SELECTIVE WET ETCHING OF A GAAS ALXGA1-XAS HETEROSTRUCTURE WITH CITRIC ACID-HYDROGEN PEROXIDE SOLUTIONS FOR PSEUDOMORPHIC GAAS/ALXGA1-XAS/INYGA1-Y HETEROJUNCTION FIELD-EFFECT TRANSISTOR FABRICATION/

The selective wet etching characteristics of GaAs/Al-x Ga1-xAs1-x syst ems in citric acid-hydrogen peroxide solution have been studied for x = 0.15, x = 0.2 and x = 0.3 respectively. A 4:1 ratio of citric acid ( 50% by weight)-H2O2 solution was found to be a better selective etchan t than the more commonly used NH4OH-H2O2 solutions. The selectivity ob tained was more than 110 for x = 0.3. The simple and reliable selectiv e wet etchant was applied to the gate recess etching in the fabricatio n of pseudomorphic GaAs/AlxGa1-xAs/InyGa1-yAs heterojunction held effe ct transistors.