Jung and Upmanyu Develop First Silicon Nanowires that Operate as an Ultrawide-bandgap Semiconductor
The research of mechanical and industrial engineering professors Yung Joon Jung and Moneesh Upmanyu on “Catalyst-free synthesis of sub 5nm silicon nanowire arrays with massive lattice contraction and wide-band gap” has been published in Nature Communications. The researchers developed silicon nanowires that operate as an ultrawide-bandgap (UWBG) semiconductor—a first in the world of silicon, potentially revolutionizing the integration of etched silicon nanowires into UWBG device applications.
- This is the first report of ultra-wide bandgap in silicon. It is a world record in terms of bandgap that can be achieved in silicon. The past two decades of work has been focused on other materials that have enjoyed success (LEDs, laser diodes) but have several challenges and are expensive.
- Silicon is abundant and, therefore, inexpensive, and can be easily processed—which is why this discovery is significant.
- This discovery sets the stage for silicon-based high-power electronic devices.
- The research also sets the stage for silicon-based quantum materials science. The quantum confinement that leads to this set of properties also makes this form of silicon important for next-generation quantum information and computing.
Professor Jung’s team developed the experimental synthesis of the new form of silicon, and Professor Upmanyu’s group is involved in computational investigations on the basis for the startling properties that this material exhibits.
Background and challenges
Innovations in electronic materials and their devices are powered in large part by advances in semiconductors. The performance of these materials depends on their bandgap, a property that is associated with energy difference between the top of the valence band where the electrons are bound to the atoms, and the bottom of the conduction band, which are highways along which electrons rapidly move within the material. Conventional semiconductors such as silicon and germanium, although quite abundant and lower in cost, are on the lower end of bandgap spectrum, and this has limited their use in high-power devices such as LEDs and as materials for quantum information and computing.
This limitation has led to the development of ultrawide-bandgap (UWBG) semiconductors with bandgaps significantly larger than 3.4eV which enjoy clear advantages over their conventional cousins, with potential applications in extreme environment high-power and RF electronics, power conversion, UV optoelectronics, and quantum information. However, there are several challenges in the reliable synthesis of these materials, driving up the cost of their integration expensive.
Silicon remains the most abundant (and therefore relevant) semiconductor, and while its optoelectronic properties can be tuned by engineering quantum confinement effects within low-dimensional nanostructures such as silicon nanowires (SiNWs), its integration within UWBG applications has been challenging due to severe limitations in the extent of its bandgap engineering (< 3.4 eV).
Jung and Upmanyu for the first time have developed silicon nanowires that operate as a ultrawide-bandgap (UWBG) semiconductor. They developed a novel chemical vapor etching (CVE)-based technique for large-scale synthesis of dense, vertically aligned, structurally uniform and oxidation resistant arrays of sub-5nm SiNWs. The diamond cubic nanowires exhibit an optical bandgap of 4.16 eV, a quasi-particle direct bandgap of 4.75 eV, and a large exciton binding energy of 0.59 eV, about 100 times larger than that of bulk silicon. This extraordinary combination of properties is consistent with a UWBG semiconductor, a first in the world of silicon, potentially revolutionizing the integration of etched SiNWs into UWBG device applications. The integrated exploration, together with promising preliminary results paves the way for scalable synthesis of etched SiNWs with controlled size, geometry, strain, surface states and opto-electronic properties for integration within UWBG device applications.
The scientific impact of this study goes beyond the present context. Large-scale dense arrays of these sub-5 nm SiNWs with phonon and electronic confinement have implications as new materials systems and architectures for gas/chemical/bio sensors, quantum information processing, anodes in Li-ion batteries, and solar cells, where quantum confinement and high surface area is desirable. Different etching chemistries can employed to extend the CVE-based synthesis to other semiconductors such as germanium, GaN SiC, and metallic nanowires.
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