Effects of Electrochemical Etching on InP HEMT Fabrication

Optimum device performance in terms of noise and gain of AlInAs/GaInAs/InP High Electron Mobility Transistors (HEMTs) requires minimizing the contact resistance R
_C
. In several HEMT fabrication steps in device manufacturing it is common to expose highly doped semiconductors layers to heated solvents for prolonged periods of time. It is shown here that even a small amount of water or water vapor present during photoresist removals, metal lift-offs or related processes can dramatically affect the final device performance by promoting electrochemical etching of the semiconductor layers adjacent to metal stacks. In this paper, the impact of metal lift-off on erosion of HEMT epitaxial layers and Ohmic contact resistance is studied with respect to different layer doping levels, compositions and metal stacks forming the Ohmic contacts.