Growth of Sn-Doped β-Ga₂O₃ Nanowires and Ga₂O₃−SnO₂ Heterostructures for Gas Sensing Applications

Although β-Ga 2 O 3 thin films and nanowires (NWs) show promise as very stable and reliable active components for high temperature gas sensors, their use at room temperatures is limited due to poor electrical conductivity. To address this problem, we grew Sn-doped β-Ga 2 O 3 nanowires by the vapor−liquid−solid (VLS) approach. Sn-doped β-Ga 2 O 3 NWs with diameters of 100−250 nm retained the monoclinic β-Ga 2 O 3 structure, though photoluminescence (PL) emission was red-shifted by up to 50 nm relative to the deep defect band typically observed for pure β-Ga 2 O 3 NWs. When higher amounts of Sn were introduced, individual Ga 2 O 3 −SnO 2 heterostructures (HS) self-assembled, to form three distinctive parts: monocrystalline Sn-doped β-Ga 2 O 3, poorly crystalline Sn-doped β-Ga 2 O 3, and polycrystalline Ga-doped SnO 2, thus realizing a p-n junction within a single HS. Factors responsible for the self-assembly of Ga 2 O 3 −SnO 2 HS are the different vapor pressures of Sn and Ga and different growth kinetics of Ga 2 O 3 and SnO 2 . Inhomogeneity in chemical content and structural composition correlated with distinct optical properties along the length of single HS. When diameters of these HS were less than 100 nm, Sn-doped Ga 2 O 3 sections of the HS exhibited the rarely observed orthorhombic ε-Ga 2 O 3 phase.