Trivalent Atom Defect-Complex Induced Defect Levels in Germanium for Enhanced Ge‑Based Device Performance

Defect complexes have a significant impact on the structural, electronic, optical and electrical properties of semiconductors. Several defect complexes formed by n -type and p -type atoms in Ge have been implemented for the development of improved modern microelectronic devices. However, there is no reported study on the substitutional-interstitial defect complexes formed by trivalent atoms in Ge. This paper presents a hybrid density functional theory study of the structural, electronic, formation and defect levels induced by the trivalent substitutional-interstitial (B _Ge B _i , Al _Ge Al _i , Ga _Ge Ga _i and In _Ge In _i ) defect complexes in Ge. The formation energy results showed that the trivalent substitutional-interstitial defect complexes in Ge were formed with relatively low energy. Ga _Ge Ga _i under equilibrium conditions is the most energetically favourable, with a formation energy of 3.95 eV. All trivalent atoms are bound with their respective substitutional and interstitial atoms without dissociation. With respect to their ability to form as a defect cluster, the In _Ge In _i is the most stable defect complex, with a binding energy of 2.91 eV. Except for the Ga _Ge Ga _i , all studied defect complexes are electrically active. The B _Ge B _i and Al _Ge Al _i induced a single acceptor level, while the In _Ge In _i induced active donor levels. The acceptor defect level induced by the B _Ge B _i is deep, and that of the Al _Ge Al _i is shallow, close to the conduction band. The results of this study are important, as they provide theoretical insights into the experimental characterization of the substitutional-interstitial defect complexes formed by trivalent impurities in germanium, which could help to improve Ge-based microelectronic devices.