High performance metamorphic In/sub 0.32/Al/sub 0.68/As/In/sub 0.33/Ga/sub 0.67/As HEMTs on GaAs substrate with an inverse step InAlAs metamorphic buffer

Recently, InAlAs-InGaAs high electron mobility transistors lattice mismatched on GaAs substrates (metamorphic HEMTs) have been subject to a great deal of interest and development. Metamorphic structures using a graded buffer offer an arbitrary choice of lattice constant and indium composition. Here, we present the successful realization of a high performance metamorphic In/sub 0.32/Al/sub 0.68/As-In/sub 0.33/Ga/sub 0.67/As HEMT grown on GaAs. This structure presents several advantages over the pseudomorphic HEMT. The high ΔE/sub c/ of 0.7 eV leads to a high sheet carrier density and good confinement; in addition, unstrained materials have a higher electron velocity, and the high band gap of In/sub 0.32/Al/sub 0.68/As gives a better Schottky barrier height. Metamorphic In/sub 0.32/Al/sub 0.68/As-In/sub 0.33/Ga/sub 0.67/As HEMT layers were grown by solid source molecular beam epitaxy on two-inch (100) GaAs substrates. The results for the devices produced demonstrate the processability and feasibility of high performance In/sub 0.32/Al/sub 0.68/As-In/sub 0.33/Ga/sub 0.67/As-GaAs HEMTs using an inverse step metamorphic buffer with low cross hatch.