III-V Device Integration on Silicon Via Metamorphic SiGe Substrates

A range of high performance minority carrier devices have been successfully fabricated on Si virtual substrates where threading dislocation densities (TDDs) as low as1x10^6 cm^-2 are routinely achieved. Minority carrier lifetime data achieved on GaAs-on-Si layers exploiting this novel SiGe buffer approach to monolithic integration (ζ_p = 10.5 ns and ζ_n = 1.7ns) verifies the high III-V material quality. Single junction GaAs solar cells with high efficiencies for GaAs/Si of 18.1% under AM1.5-G illumination were demonstrated. Further exploiting the novel GaAs/Si material quality, even more complex minority carrier devices including dual-junction solar cells and LEDs were fabricated, yielding high performance consistent with the high III-V/Si mobilities. In both cases, certain device metrics on SiGe outperformed identical GaAs monolithic devices. Finally, a visible laser on Si was achieved, demonstrating the success and further potential of this III-V/Si integration methodology

Evolution of the silicon bottom cell photovoltaic behavior during III-V on Si multi-junction solar cells production

The evolution of the Si bulk minority carrier lifetime during the heteroepitaxial growth of III-V on Si multi-junction solar cell structures via metal-organic vapor phase epitaxy has been analyzed. Initially, the emitter formation produces important lifetime degradation. Nevertheless, a progressive recovery was observed during the growth of the metamorphic GaAsP/Si structure. A step-wise mechanism has been proposed to explain the lifetime evolution observed during this process. The initial lifetime degradation is believed to be related to the formation of thermally-induced defects within the Si bulk. These defects are subsequently passivated by fast-diffusing atomic hydrogen -coming from precursor (i.e. PH3 and AsH3) pyrolysis- during the subsequent III-V growth. These results indicate that the MOVPE environment used to create the III-V/Si solar cell structures has a dynamic impact on the minority carrier lifetime. Consequently, designing processes that promote the recovery of the lifetime is a must to support the production of high-quality III-V/Si solar cells