AlGaAs/GaInP heterojunction tunnel diode for cascade solar cell application

A p+‐AlGaAs/n+‐GaInP heterojunction tunnel diode with band gap Eg≊1.9 eV was fabricated by the atomic layer epitaxy growth. Doping levels of 1×1020 cm−3 and 5×1019 cm−3 were achieved in the p and n side of the diode using carbon and selenium, respectively. The diode can be used to interconnect the high and low band‐gap cells in the AlGaAs/GaAs cascade solar cell structure. For forward current of 20 A/cm2, which is the expected current density at 1000 suns operation, there is only ∼20 mV voltage drop across the tunnel junction. When annealed at 650 and 750 °C to simulate the growth of the top cell, the diode was still suitable for 1000 suns operation. This is the first reported tunnel diode fabricated in high band‐gap material systems that can be used as the connecting junction in the cascade solar cell structure operating at 1000 suns.