Uniformity of GaAs Solar Cells Grown in a Kinetically-Limited Regime by Dynamic Hydride Vapor Phase Epitaxy

We demonstrate solar cell devices grown on 50 mm diameter GaAs substrates by dynamic hydride vapor phase epitaxy (D-HVPE). In contrast to our prior D-HVPE devices, grown at 650 °C in a transport-limited regime, these devices were grown at 700 °C in a kinetically-limited growth regime in which the growth rate uniformity is controlled by thermally-activated surface reactions. These devices exhibit open-circuit voltages up to 1.07 V, nearly identical performance to the devices grown at lower temperature in a different growth regime. We evaluate the uniformity of device performance and find only a 1% variation in absolute, device efficiency across the majority of the wafer in devices without anti-reflection coating. We analyze the GaAs and GaInP thickness uniformity and GaInP compositional uniformity, using high-tresolution x-ray diffraction mapping, and find that any non-uniformity in device efficiency is not related to variations in these structural parameters. We combine three-dimensional computational fluid dynamics modeling of our reactor with a kinetic model for GaAs growth, and use the combined model to predict spatial GaAs growth rate over a 50 mm wafer area. We compare these predictions with experimental data from our D-HVPE reactor and find excellent agreement. We use the model to the gain insight into the specific mechanisms that control GaAs spatial uniformity in the kinetically-limitedgrowth regime. These results suggest a large parameter window for the growth of high-performance optoelectronic devices by D-HVPE, possibly with large area uniformity.