Diamond—the ultimate, unrealized semiconductor

The highly unique properties of diamond—including outstanding thermal conductivity and the ability to withstand exceedingly high voltages—make it a formidable semiconductor with a wide range of possible applications, particularly in power electronics. But while these singular properties have long been recognized, diamond has never successfully been used in this way. After extensive research on the subject in the 1980s and 90s encountered more difficulty than success, the attempt to manipulate diamond for use in electronics was essentially abandoned.

Dr. Jesús del Alamo, however, did not lose sight of diamond’s tremendous potential, and recent breakthroughs lead him to believe that further exploration of the subject may yield important results. In order to put diamond to work, a process called surface transfer doping must be employed to transfer electric charge from the surface of the diamond to that of another material. While water and certain organic molecules had been the most popular surface “acceptors,” their high volatility limited the thermal stability of the structures, rendering diamond essentially unusable in application. Dr. del Alamo believes a recent finding in the lab of Rafi Kalish, professor of physics at Technion in Israel, which identified molybdenum trioxide (MoO3) as a successful—and much more stable—acceptor, may hold the key to fabricating functional diamond transistors that could be applied to electronic applications.

Putting diamond back on the table

Working with diamond in this context poses significant challenges. “The diamond surface has very unusual properties,” Dr. del Alamo explains. “Our intuition from conventional semiconductor technology fails. It is unstable and seemingly capricious as we process the material.” To make matters worse, the expense associated with working with diamond can be prohibitive; even for tiny samples that are used and reused to make transistors, the fees are astronomical. Add to these hurdles the fact that after the significant obstacles faced by research teams in the 80s and 90s, research into diamonds as a semiconductor had fallen out of fashion and diamond had become, as Dr. del Alamo puts it, “basically untouchable from a research point of view.”

Dr. del Alamo realized at once that the unique mission of the Bose Research Grants would serve his project well; the Bose Foundation’s commitment to funding difficult-to-fund projects that were both high-risk and potentially high-reward would provide him an opportunity to explore these questions in depth. “That’s what the Bose Fellows Grant has allowed us to do: go after something that’s risky, and let us take the necessary steps to pursue avenues that may lead to significant results, ” he explains. “This is a visionary model.”

Diamond’s unique properties would make it applicable across electronics

Dr. del Alamo says, “While there is a long road ahead, the proposed study could revolutionize the world of power electronics by providing a path to finally exploit the extraordinary electronic and thermal properties of diamond.” Indeed, the possible applications of this technology—which include power electronics, quantum computing, and sensing, as well as biologically compatible electronics—are vast and wide-ranging. “The beauty of the Bose Grant is that we can continue to try different approaches,” he explains. “We’re not positive where we’ll end up, but we are confident we will learn a great deal along the way.”

Steady progress thanks to patient support

Leveraging the discovery by Dr. Kalish at Technion-Israel Institute of Technology that metal oxides make for ideal surface transfer acceptors in diamond, Dr. del Alamo’s lab has been able to develop and demonstrate unique transistors using these new materials. “His expertise is metal oxides, and our expertise is making transistors,” he says. “Working together, we have been able to gain valuable insights into the mechanisms of surface transfer doping; for example, that adding hydrogen increases the stability of the acceptor. This puts us in a good place to propose new transistor designs that will hopefully take advantage of these capabilities for high-power applications.”

Dr. del Alamo notes that while progress has been steady, it has also been slow. “Diamond is a very difficult material,” he says. “Of all semiconductor systems we have ever worked with, diamond is by far the hardest.” Also, single-crystal diamond substrates are very expensive—another reason why the Bose grant was so important to his work. “The patient, sustained support over three years has allowed us to do a number of fundamental studies, publish papers, and gain recognition in the field. I have also learned that when dealing with new material systems, it is best to collaborate with well-established experts. This understanding has helped me to launch other research initiatives and has reinvigorated my career.”