Fabrication of resonant tunneling structures for selective energy contact of hot carrier solar cell based on III–V semiconductors

In this study, double barrier (DB) resonant tunneling structures based on III-V semiconductors were fabricated and its potential for selective energy contacts (SEC) of hot carrier solar cells was evaluated. An AlGaAs/GaAs/AlGaAs quantum well (QW) based DB structure was fabricated by molecular beam epitaxy (MBE) on GaAs (001) substrate, which acts as SEC for electrons. The current-voltage (I-V) characteristics under light excitation shows a voltage shift of tunneling current tail to a lower bias and this result demonstrates an extraction of high energy photoelectrons through the DB structure. Furthermore, properties of quantum dot (QD) resonant tunneling structures were investigated as an ideal SEC. Photoluminescence (PL) measurements showed that controllable PL peak energy range of InAs QDs/Al_xGa_1-xAs structures well corresponds to the required carrier extraction energy, which is the difference between electron and hole extraction energies of SECs, for high conversion efficiency. In addition, resonant tunneling current peaks originate from the InAs QDs embedded in an Al_0.6Ga_0.4As barrier are clearly observed for both forward and reverse bias by conductive atomic force microscope (C-AFM). These results indicate that InAs QD/Al_xGa_1-xAs resonant tunneling structures are suitable for designing the optimum SEC structure.