Exporting unicode characters to Excel in ASP.NET

Response.Clear();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", "attachment;filename=Export.xls");
            Response.ContentType = "application/octet-stream";
            Response.ContentEncoding = System.Text.Encoding.Unicode;
           Response.BinaryWrite(System.Text.Encoding.Unicode.GetPreamble());
            byte[] bytes = System.Text.Encoding.Unicode.GetBytes("ส่วนของโค้ด โปรแกรมที่ใช้ประมวลผล ภาษา");              Response.BinaryWrite(bytes);
            Response.Flush();
            Response.End();