Improved optical transmittance of boron doped ZnO thin films by low pressure chemical vapor deposition with pulse boron doping

A pulse doping technique is introduced to obtain boron doped ZnO thin films with high conductivity and improved transmittance. The ZnO thin films were deposited by low pressure chemical vapor deposition and boron was doped into the ZnO thin films by the pulse supply of B₂H₆ gas. The pulse boron doped ZnO thin films exhibited a well textured surface morphology with large pyramid shape grains and a minimum resistivity about 1.0 × 10^-3Ω·cm. These films also had a lower carrier concentration and higher mobility than conventional boron doped ZnO thin film, which has a similar conductivity value. In addition, because of lower carrier concentration and larger surface grains, the pulse boron doped ZnO films exhibited enhanced total transmittance in the near-infrared wavelength range and diffuse transmittance in the overall wavelength range compared to the conventional boron doped ZnO thin film. CIGS solar cells using pulse boron doped ZnO film showed higher efficiency than those using conventional boron doped ZnO film. Based on these results, we suggest a modified low pressure chemical vapor deposition process with pulse boron doping, which is an advantageous technique to deposit doped ZnO thin films with favorable electrical and optical properties for thin film solar cells.