Colloidal Synthesis of P-Type Zn₃As₂ Nanocrystals

Zinc pnictides (Zn₃Pn₂, where Pn represents P, As, or Sb) are compound II–V semiconductors composed of earth-abundant elements belonging to the II and V groups of the periodic table. These materials exhibit exceptional properties, such as high carrier mobility, low effective mass of charge carriers, anisotropic charge transport characteristics, and narrow band gaps. Notably, Zn₃As₂, which has a band gap of approximately 1.0 eV, has significant potential for optoelectronic applications across a wide range of wavelengths. Given the substantial advantages and opportunities associated with intrinsically p-type nanomaterials, particularly considering the abundance of well-established inorganic n-type nanomaterials, Zn₃As₂ is a highly promising material owing to its inherent p-type characteristics and appropriate bandgap.<br/>Colloidal synthesis of nanocrystals (NCs) from compound semiconductors offers precise control over their size, resulting in a wide range of tunable electrical and optical properties. These colloidal NCs, such as Zn₃As₂ NCs, exhibit characteristics that make them highly suitable for low-cost large-area processing, opening up diverse applications in fields such as solar energy harvesting and photodetection spanning the visible to infrared regions. However, despite the outstanding properties of colloidal Zn₃As₂ nanocrystals, research in this area is lacking because of the absence of suitable precursors, the occurrence of surface oxidation, and the intricacy of the crystal structures. Zn precursors such as diethylzinc, or As precursors such as tris(trimethylsilyl)arsane exhibit high reactivity but yield Zn₃As₂ NCs that are too small. Also, previously reported Zn₃As₂ NCs have exhibited low crystallinity, which was primarily attributed to the difficulty in achieving precise stoichiometry during their formation.<br/>In this study, a novel and facile solution-based synthetic approach is presented for obtaining highly crystalline p-type Zn₃As₂ nanocrystals with accurate stoichiometry. By carefully controlling the feed ratio and reaction temperature, colloidal Zn₃As₂ nanocrystals are successfully obtained. Moreover, the mechanism underlying the conversion of As precursors in the initial phases of Zn₃As₂ synthesis is elucidated. Furthermore, these nanocrystals have been employed as active layers in field-effect transistors that exhibit inherent p-type characteristics with native surface ligands. To enhance the charge transport properties, a dual passivation strategy is introduced via phase-transfer ligand exchange, leading to enhanced hole mobilities as high as 0.089 cm² V^–1 s^–1. This study not only contributes to the advancement of nanocrystal synthesis, but also opens up new possibilities for previously underexplored p-type nanocrystal research.