Multiphoton Sub-Band-Gap Photoconductivity and Critical Transition Temperature in Type-II GaSb Quantum-Dot Intermediate-Band Solar Cells

Abstract

Multiphoton transitions in GaSb/GaAs quantum-dot intermediate-band solar cells are investigated at variable temperature and excitation intensity. A transition temperature is observed that corresponds to the crossover between quantum-dot intraband transitions dominated by thermal escape due to infrared photogeneration. The transition temperature follows an Arrhenius relation with an activation energy of 220 meV that corresponds to the energy barrier observed by holes in the quantum dots. The transition temperature is in the range of 160-225 K for the temperature range studied, significantly higher than observed in previous type-I quantum-dot systems. These results illustrate the potential of type-II structures with deep confinement potentials and strong intraband absorption for future intermediate-band solar cells and quantum devices.