EFFECT OF STRAINED INGAAS STEP BUNCHING ON MOBILITY AND DEVICE PERFORMANCE IN N-INGAP/INGAAS/GAAS PSEUDOMORPHIC HETEROSTRUCTURES GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

We studied the surface of thin strained InGaAs layers grown on GaAs and n-GaAs/n-InGaP/ InGaAs/ GaAs pseudomorphic high electron mobility transistor (HEMT) structures using atomic force microscopy (AFM). We observed large step bunching from layer-by-layer growth more readily in InGaAs than in GaAs, due to strain. AsH3 annealing of the InGaAs surface induced step bunching movement, and reduced the surface free energy and strain. We investigated the effect of the InGaAs growth conditions on the heterointerface roughness in HEMTs by selectively etching n-GaAs and n-InGaP. We found that etched InGaAs differs from as-grown InGaAs and that the electron mobility in HEMT's is insensitive to InGaAs step bunching due to both the high sheet carrier density and the large step periodicity. Increasing InGaAs growth rate causes micro-alloy clustering although growth proceeds layer-by-layer, which affects the n-GaAs cap growth mode and degrades the mobility. Tertiarybutylarsine dan suppress step bunching because of its low decomposition temperature. We also investigated the effect of substrate misorientation and found that both the mobility and the quantum well characteristics were primarily affected by step type. We fabricated HEMTs with 1 mu m long gate electrodes parallel and perpendicular to the step bunching. We found that the step bunching slightly influences the K-value around the threshold voltage in HEMTs.