TDPAC and first-principles study of electronic and structural properties of Pd-vacancy complex in undoped germanium

TL;DR

This study combines TDPAC experiments and first-principles calculations to investigate the structure and stability of Pd-vacancy complexes in undoped germanium, revealing their configurations, dissociation energy, and behavior upon annealing.

Contribution

It provides the first combined experimental and theoretical analysis of Pd-vacancy complexes in germanium, identifying their structure and energetic properties.

Findings

Pd-vacancy complex aligned along <111> with 8.4(5) Mrad/s frequency

Maximum complex fraction of 76(4)% at 350°C annealing

Dissociation energy of 1.94(5) eV for the complex

Abstract

Pd is one of the metals suitable for inducing low-temperature crystallization in Ge. However, it is not clear how residual Pd atoms are integrated into the Ge lattice. Therefore, time-differential perturbed angular correlations (TDPAC) technique using the 100Pd(100Rh) nuclear probe produced by recoil implantation has been applied to study the hyperfine interactions of this probe in single-crystalline undoped Ge. A Pd-vacancy complex aligned along the <111> crystallographic direction with a unique interaction frequency of 8.4(5) Mrad/s has been identified. This complex was measured to have a maximum relative fraction of about 76(4)% following annealing at 350 oC. Further annealing at higher temperatures reduced this fraction, possibly via dissociation of the complex. Calculations suggest dissociation energy of 1.94(5) eV for the complex. DFT calculations performed in this work are in reasonable good agreement with the experimental values for the electric-field gradient of the defect complex in Ge. The calculations predict a split-vacancy configuration with the Pd on a bond-centred interstitial site having a nearest-neighbour semi-vacancy on both sides (V-PdBI-V).