To e-, or not to e-, the question for the exotic 'Si-III' phase of silicon

April 04, 2017

Washington, DC--It would be difficult to overestimate the importance of silicon when it comes to computing, solar energy, and other technological applications. (Not to mention the fact that it makes up an awful lot of the Earth's crust.) Yet there is still so much to learn about how to harness the capabilities of element number fourteen.

The most-common form of silicon crystallizes in the same structure as diamond. But other forms can be created using different processing techniques. New work led by Carnegie's Tim Strobel and published in Physical Review Letters shows that one form of silicon, called Si-III (or sometimes BC8), which is synthesized using a high-pressure process, is what's called a narrow band gap semiconductor.

What does this mean and why does it matter?

Metals are compounds that are capable of conducting the flow of electrons that makes up an electric current, and insulators are compounds that conduct no current at all. Semiconductors, which are used extensively in electronic circuitry, can have their electrical conductivity turned on and off--an obviously useful capability. This ability to switch conductivity is possible because some of their electrons can move from lower-energy insulating states to higher-energy conducting states when subjected to an input of energy. The energy required to initiate this leap is called a band gap.

The diamond-like form of silicon is a semiconductor and other known forms are metals, but the true properties of Si-III remained unknown until now. Previous experimental and theoretical research suggested that Si-III was a poorly conducting metal without a band gap, but no research team had been able to produce a pure and large enough sample to be sure.

By synthesizing pure, bulk samples of Si-III, Strobel and his team were able to determine that Si-III is actually a semiconductor with an extremely narrow band gap, narrower than the band gap of diamond-like silicon crystals, which is the most-commonly utilized kind. This means that Si-III could have uses beyond the already full slate of applications for which silicon is currently used. With the availability of pure samples, the team was able to fully characterize the electronic, optical, and thermal transport properties of Si-III for the first time.

"Historically, the correct recognition of germanium as a semiconductor instead of the metal it was once widely believed to be truly helped to start the modern semiconductor era; similarly, the discovery of semiconducting properties of Si-III might lead to unpredictable technological advancement," remarked lead author, Carnegie's Haidong Zhang. "For example, the optical properties of Si-III in the infrared region are particularly interesting for future plasmonic applications."
-end-
Other co-authors on the paper are Hanyu Liu, Zhenxian Liu, and Michael Guerette of Carnegie; Kaya Wei and George Nolas of University of South Florida; Oleksandr Kurakevych and Yann Le Godec of Institut de Minéralogie de Physique des Matériaux et de Cosmochimie; and Joshua Martin of the National Institutes of Standards and Technology.

Caption: Is Si-III a metal with freely travelling electrons, or a semiconductor with a discrete energy gap that can 'stop' the flow? It turns out the latter is true, but the band gap of Si-III is so small that electrons can 'proceed with caution' through the structure. Illustration is courtesy of Tim Strobel.

This work was supported as part of the Energy Frontier Research in Extreme Environments (EFRee) Center, and Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

Related Semiconductor Articles from Brightsurf:

Blue phosphorus: How a semiconductor becomes a metal
Blue phosphorus, an atomically thin synthetic semiconductor, becomes metallic as soon as it is converted into a double layer.

A new method to measure optical absorption in semiconductor crystals
Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy - a method for probing semiconducting crystals with light to detect defects and impurities.

Medical robotic hand? Rubbery semiconductor makes it possible
A medical robotic hand could allow doctors to more accurately diagnose and treat people from halfway around the world, but currently available technologies aren't good enough to match the in-person experience.

Laser allows solid-state refrigeration of a semiconductor material
A team from the University of Washington used an infrared laser to cool a solid semiconductor by at least 20 degrees C, or 36 F, below room temperature, as they report in a paper published June 23 in Nature Communications.

Scientists create smallest semiconductor laser
An international team of researchers announced the development of the world's most compact semiconductor laser that works in the visible range at room temperature.

Clemson researcher's novel MOF is potential next-gen semiconductor
Clemson professor Sourav Saha demonstrated a novel double-helical metal organic framework architecture in a partially oxidized form that conducts electricity, potentially making it a next-generation semiconductor.

A gold butterfly can make its own semiconductor skin
A nanoscale gold butterfly provides a more precise route for growing/synthesizing nanosized semiconductors that can be used in nano-lasers and other applications.

Scientists pioneer new generation of semiconductor neutron detector
In a new study, scientists have developed a new type of semiconductor neutron detector that boosts detection rates by reducing the number of steps involved in neutron capture and transduction.

Scientists see defects in potential new semiconductor
A research team has reported seeing, for the first time, atomic scale defects that dictate the properties of a new and powerful semiconductor.

Bending an organic semiconductor can boost electrical flow
Slightly bending semiconductors made of organic materials can roughly double the speed of electricity flowing through them and could benefit next-generation electronics such as sensors and solar cells, according to Rutgers-led research.

Read More: Semiconductor News and Semiconductor Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.