Charge dynamics and Kondo effect in single electron traps in field effect transistors

TL;DR

This paper investigates the complex charge and spin behavior of single electron traps in transistors, revealing a hybrid Kondo and mixed valence state influenced by magnetic fields, with implications for understanding trap occupancy anomalies.

Contribution

It introduces a microscopic model combining polaron tunneling and Kondo effects to describe trap dynamics, highlighting the suppression of magnetic field influence due to Kondo screening.

Findings

Identification of a hybrid Kondo-mixed valence state in traps

Demonstration of magnetic field suppression effects on trap occupancy

Explanation of anomalous magnetic dependence observed experimentally

Abstract

We study magneto-electric properties of single electron traps in metal-oxide-semiconductor field effect transistors. Using a microscopic description of the system based on the single-site Anderson-Holstein model, we derive an effective low energy action for the system. The behavior of the system is characterized by simultaneous polaron tunneling (corresponding to the charging and discharging of the trap) and Kondo screening of the trap spin in the singly occupied state. Hence, the obtained state of the system is a hybrid between the Kondo regime, typically associated with single electron occupancy, and the mixed valence regime, associated with large charge fluctuations. In the presence of a strong magnetic field, we demonstrate that the system is equivalent to a two level-level system coupled to an Ohmic bath, with a bias controlled by the applied magnetic field. Due to the Kondo screening, the effect of the magnetic field is significantly suppressed in the singly occupied state. We claim that this suppression can be responsible for the experimentally observed anomalous magnetic field dependence of the average trap occupancy in ${\rm Si-Si0_2}$ field effect transistors.