# Detection of a single-charge defect in a metal-oxide-semiconductor structure using vertically coupled Al and Si single-electron transistors

## TL;DR

This paper demonstrates the detection of a single-charge defect at the Si/SiO_2 interface using vertically coupled Al and Si single-electron transistors, providing insights into interface trap characteristics.

## Contribution

It introduces a novel method employing vertically coupled SETs to detect and analyze a single-charge defect at the semiconductor interface.

## Key findings

- Detected a single-charge defect tunnel-coupled to a Si SET.
- Estimated the defect size to be less than 1 nm radius.
- Located the defect approximately 20 nm from the Si SET.

## Abstract

An Al-AlO_x-Al single-electron transistor (SET) acting as the gate of a narrow (~ 100 nm) metal-oxide-semiconductor field-effect transistor (MOSFET) can induce a vertically aligned Si SET at the Si/SiO_2 interface near the MOSFET channel conductance threshold. By using such a vertically coupled Al and Si SET system, we have detected a single-charge defect which is tunnel-coupled to the Si SET. By solving a simple electrostatic model, the fractions of each coupling capacitance associated with the defect are extracted. The results reveal that the defect is not a large puddle or metal island, but its size is rather small, corresponding to a sphere with a radius less than 1 nm. The small size of the defect suggests it is most likely a single-charge trap at the Si/SiO_2 interface. Based on the ratios of the coupling capacitances, the interface trap is estimated to be about 20 nm away from the Si SET.