Irradiation induced modification of the superconducting properties of heavily boron doped diamond

TL;DR

This study investigates how high-energy ion irradiation and subsequent annealing affect the superconducting properties of heavily boron-doped diamond, revealing the critical role of charge carrier concentration and defect management.

Contribution

It demonstrates the control of superconductivity in boron-doped diamond through defect engineering within a single sample, unlike previous studies comparing different samples.

Findings

Superconductivity is suppressed when defect-induced compensation reduces hole concentration below threshold.

Vacuum annealing can recover superconductivity by removing compensating defects.

Superconducting properties depend critically on charge carrier concentration rather than boron content alone.

Abstract

Diamond, a wide band-gap semiconductor, can be engineered to exhibit superconductivity when doped heavily with boron. The phenomena has been demonstrated in samples grown by chemical vapour deposition where the boron concentration exceeds the critical concentration for the metal-to-insulator transition of $n_{MIT} \gtrsim 4\times10^{20}/\text{cm}^3$. While the threshold carrier concentration for superconductivity is generally well established in the literature, it is unclear how well correlated higher critical temperatures are with increased boron concentration. Previous studies have generally compared several samples grown under different plasma conditions, or on substrates having different crystallographic orientations, in order to vary the incorporation of boron into the lattice. Here, we present a study of a single sample with unchanging boron concentration, and instead modify the charge carrier concentration by introducing compensating defects via high energy ion irradiation. Superconductivity is completely suppressed when the number of defects is sufficient to compensate the hole concentration to below threshold. Furthermore, we show it is possible to recover the superconductivity by annealing the sample in vacuum to remove the compensating defects.