Example embodiments may provide phase-change material layers and a method of forming a phase-change material layer and devices using the same by generating a plasma including helium and/or argon in a reaction chamber, forming a first material layer on the object by introducing a first source gas including a first material, forming a first composite material layer on the object by introducing a second source gas including a second material into the reaction chamber, forming a third material layer on the first composite material layer by introducing a third source gas including a third material, and forming a second composite material layer on the first composite material layer by introducing a fourth source gas including a fourth material. Example embodiment phase-change material layers including carbon may be more easily and/or quickly formed at lower temperatures under the helium/argon plasma environment by providing the source gases for various feeding times. Example embodiments may also include memory devices using phase-change memory layers.