Android market publishing setting in unity free

Dear Friends,

I installed unity latest version available with free license. After creating the demo apk file while checking apk compatibility with play store its only producing the apk in debug mode. I tried android publishing setting in player setting but it is showing Key->Alias as "unsigned (Debug)" only. There is no other option to choose from. Kindly confirm if it is not possible to publish without paid android license of some other setting is needed.

Kind Regards Rajender Bhambhu