Suppression of electrochemical etching effects in GaAs PHEMTs

The electrochemical etching effect is investigated in the recess etching of GaAs Pseudomorphic High Electron Mobility Transistors (PHEMTs). It is demonstrated that the electrochemical etching due to the exposed ohmic metals seriously effects the etch rate of InGaAs/AlGaAs and furthermore the production uniformity and yield. The electrochemical etching is a function of the distance from the device to the exposed metal and can be eliminated by increasing this distance to 2 mm and higher in our experiment The experimental results also indicate that the electrochemical effect is dependent on the semiconductor substrate resistance. By simply increasing the the substrate which is realized using B/sup +/ isolation implantation, the electrochemical effect can be reduced, or even eliminated.