systems, with performances that exceed the best reported GaAs tunnel diode.