The present disclosure provides a semiconductor device structure in accordance with some embodiments. In some embodiments, the semiconductor device structure includes a semiconductor substrate of a first semiconductor material and having first recesses. The semiconductor device structure further includes a first gate stack formed on the semiconductor substrate and being adjacent the first recesses. In some examples, a passivation material layer of a second semiconductor material is formed in the first recesses. In some embodiments, first source and drain (S/D) features of a third semiconductor material are formed in the first recesses and are separated from the semiconductor substrate by the passivation material layer. In some cases, the passivation material layer is free of chlorine.