Thermal activation of low-density Ga implanted in Ge

TL;DR

This study investigates the optimal thermal annealing conditions for activating low-density Ga ions implanted in Ge, aiming to facilitate their use as nuclear spin qubits in solid-state quantum computing.

Contribution

It extends activation studies of Ga in Ge into the low-density regime and identifies optimal annealing temperatures and fluences for potential quantum computing applications.

Findings

Maximum activation of 64% at 650°C for high fluence

Activation increases monotonically with implant fluence

Optimal annealing temperature range is 400-650°C

Abstract

The nuclear spins of low-density implanted Ga atoms in Ge are interesting candidates for solid state-based qubits. To date, activation studies of implanted Ga in Ge have focused on high densities. Here we extend activation studies into the low-density regime. We use spreading resistance profiling and secondary ion mass spectrometry to derive electrical activation of Ga ions implanted into Ge as a function of rapid thermal anneal temperature and implant density. We show that for our implant conditions the activation is best for anneal temperatures between 400 and 650 $^\circ$C, with a maximum activation of 64% at the highest fluence. Below 400 $^\circ$C, remaining implant damage results in defects that act as superfluous carriers, and above 650 $^\circ$C, surface roughening and loss of Ga ions are observed. The activation increased monotonically from 10% to 64% as the implant fluence increased from $6\times10^{10}$ to $6\times10^{12}$ cm$^{-2}$. The results provide thermal anneal conditions to be used for initial studies of using low-density Ga atoms in Ge as nuclear spin qubits.