Changing the conductivity type of ultrasonically sprayed ZnO thin films: comparison of the effects of Li, N, and B dopants

Abstract

ZnO is a material widely used in technological applications. However, the difficulty of preparing p-type ZnO creates a bottleneck for developing ZnO-based devices. In this study, Li, N, and B-doped ZnO thin films were prepared on glass substrates by ultrasonic spray pyrolysis. To determine the conductivity type, the structural, electrical, and optical properties of all samples were investigated. The crystal structure of all ZnO thin films was hexagonal with planes (100), (002), (101), (102), and (110). The B-doped ZnO thin films had small-sized grains similar to pebble stones. The Li dopant increased the defect concentrations, as the B dopant decreased the defect concentrations in the ZnO thin films. The N doping did not change the band gap (3.22 eV), the Li doping decreased the band gap to 3.20 eV and the B doping increased the band gap to 3.28 eV. The electrical conductivity type of the Li and N-doped ZnO thin films was n-type as in the undoped ZnO, while 4–6% B-doped ZnO thin films showed predominantly p-type conductivity due to the B–O complexes and interstitial oxygen defects. Thus, p-type conductivity was found experimentally in B-doped ZnO thin films.