17 March 2020
Eta develops 4” semi-insulating GaN wafers
Eta Research of Lingang Free Trade Zone, Shanghai, China, which was founded in 2015 to develop free-standing gallium nitride (GaN) wafers, has developed semi-insulating 4” GaN. The firm claims to be first to commercially develop semi-insulating free-standing GaN wafers at this size.
Eta uses the hydride vapor phase epitaxy (HVPE) method to produce GaN wafers. To compensate the unintentional n-type dopants, a deep-level co-doping strategy was used to achieve high resistivity. Whereas iron doping has been the most prevalent choice for semi-insulating GaN, Eta uses carbon doping. Secondary-ion mass spectroscopy (SIMS) data shows the carbon concentration to be in the range of 5E17–3E18/cm3. The unintentional n-type dopants of oxygen and silicon are below 1E17/cm3. The resistivity has been measured by Hall measurement and I-V curve, which result in room-temperature resistivity greater than 1E9Ω-cm.
The crystal and wafer quality specifications of the semi-insulating GaN wafers remains the same as the company’s n-type GaN wafers. XRD rocking curves of both the (002) and (102) are <100 arcsec and typically 50–60 arcsec. The dislocation density has been measured by cathodo-luminescence (CL) to be 1E6/cm2. The lattice radius of curvature is greater than 10m. Total thickness variation (TTV) and bow can be controlled within 30μm for 100mm wafers. The surface has an epi-ready polish with roughness <0.3nm for a 10μm x 10μm atomic force microscope (AFM) measurement and <1.0nm for 239μm x 318μm optical interferometry measurement.
The market for semi-insulating GaN wafers is for RF HEMT devices. The RF device market is experiencing high growth due to the implementation of 5G and other wireless communication applications. GaN is a useful semiconductor material for high power and high frequency RF devices, but the industry is almost exclusively producing GaN HEMTs on silicon carbide (SiC) substrates. GaN-on-GaN RF devices will have lower dislocation density device layers and no buffer layer is required, so the firm expects that higher power and better performance will result from RF devices made on GaN substrates.
“Due to the very limited supply, size and quality of semi-insulating GaN wafers, there has only been a limited body of research work conducted on GaN RF devices grown homoepitaxially,” says CEO Troy Baker. “We plan to work with customers to prove the value proposition of GaN wafers for RF devices. We are very optimistic about the performance gains that could be made using semi-insulating GaN wafers,” he adds. “The wafers are currently available for sale and the company is building new HVPE reactors with carbon doping capability. In addition, we are able to provide MOCVD [metal-organic chemical vapor deposition] epi layers on GaN wafers.”
Each wafer will be shipped with a detailed wafer inspection form. Standard products are 2” and 4” wafers, and customized sizes are available as well.