Engineers have created new high-power electronic devices that are more energy efficient than their predecessors. The devices are made possible via a unique technique for “doping” gallium nitride (GaN) in a controlled way.
“Many technologies require power conversion — where power is switched from one format to another,” said Dolar Khachariya, Senior Scientist at Adroit Materials, Inc., and former Ph.D. student at North Carolina State University. “For example, the technology might need to convert AC to DC, or convert electricity into work — like an electric motor. And in any power conversion system, most power loss takes place at the power switch — which is an active component of the electrical circuit that makes the power conversion system.
“Developing more efficient power electronics like power switches reduces the amount of power lost during the conversion process. This is particularly important for developing technologies to support a more sustainable power infrastructure, such as smart grids.
The work pays off two-fold: Not only can it reduce energy loss in power electronics, but it can also make the systems for power conversion more compact compared to conventional silicon and silicon carbide electronics, said Ramón Collazo, Associate Professor of Materials Science and Engineering at NC State.
“This makes it possible to incorporate these systems into technologies where they don’t currently fit due to weight or size restrictions, such as in automobiles, ships, airplanes, or technologies distributed throughout a smart grid,” he added.
Put simply: The researchers engineered impurities into specific regions on GaN materials to selectively modify the electrical properties of the GaN strictly in those regions. They’ve demonstrated how this technique can be used to create actual devices.
“We’ve demonstrated that you can selectively dope GaN to create functional Junction Barrier Schottky (JBS) diodes, and that these diodes are not only functional, but enable more power efficient conversion than JBS diodes that use conventional semiconductors,” said Collazo. “For example, in technical terms, our GaN JBS diode, fabricated on a native GaN substrate, has record-high breakdown voltage (915 V) and record low on-resistance.”
Here is Tech Briefs interview (edited for clarity and length) with Khachariya and Spyridon Pavlidis, Assistant Professor, Department of Electrical and Computer Engineering, North Carolina State University.
Tech Briefs: What spurred this research?
Khachariya: Due to the superior material properties of GaN over Si and SiC, the power devices made with GaN would be more energy efficient due to low resistances, higher breakdown voltages, and higher switching frequency. However, selective-area doping is necessary to obtain power devices, such as JBS, JFETs, and MOSFETs, in GaN material systems. Ion implantation is one of the basic tools for semiconductor device fabrication, and as such, any maturing semiconductor system should be capable of being processed in this form. So far, GaN did not possess a robust ion implantation toolbox that allowed for reliable implantation control and activation. We have developed successful and reliable ion-implantation and activation techniques in GaN. This technique allowed us to obtain kV-class blocking GaN JBS diodes on native GaN substrates.
Tech Briefs: What’s the next step in your research?
Khachariya: As shown in our manuscript, we demonstrated successful GaN JBS diodes with almost 1kV blocking capabilities. In the future, we would further increase the breakdown capabilities of these GaN JBS diodes (~5 kV) by increasing the drift layer thickness.
Tech Briefs: When will this technology be commercially available?
Khachariya: Major technological challenges in GaN devices were robust ion implantation and activation techniques and large area substrates. We demonstrated in our manuscript that successful implantation and activation could be achieved to obtain selective-area doping. Due to the enormous investments in GaN LEDs, we believe that with time, the size of the GaN substrates will also increase in the near future. Thus, we believe that this technology should be commercially available soon.
Tech Briefs: Will there be a large market for it? Will it catch on?
Pavlidis: At the center of any power electronic system are power switches, whose primary function is to convert power efficiently. Since a considerable amount of power losses occurs at these power switches, high-performance semiconductor power switches are required for achieving compact and energy-efficient power systems. The improved efficiency would provide not only economic benefits but also reduce pollution.
Reducing energy consumption would eliminate the emissions of trillions of pounds of carbon dioxide, which would help mitigate climate change. Thus, developing energy-efficient power systems is important. GaN has superior material properties over Si and SiC; thus, the devices would be more energy efficient. As selective area doping can be achieved in GaN, we believe various device architectures are possible in GaN. Thus, there will be a large market for it.
Tech Briefs: How will this impact the industry?
Pavlidis: At the application level, we hope this advancement will yield energy and economic savings by boosting the efficiency of converters. Moreover, these devices have the potential to reduce the size and weight of power electronic modules, which is not only a benefit to current applications but also opens the door to new applications, such as space-deployable electronics.
At the device level, we hope this work sheds light on the progress being made on vertical GaN power device technologies. These devices have the potential to compete with and surpass the performance of both conventional silicon as well as emerging silicon carbide devices. With Mg implantation being added to the processing toolbox, a new generation of GaN devices can now be pursued.
Tech Briefs: Are you working on other such advances? Projects?
Pavlidis: Our team is actively involved in many aspects of GaN device technologies for next-generation power devices. One other, and particularly novel, effort involves the development of GaN-based superjunction devices. Superjunctions allow for the losses to be reduced below conventional limits but have been quite difficult to realize in GaN technology. We have recently developed a unique approach to this that leverages the specific material properties of GaN, and the results are promising so far. If we can hit our target, it would represent a major technological advantage for GaN over competing technologies.