Effect of heavy Ga doping on defect structure of SnO2 layers



Crystal defects in Ga-doped SnO2 grown on SnO2 buffer layers on r-plane sapphire by plasma-assisted molecular beam epitaxy have been analysed by transmission electron microscopy (TEM). The (101)-oriented epitaxial SnO2 buffer layers contain a high number of crystallographic shear plane (CSP) defects (∼1011 cm−2) and threading dislocations (TDs, ∼1010 cm−2). However, their density reduces with increasing layer thickness. Whereas a Ga atomic concentration of 3.2 × 1016 cm−3 does not lead to any change in the defect structure of the SnO2 layers, heavily doped SnO2 layers ([Ga] ∼ 6.1 × 1020 cm−3) contain a continuous network of coherent Ga-rich precipitates appearing as platelets in crystallographically equivalent SnO2(100) and SnO2(010) planes. Electron conduction through this network might explain the reduced electrical resistivity compared to semi-insulating SnO2 with lower Ga concentration