Probing Quantum Phenomena in Tiny Transistors

Estimated reading time: 4 minutes

Nearly 1,000 times thinner than a human hair, nanowires can only be understood with quantum mechanics. Using quantum models, physicists from Michigan Technological University have figured out what drives the efficiency of a silicon-germanium (Si-Ge) core-shell nanowire transistor.

Core-Shell Nanowires

The study, published last week in Nano Letters, focuses on the quantum tunneling in a core-shell nanowire structure. Ranjit Pati, a professor of physics at Michigan Tech, led the work along with his graduate students Kamal Dhungana and Meghnath Jaishi.

Core-shell nanowires are like a much smaller version of electrical cable, where the core region of the cable is made up of different material than the shell region. In this case, the core is made from silicon and the shell is made from germanium.  Both silicon and germanium are semiconducting materials. Being so thin, these semiconducting core-shell nanowires are considered one-dimensional materials that display unique physical properties.

The arrangements of atoms in these nanowires determine how the electrons traverse through them, Pati explains, adding that a more comprehensive understanding of the physics that drive these nanoscale transistors could lead to increased efficiency in electronic devices.

"The performance of a heterogeneous silicon-germanium nanowire transistor is much better than a homogeneous silicon nanowire," Pati says. "In our study, we've unraveled the quantum phenomena responsible for its superior performance."

Field Effect Transistors

Transistors power our digital world. And they used to be large—or at least large enough for people to see. With advances in nanotechnology and materials science, researchers have been able to minimize the size and maximize the numbers of transistors that can be assembled on a microchip.

The particular transistor that Pati has been working on is a field effect transistor (FET) made out of core-shell nanowires. It manipulates the electrical current in the nanowire channel using a gate bias. Simply put, a gate bias affects electric current in the channel like a valve controls water flow in a pipe. The gate bias produces an electrostatic field effect that induces a switching behavior in the channel current. Controlling this field can turn the device on or off, much like a light switch.

A field effect transistor (FET) uses a gate bias to control electrical current in a channel between a source and drain, which produces an electrostatic field around the channel.

Several groups have successfully fabricated core-shell nanowire FETs and demonstrated their effectiveness over the transistors currently used in microprocessors. What Pati and his team looked at is the quantum physics driving their superior performance.

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