Low temperature synthesis of α- and β-phase Bi2O3 thin film via B doping: tailoring optical band gap and n- to p-type Bi2O3

In this article, we fabricated p-type bismuth oxide (Bi2O3) thin films with tailoring optical band gap by boron (B) doping, for the first time. In addition, an effort is made to see the influence of B doping on the surface morphological, structural, optical and electrical transport properties of Bi2O3 thin films. Field Emission Scanning Electron Microscope (FESEM) images demonstrated that the film surface is covered by well-defined multigonal shaped particles and glassy surface. alpha-Bi2O3 (monoclinic) and beta-Bi2O3 (tetragonal) phase structures are confirmed by X-ray diffraction (XRD) analysis. The average crystallite size is decreased from 46.62 to 23.57 nm with B doping concentration. Moreover, the average strain, stress and dislocation density values are calculated using XRD data. The optical band gaps have changed from 3.70 to 3.99 eV with the texture coefficient values of (11 (2) over bar) orientation plane. A minimum refractive index and optical conductivity value are found to be 2.58 and 2.23 x 10(6) ohm(-1) m(-1) for 3 at.% B content. Electrical parameters, viz. resistivity, sheet resistance, charge carrier concentration, mobility and conductivity types are investigated using a van der Pauw Hall measurement system. Electrical measurements demonstrated that the resistivity values are found to vary in the range of 1.23-1.82, x 10(3) omega-m with increasing B doping concentrations. A high-quality factor is obtained 5.52 x 10(-6) ohm(-1) for higher doping content at 550 nm wavelength. This work promotes a new vision into the fabrication of p-type Bi2O3 thin films and facilitates their application in the field of optoelectronic devices, viz. window layer coating, p-n junction and photovoltaic applications.