Improvement of GaP crystal quality and silicon bulk lifetime in GaP/Si heteroepitaxy

The GaP crystal quality and Si bulk lifetime of GaP/Si heterostructures, grown by molecular beam epitaxy, are investigated. The Si bulk lifetime is reduced by over one order of magnitude after thermal deoxidation at high temperatures (>700 °C). This significant reduction of the bulk lifetime is not observed when 150 nm-thick SiN_x film is present on the backside of Si wafer, which can act as a diffusion barrier and/or getter. In addition, a 15 nm-thick GaP layer grown on the front side of Si wafer with SiN_x on the backside shows a high crystal quality of GaP with a low crystalline defect density of 1.1 × 10⁵ cm⁻². Moreover, the Si bulk lifetime is determined to be 1.83 ms with a-Si:H passivation at an injected minority-carrier density of 1 × 10¹⁵ cm⁻³, indicative of no bulk lifetime degradation. The high crystallinity of GaP and improved Si bulk lifetime are beneficial to improve photovoltaic device performance of III–V compound solar cells integrated with Si solar cells.