applescript for nested folders

The script below works well for producing a catalog of files in a folder, but it doesn't include the files in any nested folders. How should I modify it to process the contents of nested folders?

set the_string to ""

tell application "Finder"

repeat with this_item in (get every file in the entire contents of (choose folder))

set the_string to the_string & name of this_item & tab & modification date of this_item & tab & size of this_item & tab & kind of this_item & tab & URL of this_item & return

end repeat

set myfile to open for access (choose file name) with write permission

write the_string to myfile

close access myfile

end tell

Thank you for any help.