Scanning tunneling microscopy of quantum confinement effects in lead sulfide thin films

We report the use of the scanning tunneling spectroscopy (STS) to investigate 1-dimensional quantum confinement effects in lead sulfide (PbS) thin films. The band gap was varied by control of the PbS film thickness and barrier materials. PbS quantum well structures with a thickness range of 1-20 nm were prepared by atomic layer deposition (ALD) due to its unique characteristics: precise thickness control with sub-nm resolution, pinhole-free films, and conformal coating. Two barrier materials were selected based on their barrier height: silicon dioxide as a high barrier material and zinc sulfide as a low barrier material. PbS quantum wells embedded in different barrier materials were characterized with STS to measure band gap variations. Experimental results showed that the band gap of PbS thin films increased as film thickness decreased and barrier height increased. The experimental results showed good agreement with an effective mass model.