Thermal Stability of III-V Materials Printed to Low Cost Handles

Virtual substrates formed by integrating high quality, micro-scale III-V epitaxial template layers with cheap handle materials using transfer printing offer a pathway to very low cost III-V growth substrates for microscale device epitaxy. However, understanding the impact of coefficient of thermal expansion (CTE) mismatch on the robustness of the bond between the handle and the epitaxially grown materials is very important for potential commercialization of virtual substrate technologies. Materials such as silicon, quartz, sapphire, and alumina ceramic offer varying CTE mismatch values and are cost effective as targets for virtual substrate handles. In this paper we describe two separate experiments that examine the reliability of the bond interface between GaAs and non-native substrates using a statistical analysis of near-IR microscope images to compare void formation before and after thermal cycling. First, multijunction GaAs-based solar cells were printed to a silicon substrate and cycled between 50-250° C. The considerable CTE mismatch existing between silicon and III-V cell materials caused problematic delamination of printed materials with existing voids. Second, unprocessed GaAs chiplets were printed to sapphire and cycled between 65-270°C. No visible delamination occurred after 20 cycles, indicating no degradation in bond quality. Successful cycling at higher temperatures, such as those observed during growth, would further indicate that transfer printed virtual substrates on low-cost handles are a suitable candidate for regrowth experiments.