Electrical activity of aluminum, boron, and n-type impurities defect-complexes in germanium: Implications for enhanced Ge-based devices

Abstract

Studies on point defects in germanium (Ge) are increasing, primarily because these defects have the potential to modify the electronic and optical properties of Ge, thereby enhancing device applications. While significant progress has been made in defect studies, a comprehensive understanding of defect complexes resulting from interactions between $p$-type (Al or B) and $n$-type atoms (D${}_{\mathrm{Ge}}$X${}_i$ and D${}_i$X${}_{\mathrm{Ge}}$; where D = Al, B, and X = N, P, As, Sb) is still lacking. Therefore density functional theory calculations of electrically active defect levels in Ge that are caused by interactions between $n$-type impurity atoms and Al or B, are presented. For defect-complexes formed by Al and $n$-type atoms, Al and P exhibit the highest formation stability under equilibrium conditions. Conversely, B${}_{\mathrm{Ge}}$P${}_i$ represents the most energetically favorable defect-complex. With the exception of B${}_{\mathrm{Ge}}$N${}_i$, the energetic stability of all defect-complexes suggests that Al and B interstitials form strong bonds with $n$-type substitutional atoms. Electrical behavior analyses of these defects reveal that defect-complexes formed by Al and $n$-type atoms induce deep defect levels. Specifically, Al${}_{\mathrm{Ge}}$N${}_i$ acts as an acceptor, while Al${}_i$As${}_{\mathrm{Ge}}$ behaves as a donor. The defects B${}_{\mathrm{Ge}}$Sb${}_i$, B${}_i$P${}_{\mathrm{Ge}}$, and B${}_i$As${}_{\mathrm{Ge}}$ donate electrons to the conduction band at energy levels within the range of 3 $k_{B}T$. Furthermore, B${}_{\mathrm{Ge}}$Sb${}_i$ induces shallow donor levels, whereas B${}_{\mathrm{Ge}}$P${}_i$ induces acceptor levels. This study opens new research opportunities in the experimental synthesis of defects and offers insights into controlling them, potentially enhancing electronic devices.