Local laser-induced solid-phase recrystallization of phosphorus-implanted Si/SiGe heterostructures for contacts below 4.2 K

TL;DR

This paper introduces a laser-based local annealing technique for creating ohmic contacts in Si/SiGe heterostructures, enabling high-quality contacts at cryogenic temperatures while preserving the delicate layer structure.

Contribution

It presents a novel laser annealing process for ion-implanted contacts in Si/SiGe heterostructures, reducing thermal impact and enabling optimized low-temperature device performance.

Findings

Laser annealing achieves comparable or better contact quality than global annealing.

The process is quickly adaptable using optical inspection calibration.

High electron mobility and low contact resistance are maintained below 4.2 K.

Abstract

Si/SiGe heterostructures are of high interest for high mobility transistor and qubit applications, specifically for operations below 4.2 K. In order to optimize parameters such as charge mobility, built-in strain, electrostatic disorder, charge noise and valley splitting, these heterostructures require Ge concentration profiles close to mono-layer precision. Ohmic contacts to undoped heterostructures are usually facilitated by a global annealing step activating implanted dopants, but compromising the carefully engineered layer stack due to atom diffusion and strain relaxation in the active device region. We demonstrate a local laser-based annealing process for recrystallization of ion-implanted contacts in SiGe, greatly reducing the thermal load on the active device area. To quickly adapt this process to the constantly evolving heterostructures, we deploy a calibration procedure based exclusively on optical inspection at room-temperature. We measure the electron mobility and contact resistance of laser annealed Hall bars at temperatures below 4.2 K and obtain values similar or superior than that of a globally annealed reference samples. This highlights the usefulness of laser-based annealing to take full advantage of high-performance Si/SiGe heterostructures.