Growth Mode-Dependent Bi Incorporation and Carrier Localization in GaAsBi Wires

Dilute bismide III-V semiconductors are attractive for infrared optoelectronics because of their large band gap bowing and suppressed Auger recombination; however, achieving controlled Bi incorporation with uniform optical quality remains challenging. Here, we systematically investigate the relationship between growth mode, Bi incorporation, and carrier dynamics in GaAsBi wires grown by molecular beam epitaxy. By varying the substrate temperature and V/III beam-equivalent pressure ratio, growth transitions from planar deposition to vapor-liquid-solid (VLS) wire growth and subsequently to vapor-solid (VS) growth, defining a process window for homogeneous axial Bi incorporation of up to 2.4%. STEM-EDS analysis confirms uniform axial composition under stable VLS conditions, whereas VS growth results in radial overgrowth and compositional averaging. Temperature-dependent photoluminescence reveals growth-dependent alloy fluctuations and carrier localization, which are quantitatively analyzed using a two-activation Arrhenius model to distinguish carrier delocalization from nonradiative recombination pathways. Homogeneous GaAsBi wires exhibit an internal quantum efficiency of ∼0.2% at 260 K and a temperature-dependent band gap shift slightly larger than those of GaAs nanowires and GaAsBi bulk alloys. Furthermore, droplet-mediated growth enables axial GaAsBi/GaAs heterostructures, demonstrating controlled band-structure engineering in dilute bismide wires. This work establishes a quantitative growth-mode stability window for homogeneous axial Bi incorporation in GaAsBi wires and reveals how VLS-to-VS transitions fundamentally alter carrier localization and thermal quenching behavior.