One major roadblock is that the best substrates for ensuring high-quality growth of electronic materials tend to be incompatible with critical design goals, such as low thermal resistance and cost, according to an article titled, “GaN on Anything” in Compound Semiconductor Magazine’s January/February issue. To tackle this issue head on, the authors from the Naval Research Laboratory recently developed a versatile technique that releases III-N devices from their costly SiC substrates. This technology has the potential to form freestanding GaN and AlN.
"The pivotal enabler is a thin layer of niobium nitride, Nb2N. It has several important attributes: a close lattice-match to GaN; temperature-compatibility with III-N growth; and a selective etch character over GaN, AlN and SiC. Using Nb2N as a sacrificial layer allows simple processing, based on standard fabrication equipment, for the lift-off and transfer of III-N devices to any desired substrate after completing front-side processing and yield screening," state the authors.
Solid-state (or LED) lighting and wireless data transmitters for cell phone base stations are two examples where GaN has made a considerable impact over the past few years. Power switching components for solar inverters and electric vehicles are also moving towards GaN technology due to its ability to improve efficiency.
"GaN technology ultimately saves energy compared to incumbent technologies and can typically be packaged in smaller and lighter form factors," said Dr. David Meyer, U.S. Naval Research Laboratory (NRL) section head for wide bandgap materials and devices in the Electronics Science and Technology Division.
During the 90s, the Navy and other DoD agencies invested a large amount of funding in basic research of GaN technology for RF wireless technology. Over the past few years it has successfully graduated from the research lab and is now used in military systems such as the Air and Missile Defense Radar (AMDR) and Next Generation Jammer.
Meyer's group at NRL has continued to push nitride materials research forward and recently made an important breakthrough in the ability to grow thin films of a transition metal nitride called niobium nitride (Nb2N). The thin crystalline material has a similar structure to GaN; however, its electrical and physical properties are dramatically different. For instance, Nb2N is metallic instead of semiconducting and can become superconductive at cryogenic temperatures.
"We have determined that Nb2N has several unique properties that can lead to the realization of new microelectronic devices and circuits," said Meyer.
One property of the new material is how it dissolves away in a reactive gas, while leaving nearby GaN electronics untouched. By inserting a thin layer of Nb2N between a GaN transistor, LED, or circuit and the substrate the material is grown on, Meyer and his team can perform a patent-pending lift-off technique, which allows it to be transferred onto nearly anything.
"We have this method and it's really flexible. We anticipate that there are several applications that would benefit from having GaN technology integrated at the device or circuit level," said Meyer.
"We are very excited to be exploring the impact that Nb2N can have on III-N applications and technology. When applied to ELO and transfer, Nb2N offers a number of important advantages over competing lift-off methods involving ion implantation or photo-electrochemical etching. Aside from producing an atomically-smooth, bonding-ready released device or circuit backside, our ELO process can recycle substrate material indefinitely, potentially leading to significant cost savings," concluded Meyer.