Get Active Directory User Entry

public static DirectoryEntry GetAdUserEntry(this SPUser user)
{
    try
    {
        var path = "LDAP://DC=[domain name without .com],DC=Corp,DC=net";

        if (!string.IsNullOrEmpty(user.LoginName))
        {
            var userId = user.LoginName.ToUpper().Replace("[ntdomain name]\\", "");
            string filter = string.Format("(&(ObjectClass={0})(sAMAccountName={1}))", "person", userId);

            var properties = new string[] { "fullname" };
            var searchRoot = new DirectoryEntry(path, "[domain userid]", "[password]");

            var search = new DirectorySearcher(searchRoot);

            search.SearchScope = SearchScope.Subtree;
            search.ReferralChasing = ReferralChasingOption.All;
            search.PropertiesToLoad.AddRange(properties);
            search.Filter = filter;
            SearchResult result = search.FindOne();

            if (result != null)
            {
                DirectoryEntry directoryEntry = result.GetDirectoryEntry();
                return directoryEntry;
            }
        }
    }
    catch (Exception ex)
    {
        return null;
    }

    return null;
}