Thank you for you guys reply. The thickness of ZnSe layer is only several
micro. Therefore the etching rate by diamond paste roughening or Inert
plasma should be as small as possible. Otherwise the whole layer will be
etched away. I will try the two way in the near future.

Some use wet etching on ZnO for texturing surface. Maybe same wet etching
can be used on ZnSe.

Weiquan