Deposition and characterization of cadmium sulfide (CdS) by chemical bath deposition using an alternative chemistry cadmium precursor

• Deposition of CdS by a new chemistry.
• New CdS chemistry shows better film uniformity.
• New Cds chemistry with wide processing window.
• Ability to deposit very thin CdS layer.

A uniform ultrathin (<30 nm) CdS buffer layer was deposited by CBD by utilizing an alternative bath based on N-methylthiourea and was compared with the standard sulfur source. The CdS deposited by this new bath formulation was deposited separately on soda lime glass (SLG), sputtered molybdenum/glass and co-evaporated copper indium gallium di-selenide (CIGS)/Mo/glass substrates. The CdS film properties were investigated by scanning electric microscope (SEM), X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), UV–vis spectroscopy, and quantum efficiency (QE). The films deposited with N-methylthiourea were found to have a similar granular structure, deposit in the same stoichiometry, and have similar device performance as the standard when deposited in the 60–80 nm film thickness range. When the CdS layer was deposited ultrathin in the 20–30 nm range, it was found to have good surface coverage with no evidence pinholes or device shunting. QE data indicated 40 nm thick CdS samples deposited using Thiourea as a sulfur source demonstrated better overall results however depositing a 20 nm thick CdS demonstrated N-methylthiourea as a sulfur source could deposit with good quantum efficiency and more consistently. Devices fabricated with ultrathin CdS using N-metyhlthiourea showed better device performance compared with devices fabricated using the standard CdS chemistry.