Synthesis and Material Properties of Bi2Se3 Nanostructures Deposited by SILAR

Bi2Se3 was synthesized by a room-temperature deposition technique and successive ionic layer adsorption and reaction (SILAR) method with the aim to understand the formation, crystallinity, optical properties, and energy band structure of this material. The Bi2Se3 morphology was found to change from nanoparticles to that of a nanocluster network by increasing the SILAR deposition cycles. The crystalline structure of as-prepared Bi2Se3 determined from the grazing incidence X-ray diffraction (GI-XRD) pattern was found to have a mixed of metastable orthorhombic and rhombohedral phases which was further confirmed from our analysis of the Raman spectra. The optical bandgap of Bi2Se3 varied from 1.58 to 1.05 eV for 15-90 cycles of deposition, in contrast to the semimetallic 0,3 eV bandgap exhibited by the pure rhombohedral phase. A schematic band diagram of Bi2Se3 prepared by 45 SILAR cycles was constructed for the mixed-phase Bi2Se3. The flat-band potential was determined to be at 0.46 V vs. RHE from Mott-Schottky analysis. Low-temperature annealing at 100 degrees C for 1 h resulted in the improvement of the rhombohedral phase fraction which was confirmed from analysis of GI-XRD pattern and pronounced Egg and A(1g)(2) bulk vibrational modes in the Raman spectrum. The absorption cutoff after annealing was found to be red-shifted combined with a sub-bandgap absorption above 0.78 eV. The post-annealing results indicated the onset of an early stage transition from semiconductor to semi-metallic properties for Bi2Se3 .