A DATE type always includes the date component.
One option is to continue using DATE and write your code to ignore the date component. In order to make queries on the time efficient, you might want to create a function-based index on something like TO_CHAR( date_field, 'HH24:MI:SS' ) and use that expression in your queries.
Alternatively, you could use a NUMBER field to store the number of seconds since midnight, and write your queries in terms of that.
