PHP Inserting variable inside EOT

I want to insert a variable inside the EOT but is not working (I am new to php, maybe that's why). This code is part of a script, when I echo $username alone it shows the real name, but when I put it inside EOT is displaying plain text not the real name..

What am I doing wrong?

$username=getUsername($ID);

echo <<<'EOT'

Some HTML code goes here

Hello $username, welcome back!

Some HTML code goes here

EOT;