Extra copy of sidebar appears in footer

IF you look at all the templates included in your question, the reason becomes obvious: You’re outputting the sidebar twice.

In index.php you use get_sidebar(), which loads sidebar.php. In that template you’re outputting the widgets:

<aside id="secondary" class="widget-area">
    <?php dynamic_sidebar( 'sidebar-1' ); ?>
</aside><!-- #secondary -->

You’re also using get_footer(), which loads footer.php. In that template you’re also outputting the widgets:

                    <div id="sidebar_widget">
<?php dynamic_sidebar( 'sidebar-1' ); ?>
                    </div>