| Summary: | 碩士 === 元智大學 === 光電工程學系 === 100 === Due to the awareness of natural resources shortage and energy crisis, nations around the world all devoted in the development of alternative energy source. Solar power has the advantages of cleanness and abundance; therefore how to exploit this energy efficiently has become the most important development target. The novel idea of separated photo-excited carriers by modifying the energy band structure from type-I to type-II structure via antimony element is introduced. In type-II structure, the photo-excited electrons and holes are separate confined in QDs and overgrown layer, respectively. Therefore, this configuration can help reduce the carrier radiative recombination and Auger effect.
Besides, Physical Review Letters, 78 point out the intermediate band formation in vertical align quantum dot structure will increase absorption efficiency with low-energy photons. Intermediate band can also make carriers transfer to P/N junction quickly, result in the enhancement of solar cell conversion efficiency. The solar cells conversion efficiency influence factor can be separate into four parts：p layer、n layer、carrier lifetime and diffuse length. In this work, we focus on prolonging carrier lifetime to improve solar cell efficiency. Antonio Luque research group have already confirmed that long carrier lifetime reduce the opportunity of electron-hole recombination to improve solar cell efficiency.
Carrier dynamic of the vertically aligned InAs/GaAsSb quantum dot structure is analyzed by Time-Resolved Photoluminescence (TRPL) in this work. Structure of InAs columnar quantum dots with GaAsSb overgrown layer is first proposed for elongated carrier lifetime in photovoltaic application. Both the tunneling effect of columnar quantum dot structures and the type-II energy band alignment can increase the carrier lifetime in this novel structure. Power dependent PL and TRPL measurement are employed to characterize the optical properties of typical InAs/GaAs type-I and InAs/GaAsSb type-II vertically aligned quantum dot structure. The longest carrier lifetime is demonstrated in the columnar InAs/GaAsSb type-II band structure.
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