Nobel Laureate Herb Kroemer, 1928-2024

Tuesday, March 12, 2024

A beloved campus colleague and one of the greatest technological visionaries of our time is gone. UC Santa Barbara emeritus professor Herb Kroemer, who earned a Nobel Prize for his seminal work on compound semiconductors, died last Friday, March 8, at the age of 95. (Read a note about Herb from UCSB Chancellor Henry Yang.)

Born August 25, 1928, in Weimar, Germany, Kroemer came to UCSB in 1976, where he held the Donald W. Whittier Chair in Electrical Engineering and joint faculty appointments in the Electrical and Computer Engineering Department (ECE) and the Materials Department. Kroemer received the Nobel Prize in Physics in 2000 in recognition of his work, which included developing semiconductor heterostructures used in high-speed- and opto-electronics that laid the foundation for the modern era of microchips, computers, and information technology.

“It was a privilege to know Professor Kroemer, not only as a world-class physicist and innovator who played a foundational role in transforming UC Santa Barbara into a leader in engineering and materials science, but also as a teacher, colleague, and friend,” said UCSB Chancellor Henry Yang. “He had a wonderful sense of humor and treated everyone with kindness and humanity. Even with his international renown, he could never turn down an invitation to speak to young students, from elementary to high school. It was amazing to see how he connected with and inspired so many young people.

“He once said, ‘From the beginning, I’ve always been interested in things that were several generations ahead of what people could do. Small steps didn’t really interest me. I was interested in big steps.’ Indeed, Professor Kroemer took big steps throughout his life and work. He was truly an inspiration to us all. Professor Kroemer will be dearly missed by our entire UC Santa Barbara family. Our hearts and thoughts go out to his family and to his many friends and colleagues near and far.”

“In India, there is the concept of a guru, someone who is a teacher in the broadest sense, someone who teaches not only curriculum, facts, skills, and information, but morals, ethics, leadership, graciousness, and generosity,” said Umesh Mishra, dean of the UCSB College of Engineering, who was born and raised in India. “We have been fortunate to share time with Herb Kroemer, who embodies that broad ethos of the guru, who taught physics, materials science, and electrical engineering at the highest level, but also life and behavior. There are not many gurus, and we have lost one.”

"Herb was a pioneer in every way for the Materials Department. He made impactful and far-reaching decisions to work on 3-5 semiconductors, and to build UCSB's first MBE lab; both continue as world-leading strengths in the department today,” noted Materials Department chair, Omar Saleh. “Further, he still reaches scores of students through a pair of extraordinarily lucid  textbooks: Thermal Physics and Quantum Mechanics for Engineering. He was unparalleled as a researcher and educator, and will be sorely missed."

“Herb was a giant in the field of semiconductor physics. His Nobel-Prize–winning work on heterostructures testifies to his almost prophetic ability to envision future technologies—which he himself then brought to fruition by his pioneering work in molecular beam epitaxy,” said materials professor Chris Van De Walle. “He also excelled as a teacher, and countless students benefited from his mentorship; many credit their success in science to the passion that Herb instilled in them. I will miss his wit and wisdom, but am truly grateful for all I learned from him.”

Larry Coldren, UCSB emeritus professor in ECE and Materials, worked closely with Kroemer while figuring out how to emit laser light from semiconductor materials.  He recalled, “Herb always liked banter. At the Nobel Prize banquet, I enjoyed listening to him talk with Zhores Alferov (the Russian who shared the 2000 Nobel Prize with Herb). They could never quite agree upon who first came up with the double-heterostructure, the key to making all modern semiconductor lasers work. Of course, ninety percent of the literature properly gives that credit to Herb.”

Professor Kroemer received a PhD in theoretical physics from Georg August University in Göttingen, Germany, in 1952, writing his dissertation on so-called hot-electron effects in the then-new transistor. That research set the stage for a career in research focused on the physics and technology of semiconductors and semiconductor devices. 

Following work in several research laboratories in Germany and the United States, in 1976 Kroemer persuaded the Electrical & Computer Engineering Department at UCSB to direct a substantial portion of its limited resources to expanding the department’s small semiconductor research program, with a particular focus on the emerging field of compound semiconductor technology. Seeing an opportunity for UCSB to become a leading institution in that area, Kroemer himself became the first member of what would soon become one of the world’s preeminent groups dedicated to the physics and technology of compound semiconductors and the many devices they enable. His discoveries provided the basis for numerous technological innovations we now use on a daily basis – from cell phone and satellite communications, to high-speed transistors and solid-state lighting.

“Herb was an inspiration to everyone,” said ECE and Materials professor John Bowers, a world expert on integrated lasers, the Fred Kavli Chair in Nanotechnology, and the director of the UCSB Institute for Energy Efficiency. “He invented the double-heterostructure laser, which earned him a Nobel prize, but also enabled the first commercial semiconductor lasers, which are used worldwide in fiber optic networks and enabled the Internet, transforming the world.”

Beyond that, Bowers added, “Herb went to many seminars and thesis defenses, which petrified the students making the presentations, because Herb was very sharp and insightful and asked difficult questions. But, he was truly a gentleman and a remarkable scholar, and all of us are better scientists because of him.”

COE associate dean, Ram Seshadri, professor of materials and chemistry and director of the UCSB Materials Research Laboratory, recalled Kroemer’s quick mind, even in his later years. “One time, during the course of being interviewed, a faculty candidate pitched an idea that had a deep-seated flaw. Herb, very much a senior citizen at the time, was nevertheless by far the quickest in the room to say, ‘You just violated the second law (of thermodynamics).” 

ECE professor and chair, B. S. Manjunath, recalled Kroemer’s dedication to providing important support wherever it was needed. “His legacy within our department is marked by his remarkable dedication and profound influence,” he said. “His consistent attendance at faculty meetings and his extensive involvement in all aspects of departmental activities — from structuring courses to recruiting faculty — have left an enduring imprint on me. In about 2006, I invited him to address a gathering at one of the PI meetings for our NSF IGERT [Integrative Graduate Education and Research Traineeship], which included UCSB faculty and students. His message was simple: solve problems that interest you, don’t worry about the applications, and be opportunistic!” Herb’s wise counsel, unwavering support for junior faculty, and passionate advocacy for interdisciplinary research not only shaped the department but also had a lasting impact on the college and the campus at large. He set a standard that will inspire generations to come.”

“Professor Herb Kroemer was a great friend and colleague,” said Steven DenBaars, the UCSB Mitsubishi Distinguished Professor of Materials and co-director of the Solid State Lighting and Energy Electronics Center (SLEEC), which Kroemer helped to inspire. “His invention of the heterostructure fundamentally changed electronic devices and now benefits every person on the planet by making possible more-efficient devices, such as cellphones, LED lights, telecommunications, high-speed transistors, and even electric vehicles.”

Nobel laureate and UCSB materials professor Shuji Nakamura, who with DenBaars co-directs the Solid State Lighting and Energy Electronics Center at UCSB, said of Kroemer, "Herb made numerous fundamental, long-lasting contributions. His concept of the heterostructure for optical devices helped me to invent the blue LED and solid-state lighting."

"Herb was a good friend, a great mentor, and an unsurpassable role model," added Mark Rodwell, the Doluca Distinguished Professor of Electrical and Computer Engineering. "His message was think hard, think critically, and don't be too concerned about the immediate utility of the work: new inventions bring new applications. In that, he was thinking, of course, about the semiconductor double heterojunction laser." 

Kroemer loved to work on things that were well ahead of their time. In the mid-1950s, he became the first to point out the great performance advantages that could be gained in various semiconductor devices by incorporating into them what are now called heterostructures. Most notably, in 1963 he proposed the concept of the double-heterostructure laser, the central concept in the field of semiconductor lasers without which that field would simply not exist. 

Those ideas were far ahead of their time, and required the development of modern epitaxial growth technology before they could become mainstream technologies. Upon coming to UCSB, Kroemer turned to experimental work and became one of the early pioneers in molecular beam epitaxy (MBE), concentrating from the outset on applying the technology to untried new materials systems. His work provided a great stimulus toward the development of those technologies, and his Nobel Prize in 2000 can ultimately be traced to those early papers. 

Since the late 1990s, Kroemer had reverted to purely theoretical work, some of which continued earlier work and some in newer research areas, such as electromagnetic wave propagation in photonic crystals and the physics of nanostructures.

In addition to the Nobel Prize, Kroemer received numerous national and international honors and awards, including the 2002 IEEE Medal of Honor "for contributions to high-frequency transistors and hot-electron devices, especially heterostructure devices from heterostructure bipolar transistors to lasers, and their molecular beam epitaxy technology." 

In 2001, he received the Grand Cross of the Order of Merit of the Federal Republic of Germany, the highest award given by the German government. He was a member of both the National Academy of Engineering and the National Academy of Sciences, and a fellow of the American Physical Society and the Institute of Electrical and Electronics Engineers.

A symposium is being planned to honor Professor Kroemer, and the flag outside Cheadle Hall will be lowered to half-staff on Thursday, March 21. 

Herb Kroemer

Herb Kroemer, 1928-2024