Atomic Layer Deposition of Lead Sulfide Thin Films for Quantum Confinement

Lead sulfide (PbS) thin films were deposited by atomic layer deposition (ALD) for the fabrication of quantum well structures. A linear growth rate of 0.9 Å/cycle and pulse saturation behavior characteristic of ALD were observed. The stoichiometry of the films was confirmed using X-ray photoelectron spectroscopy (XPS) with no chemical contamination. The polycrystalline film morphology was observed with grain sizes ranging from 30 to 150 nm. Size quantization effects are shown on the bandgap by fabricating PbS quantum wells with a sub-10 nm thickness. Bandgap values were measured by tunneling spectroscopy (TS) using scanning tunneling microscopy (STM) and are matched to an effective mass model. The bandgap of the films was changed from 0.4 to 2.75 eV by varying only the number of ALD cycles.