Silicon-based semiconductors are approaching their performance limits, so researchers are investigating materials such as gallium nitride (GaN) as potential replacements. A team of engineers from Cornell, Notre Dame and the semiconductor company IQE has created GaN power diodes capable of serving as the building blocks for future GaN power switches.
Alas, GaN is prone to defects and reliability issues, and current GaN-based devices often operate at a fraction of what GaN is truly capable of. In “Near unity ideality factor and Shockley-Read-Hall lifetime in GaN-on-GaN p-n diodes with avalanche breakdown,” published in the journal Applied Physics Letters, the team describes how they worked with devices based on GaN with low defect concentrations to probe GaN’s performance limits.
“Our engineering goal is to develop inexpensive, reliable, high-efficiency switches to condition electricity – from where it’s generated to where it’s consumed within electric power systems – to replace generations-old, bulky, and inefficient technologies,” said co-author Zongyang Hu. “GaN-based power devices are enabling technologies to achieve this goal.”
The researchers developed a “diode ideality factor” to quantify the deviation of the device’s current-voltage characteristics from the ideal. “One parameter we used to effectively describe the defect level in a material is the Shockley-Read-Hall (SRH) recombination lifetime,” Hu said. “The lower the defect level, the longer the SRH lifetime.”
The team found unexpectedly low differential-on-resistance of the GaN diode. “It’s as if the body of the entire p-n diode is transparent to the current flow without resistance,” he said. “We believe this is due to high-level injection of minority carriers and their long lifetime, and are exploring it further.”
This work is the first report of GaN p-n diodes with near-ideal performance in all aspects simultaneously: a unity ideality factor, avalanche breakdown voltage, and about a two-fold improvement in device figure-of-merits over previous records.
“Our results are an important step toward understanding the intrinsic properties and the true potential of GaN,” Hu noted. “And these achievements are only possible in high-quality GaN device structures (an effort led by IQE engineers) prepared on high-quality GaN bulk substrates and with precisely tuned fabrication technologies (an effort led by Dr. Kazuki Nomoto, a research associate at Cornell University).”