UC Berkeley

The growth and characterization of GaAs nanowires and GaNPAs thin-films is discussed within the context of finding a material system that is suitable as an intermediate band solar cell (IBSC) absorber. The IBSC is an attractive concept proposed to exceed the Shockley-Queisser detailed balance limit for photovoltaic efficiency. These solar cells have an additional intermediate band, allowing for the absorption of below bandgap photons, thus resulting in an increase in photocurrent and higher efficiency. Suitable materials systems for the implementation of the IBSC concept, however, are presently lacking. Recent work on the highly-mismatched alloy (HMA) GaAsN has shown that the unique features of the electronic band structure demonstrate optical activity of three energy bands and have led to the realization of a proof-of-concept IBSC. GaAsN, however, is not without shortcomings. Another HMA material, GaNPAs, which offers a wide range of bandgap tunability and is better matched to the solar spectrum is proposed. This work covers the optical characterization of both GaAs nanowires and GaAsPN using traditional visible-light semiconductor characterization techniques including optical absorption spectroscopy, photo-modulated reflectance, steady-state photoluminescence, and spectral photoconductivity. Additionally, photovoltaic devices based on GaNPAs are demonstrated and assessed as potential IBSCs.