A study of wet chemical gate recess etching of pseudomorphic In0.15GaAs/GaAs HEMTS

During non-selective wet chemical gate recess etching of pseudomorphic In 0.15 GaAs/GaAs HEMTs, the rate of change of saturated drain current with etch time decreased suddenly to one-tenth of the initial rate when etching began. This reduced rate lasted for around 45 s of etching before the rate increased again. A simple model, based on Poisson's equation with a constant etch rate in all the layers of the HEMT structure, has been developed to explain the effect. This shows that the variation in the rate of change of drain current with etch time is related to the thickness and doping concentration of the layers in the HEMT structure. As will be explained, this has important ramifications for HEMT layer design.