In0.29Al0.71As/In0.3Ga0.7As heterostructures grown on GaAs substrates with a step-graded metamorphic InxCa1-xAs buffer were characterized. Cross-sectional TEM micrographs revealed that an unstrained and dislocation-free In0.3Ga0.7As layer used as a buffer can be obtained. A 0.6-mu m-long gate HEMT based on this heterostructure demonstrated a g(m) of 230 mS/mm, an f(T) of 23 GHz, and an f(max) of 73 GHz. (C) 1996 John Wiley & Sons, Inc.
