Modeling an InGaP/AlGaAs tunnel junction containing an AlAs diffusion barrier

Cost improvements in concentrated photovoltaic (CPV) systems can be achieved by operating at increased solar concentration. Current multijunction CPV systems are limited to about 1000× concentration by the performance of the tunnel junctions (TJ) which connect the subcells. The TJ requires materials which are doped in excess of 10¹⁹ cm^-3 in order to operate effectively, and so are susceptible to diffusion during the growth of subsequent layers. This paper considers a tunnel junction comprised of tellurium doped n⁺-InGaP and carbon doped p⁺-AlGaAs with a several monolayers of AlAs at the interface. The diffusion profile of the dopants was found and used to calculate the tunneling current through a junction. Due to uncertainty in the diffusion constants of C and Te in the three layers, the tunneling current was calculated for several values of Dt. The diffusion constant ratio in the AlAs was taken as a fraction of the diffusion constant in the other two layers. A significant increase in peak tunneling current was seen for Dt>1×10^-14 cm² when a three monolayer thick AlAs barrier was present.