Al0.3Ga0.7As/GaAs heterojunction tunnel diode for tandem solar cell applications

A p+‐Al0.3Ga0.7As/n+‐GaAs heterojunction tunnel diode was fabricated using Atomic Layer Epitaxy (ALE) growth technique. Background carbon doping of ∼1020 cm−3 was achieved in the p‐side of the diode by optimizing growth conditions such as V/III ratio, exposure times to reactant gases, and growth temperature. In the n‐side of the diode GaAs was doped with silane and doping concentrations as high as 7×1018 cm−3 were also achieved. The dopants are chosen to satisfy the high levels and low diffusion requirements. The diode can be used to interconnect the high and low band‐gap cells in the AlGaAs/GaAs cascade solar cell structure. The reactor used in this investigation is a commercial MOCVD system which has been specially modified for dual operation of ALE and MOCVD growth modes.