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

Although beta-Ga2O3 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 beta-Ga2O3 nanowires by the vapor-liquid-solid (VLS) approach. Sn-doped beta-Ga2O3 NWs with diameters of 100-250 nm retained the monoclinic beta-Ga2O3 structure, though photoluminescence (PL) emission was red-shifted by up to 50 nm relative to the deep defect band typically observed for pure beta-Ga2O3 NWs. When higher amounts of Sri were introduced, individual Ga2O3-SnO2 heterostructures (HS) self-assembled, to form three distinctive parts: monocrystalline Sn-doped beta-Ga2O3, poorly crystalline Sn-doped beta-Ga2O3, and polycrystalline Ga-doped SnO2, thus realizing a p-n junction within a single HS. Factors responsible for the self-assembly of Ga2O3-SnO2 HS are the different vapor pressures of Sri and Ga and different growth kinetics of Ga2O3 and SnO2. 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 rim, Sn-doped Ga2O3 sections of the HS exhibited the rarely observed orthorhombic epsilon-Ga2O3 phase.