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 SiNx 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 SiNx 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.