Researchers unveil rare electron localization phenomenon in semiconductors

The JNCASR team, led by Associate Professor Bivas Saha, successfully demonstrated this transition using oxygen and magnesium as random dopants in a single-crystalline scandium nitride semiconductor.

A team of researchers at Bengaluru’s Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) has unveiled a rare electron localization phenomenon known as the quasiclassical Anderson transition, which holds significant potential for enhancing semiconductor performance and expanding their applications in areas such as lasers, optical modulators, and photoconductors.

Anderson Localization, a concept introduced by American theoretical physicist P. W. Anderson, describes the absence of conduction in metals or semiconductors due to doping and impurities, leading to a metal-insulator transition. Traditionally, this phenomenon was associated with geometric or topological defects in lattices. However, theoretical physicists Boris I. Shklovskii and Alex L. Efros proposed that random distributions of charged dopants could also induce a similar transition, known as the quasiclassical Anderson transition. Despite extensive theoretical interest, direct experimental evidence of this transition has been elusive—until now.

The JNCASR team, led by Associate Professor Bivas Saha, successfully demonstrated this transition using oxygen and magnesium as random dopants in a single-crystalline scandium nitride semiconductor. Their findings, published in Physical Review B, revealed that the introduction of these dopants creates fluctuations in electrical potential, leading to a profound band structural change in the material. This results in a percolative metal-insulator transition, where the material's structure remains unchanged, but its electronic properties shift dramatically.

This transition is marked by a staggering nine orders of magnitude change in resistivity, offering new insights into electron localization behavior. The researchers employed a unique approach, utilizing a magnesium-compensated scandium nitride semiconductor and depositing it under ultrahigh vacuum growth conditions. The resulting potential fluctuations not only triggered the metal-insulator transition but also caused anomalous behaviors in carrier mobility, thermopower, and photoconductivity.

Dr. Dheemahi, the lead author, emphasized the potential applications of these findings, stating, “This electronic transition in single-crystalline and epitaxial semiconductors could lead to breakthroughs in various technologies, including lasers, optical modulators, photoconductors, spintronic devices, and photorefractive dynamic holographic media.” The ability to manipulate semiconducting properties through potential fluctuations may pave the way for more efficient semiconductor technologies.

Professor Bivas Saha highlighted the significance of this research, noting, “Our work marks the first experimental confirmation of the quasiclassical Anderson transition and percolative metal-insulator transition in materials. We have demonstrated how random dopant distributions drastically alter electron transport in semiconductors, invoking the percolation process. This phenomenon, akin to the Anderson transition, could revolutionize our understanding of electron localization in materials.”

This collaborative research also involved contributions from the University of Sydney, Australia, and Deutsches Elektronen-Synchrotron in Germany, underscoring its global impact on the field of semiconductor physics.