Authors: Yudai Shimizu, Keitaro Ikejiri, Hiroki Tokunaga
Abstract
In recent years, the growth of nitride semiconductors containing rare-earth elements (REE) has attracted attention as a means of achieving useful properties not available in conventional nitride semiconductors. As growth methods for REE-containing nitride semiconductors, magnetron sputtering, molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), ion implantation, and other methods have been proposed. Among these, the metalorganic chemical vapor deposition (MOCVD) method excels in terms of mass productivity, precise control of structure, and crystal quality. However, the inherently low vapor pressure of REE metalorganic precursors is a significant obstacle to REE supply in MOCVD systems. In conventional metalorganic supply systems, maintaining a stable supply of RE precursors is challenging due to the aggregation of the precursors in cold spots along the supply path. This is attributed to an insufficient supply of RE precursors, which results in a significant reduction in supply efficiency. To address this issue, we have developed a low vapor pressure precursor supply MOCVD system (SR4000-HT-LV, Taiyo Nippon Sanso) that considers maintaining sufficient temperatures throughout the entire supply path from the equipment design stage.
In this presentation, we report on the growth of AlScN using tris(cyclopentadienyl)scandium (Cp3Sc) as a precursor of Sc, which has a vapor pressure about five orders of magnitude lower than that of the Al precursor (trimethylaluminum). Since AlScN is attracting attention as a next-generation material for high-frequency applications, structures was fabricated for AlScN/GaN HEMT applications in this demonstration. X-ray diffraction measurements confirmed the successful growth of AlScN that is nearly lattice matched to GaN (AlScN: a = 0.319 nm, GaN: a = 0.319 nm). In addition, the Sc concentration in the GaN layer grown after AlScN growth and subsequent cleaning was below the detection limit in SIMS measurements. The results show that there are no memory effects between growth batches. In conclusion, it has been demonstrated that our LV supply unit is capable of supplying precursors while minimizing residues in the supply system.
