Engineering the Morphology and Properties of MoS₂ Films Through Gaseous Precursor-Induced Vacancy Defect Control

The morphology, structure, and composition of CVD-grown molybdenum disulfide (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>MoS</mi><mn>2</mn></msub></semantics></math></inline-formula>) films were investigated under varying precursor vapor pressures. Increasing sulfur vapor pressure transformed the film morphology from well-defined triangular domains to structures dominated by sulfur-terminated zigzag edges. These morphological changes were accompanied by notable variations in both structural and electrical properties. Non-uniform precursor vapor distribution promoted the formation of intrinsic point defects. To elucidate this behavior, a thermodynamic model was developed to link growth parameters to native defect formation. The analysis considered molybdenum and sulfur vacancies in both neutral and charged states, with equilibrium concentrations determined from the corresponding defect formation reactions. Sulfur vapor pressure emerged as the dominant factor controlling defect concentrations. The model validated experimental observations, with films grown under optimum and sulfur-rich conditions, yielding a carrier concentration of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>9.6</mn><mo>×</mo><msup><mn>10</mn><mn>11</mn></msup></mrow></semantics></math></inline-formula> <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>cm</mi><mrow><mo>−</mo><mn>2</mn></mrow></msup></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>7.5</mn><mo>×</mo><msup><mn>10</mn><mn>11</mn></msup></mrow></semantics></math></inline-formula> <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>cm</mi><mrow><mo>−</mo><mn>2</mn></mrow></msup></semantics></math></inline-formula>, respectively. The major difference in the field-effect transistor (FET) performance of devices fabricated under these two conditions was the degradation of the field-effect mobility and the current switching ratio. The degradation observed is attributed to increased carrier scattering at charged vacancy defect sites.