| abstract |
A method of forming an integrated circuit employs a plurality of layers formed on a substrate including i) n-type modulation doped quantum well structure (MDQWS) structure with n-type charge sheet, ii) p-type MDQWS, iii) undoped spacer layer formed on the n-type charge sheet, iv) p-type layer(s) formed on the undoped spacer layer, v) p-type etch stop layer formed on the p-type layer(s) of iv), and vi) p-type layers (including p-type ohmic contact layer(s)) formed on the p-type etch stop layer. An etch operation removes the p-type layers of vi) for a gate region of an n-channel HFET with an etchant that automatically stops at the p-type etch stop layer. Another etch operation removes the p-type etch stop layer to form a mesa at the p-type layer(s) of iv) which defines an interface to the gate region of the n-channel HFET, and a gate electrode is formed on such mesa. |