Include php file by Ajax when click Tabs

I want to include 1 php file in “inc” folder in my WORDPRESS theme by ajax.
By the way i get the ID of “li a” when click per tab.
Please tell me what wrong in my code. I’m not good in javascript.
Thanks for help.

Here my JS code.

<script type="text/javascript">
jQuery(".tab_menu ul li a").click(function() {
    jQuery("#result").html("<span class='loading'>Loading...</span>").fadeIn();
        var $linkId = $(".tab_menu ul li a").attr("id");
        $.ajax({
          url: "<?php echo get_bloginfo('template_url').'/inc/';?>" +$linkId+ ".php",
          type: "POST",
          data: {tab: linkId},
          success: function(msg){
            jQuery(".loading").remove();
            jQuery("<div>").html(msg).appendTo("div#result").hide().fadeIn("slow");
        }
    });
    return false;
});
</script>

And here my tabs menu code:

<div class="tab_menu">
            <ul>
            <li><a id="">Tab 1</a></li>
            <li><a id="tab_hinh_anh">Tab 2</a></li>
            <li><a id="tab_binh_luan">Tab 3</a></li>
            <li><a id="tab_ban_do">Tab 4</a></li>
            </ul>
            <div class="clear"></div>
</div><!--end tab-menu-->

My php file to include in “inc” folder and file name = linkId +.php (ex: inc/tab_ban_do.php)

When i Click per tab.. it fadeIn the Loading… text.. but not load php file.
And I view source: + linkId + not be change to ID of the tab. 🙁