A method of forming a material. The method comprises conducting an ALD layer cycle of a first metal, the ALD layer cycle comprising a reactive first metal precursor and a co-reactive first metal precursor. An ALD layer cycle of a second metal is conducted, the ALD layer cycle comprising a reactive second metal precursor and a co-reactive second metal precursor. An ALD layer cycle of a third metal is conducted, the ALD layer cycle comprising a reactive third metal precursor and a co-reactive third metal precursor. The ALD layer cycles of the first metal, the second metal, and the third metal are repeated to form a material, such as a GeSbTe material, having a desired stoichiometry. Additional methods of forming a material, such as a GeSbTe material, are disclosed, as is a method of forming a semiconductor device structure including a GeSbTe material.