When you simulate a new device, you can have the freedom to choose to simulate an heterostructure. Even if in this actual version of GNU Archimedes the heterostructures are not taken into account, the user have to specify that the semiconductor device simulated is made of Silicon, Gallium Arsenide or Germanium. This is done in order to prepare the next versions of GNU Archimedes. So, at the moment, the only two correct uses of the command MATERIAL are the following
MATERIAL SILICON MATERIAL GAAS MATERIAL GERMANIUM