Create and save excel file using StringBuilder in server folder using asp.net c#

public void Save_stringBuilder()

    {

        StringBuilder sb = new StringBuilder();

        sb.Append("<table border='1' width='800' align='center' style='text-align:center'><tr><td colspan='3' style=' background-color:#000; height:100; color:#fff; font-size:x-large'>Header</td></tr><tr><td height='100' align='center'><img src='C:\\Users\\Krishna\\Desktop\\SaveGridViewAsExcelOnDisk\\a.gif' width='70' height='80'>&nbsp;</td><td>&nbsp;</td><td><img src='C:\\Users\\Krishna\\Desktop\\SaveGridViewAsExcelOnDisk\\b.gif' width='70' height='80'></td></tr><tr><td>&asldkfj;laksjdk fj;k as askdjflajksdf;</td><td>&nbsp;</td><td>&nbsp;</td></tr><tr><td>&nbsp;</td><td>&asdkf;ajsdlkfj asdjfljasd faskldjflkas;</td><td>&nbsp;</td></tr><tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr><tr><td>&asdkjfflkasjd aksdjfl;jalsd skjdflkkjasd fas;</td><td>&nbsp;</td><td>&nbsp;</td></tr><tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr><tr><td>&nbsp;</td><td  height='100' align='center'><img src='C:\\Users\\Krishna\\Desktop\\SaveGridViewAsExcelOnDisk\\b.gif' width='70' height='80' /> </td><td>&nbsp;</td></tr></table>");

        string path = Server.MapPath("~/Files/");

        if (!Directory.Exists(path))  // create folder if not exist

        {

            Directory.CreateDirectory(path);

        }

        using (StringWriter sw = new StringWriter(sb))

        {

            using (HtmlTextWriter hw = new HtmlTextWriter(sw))

            {

                StreamWriter writer = File.AppendText(path + "SavestringBuilder.xls");

                hw.BeginRender();             

                string html = sb.ToString();

                writer.WriteLine(html);// write file on server folder

                writer.Close();

            }

        }

    }