Kyma goes non-polar with native GaN substrates
GaN specialist Kyma Technologies has developed a new range of non-polar and semi-polar nitride substrates that should lead to higher-performance wide-bandgap devices.
In devices grown on top of non-polar GaN, the usual electric fields that result from the intrinsic polarity of the substrate material are eliminated, while in semi-polar material they are reduced.
This means that GaN-based optoelectronic devices can operate at higher efficiencies. One high-profile fan of the non-polar approach is Shuji Nakamura. Along with his University of California, Santa Barbara colleagues, the famed researcher has been working on non-polar device structures grown on r-plane sapphire substrates.
According to UCSB's Paul Fini, the non-polar a-planes and m-planes in GaN feature an equal number of gallium and nitrogen atoms in the growth direction, meaning that there is no net electric field induced in devices.
Non-polar and semi-polar optoelectronic devices should operate at much higher drive currents and be more reliable than conventional devices. This is because of an improvement in p-type conductivity, which reduces heating effects in the active region of the diodes.
Kyma adds that improved p-type doping efficiencies in non-polar GaN could benefit all kinds of optoelectronic and electronic devices.
"By eliminating the presence of induced charge, non-polar and semi-polar GaN substrates may enable the development of enhancement-mode GaN transistors," said the company.
"We believe that non-polar devices will see quite rapid commercialization," Fini told Compound Semiconductor last year. "After device film growth has been optimized, all subsequent processing would be nearly identical to conventional devices."
Kyma has also released some new semi-insulating GaN substrates with a lower defect level than before. Ed Preble, the company's VP of engineering, said that an optimized process had drastically cut down on the conductive regions in Kyma's GaN boules. "We realized we needed to eliminate certain defects," he said.
Customers developing devices on the native material should see better high-frequency transistor performance and improved electrical isolation between adjacent devices, added Preble.
