0.74/0.55-eV Ga/sub x/In/sub 1-x/As/InAsP/sub 1-y/ monolithic, tandem, MIM TPV converters: design, growth, processing and performance

Thermophotovoltaic (TPV) tandem converter technology is being explored in an effort to improve both the efficiency and power density of TPV systems. Inverted, tandem structures incorporate epitaxially grown 0.74-eV lattice-matched Ga/sub 0.47/In/sub 0.53/As and 0.55-eV lattice-mismatched Ga/sub 0.28/In/sub 0.72/As diodes. Additionally, a strategy has been developed to allow voltage matching between these two subcells. Performance modeling calculations show that, under typical operating conditions, the 0.74/0.55-eV tandem converter should outperform a 0.5-eV single junction converter by 15% on an efficiency basis and by 15% on a power-density basis. This paper will present details regarding the design, growth, fabrication, and electrical, optical, and structural characterization of voltage-matched tandem TPV devices.