If you're looking for critical information on a particular author, or want to read about several in order to compare and choose, the Dictionary of Literary Biography (DLB) can be an invaluable guide.You'll find the entire DLB in the Loker Reading Room on the second floor of Widener Library (call number RR3129.5).
Contemporary German Fiction Writers, First Series and Second Series. (Volume 69 / Volume 75) In these two volumes of the DLB, you'll find overviews of the lives, careers, and critical reception of 82 German writers who became prominent from 1945 to 1975.
Twentieth Century German Dramatists. (Volume 124) Fifty entries on German playwrights from 1919 through 1992.
The Babel Guide to German Fiction in English Translation -- Lists and reviews all translations published since 1950.
For critical studies of German literature, use the Advanced Search in HOLLIS "Library Catalog" mode, and search for the Subject German fiction 20th century criticism (see screenshot). Limit the language to English, if necessary.