Analysis of impurity diffusion from tunnel diodes and optimization for operation in tandem cells

Abstract The tunnel diode has been applied as an interconnector in monolithic devices such as tandem solar cells. However, thermal degradation due to impurity diffusion is often observed due to growth at above about 600°C. In this study, the impurity diffusion from highly doped tunnel junctions after annealing has been analyzed, and it has been suggested that carbon has the advantage of a low diffusion coefficient as the p-type impurities. Furthermore, the thermally stable double hetero (DH) structure GaAs tunnel diodes which have been proposed in our previous work have been optimized. The thermal degradation is greatly suppressed by using a DH-structure which consists of a GaAs tunnel diode sandwiched between Al x Ga 1− x As layers, and as a result, a higher tunnel peak current density can be achieved by optimizing the impurity concentration and DH composition.