■ Example of research topics ■
Growth of InGaAs(P) in a large-scale MOVPE reactor using TBAs and TBP for photovoltaic applications
H. Sodabanlu, K. Watanabe, M. Sugiyama, Y. Nakano
InGaAs(P) ternary and quaternary compounds have been extensively used in optical commination devices because their energy bandgaps can cover the operating windows, 1.3 and 1.55 µm wavelengths. Recently their usage have been extended to the photovoltaics application, especially multiple junction solar cells which 46% conversion efficiency of InGaP/GaAs/InGaAsP/InGaAs 4-junction structure has been reported. Hence, the development of InGaAs an InGaAsP subcells on InP substrates has become one of intensive research interests of III-V semiconductor solar cells. Our group has been successfully fabricated 0.74-eV InGaAs and 1.04-eV InGaAsP n-p solar cells in a planetary metalorganic vapor phase epitaxy (MOVPE) reactor. Tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) were utilized as alternative group V precursors to extremely hazardous arsine (AsH3) and phosphine (PH3). The further research topics are focusing on the fabrication of InGaAsP/InGaAs dual junction cells and the direct wafer bonding between GaAs and InP substrates for multijunction solar cells.
Fig. 1 Structure of 4-junction solar cell fabricated by direct wafer bonding
Fig. 2 (a) current-voltage characteristics under AM1.5 illumination and (b) external quantum efficiency spectra of the 0.74-eV InGaAs and 1.04-eV InGaAsP n-p solar cell