Epitaxial growth of III-V compounds on (111) silicon for solar cells

摘要

A multi-junction device can be used as a high efficiency solar cell, laser, or light-emitting diode. Multiple epitaxial films grown over a substrate have very low defect densities because an initial epitaxial layer is a coincidence-site lattice (CSL) layer that has III-V atoms that fit into lattice sites of Silicon atoms in the substrate. The substrate is a Si (111) substrate which has a step height between adjacent terraces on its surface that closely matches the step height of GaAs (111). Any anti-phase boundaries (APBs) formed at terrace steps cancel out within a few atomic layers of GaAs in the (111) orientation since the polarity of the GaAs molecule is aligned with the (111) direction. A low CSL growth temperature grows GaAs horizontally along Si terraces before vertical growth. Tunnel diode and active solar-cell junction layers can be grown over the CSL at higher temperatures.