High peak-current AlGaAs tunnel junctions for 10-junction GaAs laser power converters

Laser power converters (LPCs) are the core photovoltaic devices that act as receivers in optical wireless power transmission systems. In these devices, tunnel junctions (TJs) are employed to vertically interconnect multiple absorption sub-cells in series to construct high-voltage multi-junction LPCs. This work systematically investigates the effects of the Al composition, growth temperature, and doping levels on the performance of AlxGa(1−x)As TJs. Furthermore, the performance of TJs employing different doping schemes (conventional doping, Si + Te co-doping, and delta-doping) and structural designs [quantum well (QW) insertion] was evaluated. For samples with Al compositions of 0%, 7%, 22%, and 28%, the maximum peak tunneling current densities reached 31.0k, 20.3k, 4.8k, and 0.5k A/cm2, respectively, while the lowest tunneling resistivities achieved 1.17 × 10−5, 1.08 × 10−5, 1.89 × 10−5, and 1.39 × 10−4 Ω cm2, respectively. The optimized Al0.28Ga0.72As TJ, featuring a hybrid structure of Si + Te delta-doping and QW insertion, exhibited a peak tunneling current density of 14.6k A/cm2 in the as-grown state and maintained 1.1k A/cm2 after annealing. By applying this TJ structure to a 10-junction GaAs LPC, a photovoltaic conversion efficiency exceeding 60% was achieved.