a silicon - on - insulator device with a strained silicon film has a substrate , and a buried oxide layer on the substrate . silicon islands are formed on the buried oxide layer , the silicon islands being separated from each other by gaps . the buried oxide layers has recesses directly under the gaps . a material fills the recesses and the gaps , this material being different from the material forming the buried oxide layer . the material induces a net amount of strain in the silicon islands , thereby modifying the electrical properties of carriers in the silicon film and improving device performance .