Type II heterojunction tunnel diodes based on GaAs for multi-junction solar cells: Fabrication, characterization and simulation

In this work, Molecular Beam Epitaxy (MBE) grown tunnel junctions (TJs) based on GaAs(Sb)(In) materials are experimentally and numerically studied. From simple GaAs TJs grown with various n-doping levels, we develop a semi-classical interband tunneling model able to quantify the magnitude of the tunneling current density, which shows that direct interband tunneling is the predominant tunneling mechanism in GaAs tunnel junctions instead of trap-assisted-tunneling mechanisms. Numerical simulations based on non equilibrium perturbation theory through Non Equilibrium Green's Functions (NEGF) and a multi-band kp hamiltonian that includes both gamma and L valleys were performed by the IM2NP (Marseille) and confirmed this result. In order to further improve the performance of the TJs, we are fabricating a type II tunnel heterojunction based on GaAsSb and InGaAs materials.