Cooling of electrons in a silicon inversion layer

Area of Science:

• Condensed Matter Physics
• Materials Science
• Semiconductor Physics

Background:

• Two-dimensional electron systems (2DES) in silicon metal-oxide-semiconductor field-effect transistors (MOSFETs) are crucial for quantum computing and spintronics.
• Understanding electron-phonon coupling is essential for controlling electron temperature and device performance at low temperatures.
• Bulk silicon's electron-phonon coupling mechanisms are well-understood but may differ in confined 2D systems.

Purpose of the Study:

• To experimentally investigate the low-temperature cooling mechanisms of 2D electrons in silicon MOSFETs.
• To determine the dominant heat transfer pathways from electrons to phonons at millikelvin temperatures.
• To explore the impact of cooling on the electronic transport properties, specifically resistivity, of these devices.

Main Methods:

• Fabrication and characterization of long silicon MOSFET devices.
• Experimental measurements of electron temperature and heat transfer rates down to 100 mK.
• Analysis of electron resistivity as a function of temperature and device geometry.

Main Results:

• Electron cooling in silicon MOSFETs is significantly more effective than predicted by bulk silicon electron-phonon coupling models.
• The extracted electron-phonon heat transfer rate exhibits a cubic dependence on electron temperature.
• Evidence suggests piezoelectric coupling, absent in bulk silicon, is the dominant cooling mechanism in this 2D system.
• At 100 mK, electrons beyond ~100 micrometers from contacts are primarily cooled by phonons.
• Some "metallic" resistivity curves transition to insulating behavior below approximately 300 mK.

Conclusions:

• Piezoelectric coupling plays a dominant role in low-temperature electron cooling in 2D silicon systems, differing from bulk behavior.
• Efficient phonon-mediated cooling impacts electron transport, leading to a metal-insulator transition in some devices at sub-Kelvin temperatures.
• These findings are critical for designing and optimizing low-temperature electronic devices, particularly in quantum information applications.