In collaboration with semiconductor recycling company III/V-Reclaim, researchers at the Fraunhofer Institute for Solar Energy Systems ISE (Fraunhofer ISE) have produced high-quality indium phosphide on gallium arsenide substrates (InP-on-GaAs wafers) with up to 150-mm diameter. According to the researchers, the wafers can effectively replace classic indium phosphide in a variety of applications, offering a scalable pathway to lower cost. The team developed a process to deposit a thin layer of high-quality InP on GaAs. Following a special surface treatment, these wafers can then be delivered epi-ready, enabling customers to directly grow III-V epitaxial structures and manufacture high-performance InP-based semiconductor devices, according to the scientists. Researchers developed a process to deposit a thin layer of high-quality indium phosphide on gallium arsenide substrates with 100- and 150-mm diameter. These engineered wafers can be used as a direct replacement for classical InP substrates. Courtesy of Fraunhofer ISE/Carmine Pellegrino. “Companies can use our new InP-on-GaAs substrates to manufacture high-efficiency devices”, said Carmine Pellegrino, project manager at Fraunhofer ISE. “However, it costs much less than InP and there are no limitations in terms of scalability to even 8-inch diameter wafers.” The application of InP on GaAs is challenging, the researchers said, because defects occur during the growth of the InP, which can degrade the performance of the final device. This was avoided by incorporating a series of “metamorphic buffer layers” and by subjecting the fully grown InP-on-GaAs wafer to a special chemical-mechanical polishing step. Following this process, the wafers appeared shiny while exhibiting very low surface roughness and defect densities below 5 × 106 cm-2. The researchers tested the material quality and performance of the InP-on-GaAs wafers and compared them to standard indium phosphide substrates, achieving favorable results, according to Frank Dimroth, head of the III-V photovoltaics department at Fraunhofer ISE. “Photovoltaic cells fabricated on our engineered wafers achieve open-circuit voltages comparable to reference devices on prime InP wafers. The performance is consistently uniform across the entire 6-in. wafer, enabling reliable, high-yield production," he said. As part of a series of experiments, the researchers have so far produced InP-on-GaAs wafers with diameters of 4 and 6 in., with no obstacles foreseen for a future transition to 8-in. Classic InP substrates, on the other hand, are currently available in sizes from 2 to 4 in., with a 6-in. version only recently becoming available. This is because GaAs substrates are more robust and formats with a diameter of up to 8 in. are already well established in the semiconductor industry. The higher stability of GaAs also makes it possible to produce thinner wafers, leading to cost savings and less material usage. “Our technology naturally benefits from having gallium arsenide as a basis,” Pellegrino said. “The production costs of the new substrates are significantly lower than those of indium phosphide wafers, with a savings potential up to 80% in mass production according to our first calculations. In addition, our approach bypasses constraints on the supply of indium phosphide.”
