Double Heterostructure GaAs Tunnel Junction for a AlGaAs/GaAs Tandem Solar Cell

Abstract
A double hetero (DH) GaAs tunnel diode which consists of a GaAs tunnel junction sandwiched between AlxGa1-xAs layers has been grown by molecular beam epitaxy, and its annealing characteristics studied. DH tunnel diodes have the advantage that a decrease in the tunnel peak current density due to annealing is greatly suppressed compared to conventional GaAs diodes without AlGaAs layers. In-depth profiles of dopants indicate that the AlGaAs layers act as blocking layers against Be diffusion, which causes a degradation of the diodes. An Al0.4Ga0.6As/GaAs tandem solar cell incorporating the DH tunnel junction as interconnectors has achieved a conversion efficiency of 20%.